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Adv Urol. 2008; 2008: 720840. Published online 2008 November 9. doi: 10.1155/2008/720840. | PMCID: PMC2581790 |
Copyright © 2008 José Antonio López-Guerrero et al. Genetic Counseling in Renal Masses José Antonio López-Guerrero,1* Zaida García-Casado,1 Antonio Fernández-Serra,1 and José Rubio-Briones2 1Laboratory of Molecular Biology, Fundación Instituto Valenciano de Oncología, C/Prof. Beltrán Báguena 8, 46009 Valencia, Spain 2Service of Urology, Fundación Instituto Valenciano de Oncología, C/Prof. Beltrán Báguena 8, 46009 Valencia, Spain Received March 29, 2008; Accepted September 9, 2008. This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. All urologists have faced patients suffering a renal cancer asking for the occurrence of the disease in their offspring and very often the answer to this question has not been well founded from the scientific point of view, and only in few cases a familial segregation tree is performed. The grate shift seen in the detection of small renal masses and renal cancer in the last decades will prompt us to know the indications for familial studies, which and when are necessary, and probably to refer those patients with a suspected familial syndrome to specialized oncological centers where the appropriate molecular and familial studies could be done. Use of molecular genetic testing for early identification of at-risk family members improves diagnostic certainty and would reduce costly screening procedures in at-risk members who have not inherited disease-causing mutations. This review will focus on the molecular bases of familial syndromes associated with small renal masses and the indications of familial studies in at-risk family members. Renal cell carcinoma
(RCC) affects approximately 150 000 people worldwide each year, causing close to 78 000 deaths annually, and its incidence seems to be
rising [ 1]. This rising trend is partially due
to the growing use of new and improved noninvasive abdominal imaging
modalities, such as ultrasonography, CT, and MRI [ 2, 3]. In more recent years, 48–66% of RCCs have
been detected incidentally as small renal masses in asymptomatic patients,
whereas historically most cases were diagnosed following investigations for flank
pain or hematuria [ 4]. RCC is not a single entity, but rather
comprises the class of tumors of renal epithelial origin. Broad histological
and molecular studies have resulted in a consensus classification of different
RCC subtypes ( Table 1) [ 5]. | Table 1Classification of renal epithelial tumors. |
Most cases of RCC are
thought to be sporadic whereas there has been estimated that hereditary RCC
syndromes are estimated at 1–4% but have major
clinical and scientific implications [ 6, 7]. First, the identification of
predisposing gene offers the possibility of genetic testing: surveillance of
mutation carriers results in early diagnosis and treatment. Secondly, the
involvement of the same genes is demonstrated in a number of sporadic RCCs, providing
insight into the various mechanisms of renal tumorigenesis [ 8]. To date, 10 familial syndromes
associated with one or more of the various histological subtypes of RCC have
been described, all of them inherited with an autosomal dominant trait, that
means that carrier individuals of a mutant allele
have a 50% chance of passing the mutant gene to the offspring and therefore the
associated disorder ( Table 2) [ 9]. The diverse nature of these
predisposing genes implicates different mechanisms and biological pathways in
RCC tumorigenesis. Hence, identification of mutations responsible for these
syndromes in healthy carriers constitutes a challenge in the clinical
management of these individuals. | Table 2Hereditary renal cell carcinoma (RCC) syndromes and histological subtypes. |
There are no generally accepted screening guidelines for hereditary RCC
syndromes; however, some recommendations can be made. A hereditary
predisposition to renal cancer should be suspected whenever an individual who
is diagnosed with renal cancer has a close relative also diagnosed with the
disease, and/or when an individual presents with multifocal renal tumors or a
history of previous renal tumor. Family history should be obtained and a
pedigree created, paying specific attention to relatives with a known history
of cancer. Whenever possible (when a gene-causing disease is identifiable), a
germline genetic testing should be performed on the proband. In addition, and
as a general rule, molecular genetic testing of at-risk family members is
appropriate in order to identify the need for continued, lifelong, clinical
surveillance. Interpretation of the result is most accurate when a disease-causing
mutation has been identified in an affected family member. Those who have a disease-causing mutation require lifelong regular
surveillance. Meanwhile, family members who have not inherited the mutation and their offspring have risks similar to the general
population [ 10]. In this case, and generally
speaking within a genetic testing context, the presence or absence of a
mutation in a predisposing gene or the type of mutation determines the clinical
actuation in cases of hereditary syndromes of cancer. In this sense, and
following the American College of Medical Genetics (ACMG) recommendations, we
can describe the following situations [ 10]: Situation 1. When the mutation is
present:
- the pathogenic sequence alteration is reported
in the literature;
- sequence alteration is predicted to be
pathogenic but not reported in the literature;
- sequence variation of unknown clinical
significance;
- sequence alteration is predicted to be benign
but not reported in the literature;
- a benign sequence alteration is reported in the
literature.
Situation 2. Possibilities if a
sequence alteration is not detected:
- patient does not have a mutation in the tested
gene (e.g., a sequence alteration exists in another gene at another locus);
- patient has a sequence alteration that cannot be
detected by sequence analysis (e.g., a large deletion, a splice site deletion);
- patient has a sequence alteration in a region of
the gene (e.g., an intron or regulatory region) not covered by the laboratory's
test.
Herein we review the
four most frequent syndromes (von Hippel-Lindau, Hereditary papillary RCC,
Hereditary leiomyomatosis RCC, and Birt-Hogg-Dubé), the molecular biology of
the associated genes, and the clinical consequences of a genetic counseling. 2. VON HIPPEL-LINDAU (VHL) DISEASE 2.1. Clinical manifestation and molecular biology VHL (OMIM: 193300) is
the main cause of inherited RCC [ 11]. This syndrome includes central
nervous system (CNS) and retinal hemangioblastomas, clear cell RCC and renal
cysts, pheochromocytomas, neuroendocrine pancreatic tumors and pancreatic
cysts, and endolymphatic sac tumors [ 12]. VHL occurs at a prevalence of
about 1/36 000 and VHL-associated tumors with relatively high penetrance (80–90%) develop in the
second to fourth decades of life. RCC affects up to 75% of patients by the age
of 60 years. RCC is predominantly multiple and bilateral and occurs at a mean
age of 39 years [ 11, 12] ( Table 3). | Table 3Hereditary
patterns and risks of renal cell carcinoma (RCC) associated syndromes. |
Genetically, VHL is caused
by germline mutations in the VHL tumor suppressor gene located on 3p25-26 accompanied by inactivation of the
wild-type copy of the VHL gene in a
susceptible cell through loss of heterozygosity (LOH), promoter
hypermethylation, or somatic mutation [ 6]. VHL disease tumor
suppressor protein (pVHL) has been implicated in a
variety of functions including transcriptional regulation, posttranscriptional gene expression, protein folding, extracellular matrix
formation, and ubiquitinylation [ 13]. The role of pVHL
in the regulation of hypoxia-inducible genes through the
targeted ubiquitinylation and degradation of hypoxia-inducible factor-1 α (HIF1 α) has been
elucidated, leading to a model of how disruption of the VHL gene results in RCC and
the production of highly vascularized tumors. Under normoxic
conditions, HIF1 α is hydroxilated (−OH) on two
conserved praline residues by a member of the EGLN family of prolyl hydroxylase
enzymes. This hydroxylation provides a substrate-recognition site for the
pVHL-E3 ubiquitin ligase complex, which contains elongins C and B, cullin-2
(CUL2), and RBX1. Polyubiquitylation of HIF1 α by the VHL complex leads to its
proteasomal degradation by the 26S proteasome [ 6] (). However, under hypoxic
conditions, HIF1 α is not hydroxylated, pVHL does not
bind, and HIF1 α subunits accumulate. HIF1 α forms heterodimers with HIF1 β and activates transcription of a variety of hypoxia-inducible genes (i.e., VEGF, EPO, TGF α, PDGF β). Likewise, when pVHL is absent or mutated, HIF1 α subunits accumulate, resulting in
cell proliferation and the neovascularization of tumors characteristic of VHL
disease [ 13]. Mutations in the VHL gene either prevent its expression
(i.e., deletions, and frameshifts, nonsense mutations, splice site mutations) or lead to the
expression of an abnormal protein (i.e., missense mutations), and interesting
genotype-phenotype correlations are emerging for VHL disease that relate to the
development of RCC [ 14]. A group of VHL mutations termed type 1, comprising mostly deletions and
premature-termination mutations that cause total loss of pVHL function,
predispose to the entire spectrum of VHL-syndrome except pheocromocytomas [ 15]. By contrast, type 2 mutations,
which are mostly missense changes that reduce pVHL activity, predispose to the
entire VHL spectrum, including pheochromocytomas with or without RCC, called
type 2B and type 2A, respectively [ 6]. Several studies have revealed that
type 1 and type 2B mutations, which predispose to RCC, show complete loss of HIF1 α ubiquitylation and regulation,
whereas type 2A mutations result in an incomplete defect in HIF regulation [ 16]. However, type 2A mutations have
been shown to disrupt binding of pVHL to microtubules and abrogate the
associated microtubule-stabilizing function of pVHL, implicating defective
cytoskeleton organization in this VHL phenotype [ 17]. A third VHL-syndrome subclass
(type 2C)
predisposes almost exclusively to pheochromocytomas [ 9]. Type 2C mutations produce pVHL that
regulates HIF but is defective in fibronectin assembly, indicating a possible
link between fibronectin-matrix assembly and pheochromocytoma development [ 17]. Another class of VHL point mutations inactivates pVHL
function by disrupting proper protein folding mediated by chaperonin TriC/CCT [ 18]. More recently, two independent groups
reported a reduced risk for RCC in individuals with a complete deletion of the VHL gene. This group of individuals would define a new VHL phenotype characterized by a low risk for both RCC and
pheochromocytoma [ 19, 20]. 2.2. Molecular genetic testing The molecular genetic
testing of VHL is mainly performed by
sequence analysis of all three exons which detects point mutations and small deletions or insertions
and that represents the 72% of VHL mutations, and deletion analysis (by means of Southern Blot, MLPA, quantitative
PCR, etc.) for detecting partial or complete gene deletions, which account for approximately
28% of all VHL mutations [ 21, 22]. Over 300 different VHL germline mutations have been
identified [ 6, 11]. The mutations occur in all three exons, with only a handful of mutations found in four or more families
(i.e., delPhe76, Asn78Ser, Arg161X, Arg167Gln, Arg167Trp, Leu178Pro). Codon 167 is a hot spot mutation. A database of mutations in the VHL gene is maintained on the human gene mutation database website http://www.hgmd.cf.ac.uk/ac/index.php. Molecular genetic testing is indicated in all individuals
known to have or suspected of having VHL syndrome [ 23]. Since the detection rate for VHL gene mutations is nearly 100%, molecular testing
may also be used to evaluate individuals with a single VHL-associated tumor and
a negative family history of the disease. In addition, for individuals with
manifestations of VHL syndrome who do not meet strict diagnostic criteria and
who do not have a detectable VHL germline mutation, somatic mosaicism
for a de novo VHL disease-causing mutation should be considered. In some
instances, molecular genetic testing of the offspring of such
individuals reveals a VHL mutation [ 24]. The level of mutation detection obtained by molecular genetic testing of the VHL makes it possible
to effectively rule out VHL syndrome with a high degree of certainty in
individuals with isolated hemangioblastoma, retinal angioma,
or clear cell RCC, who have no detectable VHL disease-causing germline mutation; somatic mosaicism for a VHL gene mutation still needs to be considered in
such individuals. A younger individual, especially one with multiple lesions,
is more likely to have a germline VHL mutation than an older individual with a
single lesion [ 25]. Since pheochromocytoma
is part of the VHL syndrome spectrum and may occur as the exclusive
manifestation of VHL syndrome (type 2C),
individuals with a family history of these tumors, or those in whom
the disease is bilateral or multifocal, should be offered molecular genetic testing for VHL germline mutations [ 26]. Germline VHL mutations are rare in simplex cases of unilateral pheochromocytoma
(i.e., an affected individual with no family history of VHL syndrome), unless the
individual is younger than age 20 years. Exceptions are those individuals with
a family history that is more consistent with familial paragangliomas of the head and
neck, which are caused by mutations in various subunits of the gene encoding succinic dehydrogenase (SDH)
[ 27, 28], or those individuals who have
features of other heritable diseases associated with pheochromocytoma such as multiple endocrine neoplasia type 2A
or 2B or neurofibromatosis type 1 [ 25]. Use of molecular genetic testing for early identification of at-risk family members improves diagnostic certainty and
reduces the need for costly screening procedures in those at-risk family
members who have not inherited the disease-causing mutation [ 29]. In addition, the American Society
of Clinical Oncologists (ASCO) identifies VHL syndrome as a Group 1 disorder, that
is, a hereditary syndrome for which genetic testing is considered part of the
standard management for at-risk family members [ 30]. Early recognition of
manifestations of VHL syndrome may allow for timely intervention and improved
outcome; thus, clinical surveillance of asymptomatic at-risk individuals,
including children, for early manifestations of VHL syndrome is appropriate. 2.3. Genetic counseling Genetic
counseling is the process of providing individuals and families with
information on the nature, inheritance, and implications of genetic disorders
to help them make informed medical and personal decisions. As mentioned above, VHL
syndrome is inherited in an autosomal dominant manner, and we call proband (or
index case) to the affected individual through whom a family
with a genetic disorder is ascertained. It has been reported that about 80% of
individuals diagnosed with VHL syndrome have an affected parent whereas de novo mutations of the VHL gene are estimated to occur in about 20%
of probands. Recommendations for the evaluation
of parents of a proband with an apparent de novo mutation include molecular genetic testing if the VHL disease-causing mutation in the proband is known. If the disease-causing VHL mutation in the proband is not known, ophthalmologic screening and abdominal ultrasound
evaluation, at a minimum, should be offered to both parents [ 31]. In the case of the sibs
of a proband, the risk of VHL syndrome to sibs depends upon the genetic status
of the parents: if a parent of a proband is clinically affected or has a disease-causing VHL mutation, the sibs of
the proband are at 50% risk of inheriting the altered gene; and if neither parent has the disease-causing VHL mutation identified in the proband, the sibs have a small risk of VHL syndrome because of
the possibility of germline mosaicism in one parent (at present the incidence of mosaicism
is not known) [ 24]. Each offspring of an affected individual has a 50% risk of
inheriting the mutant VHL gene; but the degree of clinical severity is
not predictable (), whereas the risk to other family members depends
upon their biological relationship to the affected family member and can be determined
by pedigree analysis and/or molecular genetic testing. Molecular genetic
testing of at-risk family members is appropriate in order to determine the need
for continued clinical surveillance. Interpretation of molecular genetic test
results is most accurate when a disease-causing germline mutation has been
identified in an affected family member. Those who have the disease-causing
mutation require regular surveillance, whereas family members who have not
inherited the disease-causing mutation and their offspring need have no
future concern [ 31]. Because early detection
of at-risk individuals affects medical management, testing of asymptomatic
individuals during childhood is beneficial [ 30]. As ophthalmologic screening for
those at risk for VHL syndrome begins as early as possible, certainly before
age five years, molecular genetic testing may be considered in young children. Molecular
genetic testing may be performed earlier if the results would alter the medical
management of the child. The use of molecular
genetic testing for determining the genetic status of presumably at-risk
relatives when a family member with a clinical diagnosis of VHL syndrome is not
available for testing is less straightforward. Such test results need to be
interpreted with caution. A positive test result signals the presence of a VHL disease-causing
mutation in the at-risk family member and indicates that the same molecular genetic
testing method can be used to assess the genetic status of other at-risk family
members. However, a negative test for a VHL gene mutation under such circumstances suggests one of the
following possibilities:
- the at-risk family member has not inherited a VHL disease-causing
mutation;
- the familial VHL mutation may not be detectable by the assays
used; or
- the diagnosis of VHL syndrome in the affected family member is
questionable.
In this situation, the
presumably at-risk family member has a small, but finite, residual risk of
having inherited a disease-causing allele (i.e., VHL syndrome or other
hereditary disorder). In counseling such individuals, careful consideration
should be given to the strength of the clinical diagnosis of VHL syndrome in
the affected family member, the relationship of
the at-risk individual to the affected family member, the perceived risk
of an undetected VHL (or other) gene mutation, and the potential need for some
form of continued clinical surveillance [ 31]. It is recommended that
physicians ordering VHL molecular genetic testing and individuals
considering undergoing testing understand the risks, benefits, and limitations
of the testing prior to sending a sample to a laboratory. In fact, in some
countries the individuals must give and sign an informed consent before the
genetic analysis. When neither parent of a
proband with an autosomal dominant condition has the disease-causing mutation
or clinical evidence of the disorder, it is likely that the proband has a de novo mutation. However,
possible nonmedical explanations including alternate paternity or maternity
(i.e., with assisted reproduction) or undisclosed adoption could also be
carefully explored. 3. HEREDITARY PAPILLARY RCC 3.1. Clinical manifestation and molecular biology Hereditary papillary RCC
(HPRCC) (OMIM 605074) is characterized by the development of multifocal, bilateral
papillary type-1 RCCs (low-grade tumors with basophilic cells and a favorable
prognosis) occurring at a late age in ~20% of gene carriers and a male/female
ratio of 2:1 among affected members [ 6, 32] ( Table 3). The pattern of
inheritance is consistent with autosomal dominant transmission with reduced
penetrance. Metastasis is less frequent, and age-dependent penetrance in
mutation carriers seems to be reduced relative to penetrance in VHL syndrome [ 6]. HPRCC is mainly caused
by activating germline mutations in the tyrosine kinase domain of the MET proto-oncogene. MET is located in 7q31 and codifies a
tyrosine kinase receptor that is normally activated by hepatocyte growth factor
(HGF) [ 33] ( Table 2). The MET–HGF signalling
pathway is important for cell proliferation, epithelial–mesenchymal
transitions, branching morphogenesis, differentiation and regulation of cell
migration in many tissues. Most of the germline mutations occur within the MET
activation loop or in the ATP-binding pocket and cause ligand-independent MET
activation () [ 34]. Tumors from patients with
papillary RCC and germline mutations of MET commonly show trisomy of chromosome 7 when analyzed by cytogenetic studies and
comparative genomic hybridization (CGH) providing the second activating event
in the renal cells [ 9]. 3.2. Molecular genetic testing The molecular genetic
testing of MET is mainly performed by
sequence analysis of exons 16 to 19. All reported alterations consist in point
mutations. Ten known mutations are clustered in exons 16–19 of the tyrosine
kinase domain and all are missense mutations which change the amino acid
(V1110I, H1112R, H1112Y, M1149T, V1206L, V1238I, D1246N, Y1248C, Y1248D,
M1268T). Mutations at four codons (V1110, D1246, Y1248, M1268) are homologous
to sites of disease-associated activating mutations in other RTKs (RET, c-kit,
c-erbB). Two unrelated North American families have been identified with the
H1112R mutation and shared flanking genotyping data, suggesting a founder
effect. Other mutations with only weak transforming potential (Y1248C, L1213V)
confer anchorage-independent growth and an invasive phenotype in transfected
cells. Molecular genetic testing for a germline MET mutation is indicated in all individuals
known to have or suspected of having HPRCC. 3.3. Genetic counseling There are no specific
screening guidelines for families suspected of having HPRCC. Individuals in
these families are encouraged to talk with their doctor about screening options
for kidney cancer, including ultrasound, and CT scan. Some clinicians suggest
that individuals who have HPRCC, or a family history that suggests HPRCC,
should have yearly screening beginning at age 30. 4. HEREDITARY LEIOMYOMATOSIS RCC 4.1. Clinical manifestation and molecular biology Hereditary
leiomyomatosis renal cell cancer (HLRCC) (OMIM 605839) predisposes to multiple
cutaneous and uterine leiomyomas and solitary papillary type 2 RCCs [ 6, 35] ( Table 2). The majority of
individuals (76%) present with a single or multiple cutaneous leiomyoma. These
lesions appear as skin-colored to light brown papules or nodules distributed
over the trunk and extremities, and occasionally on the face. Forty percent of
individuals with HLRCC have mild cutaneous manifestations with five or fewer
lesions [ 36]. Histologically, proliferation of
interlacing bundles of smooth muscle fibers with centrally located long
blunt-edged nuclei is observed. Practically all females
with HLRCC develop uterine leiomyomas [ 36– 38]. However, whether all women with
HLRCC have a higher risk of developing uterine leiomyosarcomas is unclear. In
the original description of HLRCC, it was reported that 15% of women with
uterine leiomyomas also had uterine leiomyosarcoma [ 39]. Most renal tumors are
unilateral and solitary. Approximately 10%–16% of
individuals with HLRCC who present with multiple cutaneous leiomyomas had renal
tumors at the time that renal imaging was performed [ 37, 38]. Most tumors are classified as “type
2” papillary renal cancer, which display distinct papillary architecture and
characteristic histopathology (high-grade tumors with large eosinophilic cells,
an aggressive course, and a bad prognosis) [ 38] ( Table 3). The median age at
detection of renal tumors is 44 years, and, in contrast to other hereditary
renal cancer syndromes, renal cancers associated with HLRCC are aggressive [ 38]. The disease is caused by
germline mutations in the tumor suppressor gene FH located in 1q42-43 that encodes the
mitochondrial Krebs cycle enzyme fumarate hydratase (EC
4.2.1.2.) [ 35]. FH consists of ten exons
encompassing 22.15 kb of DNA and is highly conserved across species. The active form of the enzyme is a homotetramer and catalyzes the
conversion of fumarate to L-malate. In mammals, there are two fumarase isoforms
(mitochondrial and cytosolic) that are synthesized from the same mRNA. After
initial synthesis, the FH proteins are partially imported and
processed at the mitochondrial outer membrane [ 6]. Activity of FH enzyme
can be measured in cultured skin fibroblasts or lymphoblastoid cells to confirm
the diagnosis. Reduced activity (≤60%) of FH enzyme was found in all affected individuals with the diagnosis of
HLRCC [ 40, 41]. The overall risk for
renal tumor development is unclear and the mechanism of FH-mutation-driven tumorigenesis remains unknown so far [ 6]. It is plausible that intracellular
fumarate accumulation as a result of FH inactivation causes decreased
HIF degradation and overexpression of genes more downstream in the HIF pathway [ 42]. 4.2. Molecular genetic testing
FH is the only gene known to be associated with HLRCC. Between
80% and 100% of individuals with HLRCC have identifiable sequence variants in FH [ 36– 38]. The spectrum of mutations includes missense,
insertion/deletion, and nonsense mutations that are predicted to truncate the
protein, or substitute or delete highly conserved aminoacids, along with
several whole-gene deletion. About 40 different FH mutations have been identified and are distributed throughout the
entire gene without genotype-phenotype
correlation [ 40]. Several of the mutations occur in
many families, which could reflect a founder effect; notably, the Arg190His
mutation, which is the most frequent mutation (33%) in a North American family
study, and the Arg58X and Asn64Thr mutations in studies by the European-based
Multiple Leiomyoma Consortium [ 6]. Molecular genetic testing for a germline FH mutation is indicated in all individuals
known to have or suspected of having HLRCC, including individuals with the following:
- multiple cutaneous leiomyomas (with at least one
histologically-confirmed leiomyoma) without a family history of HLRCC;
- a single cutaneous leiomyoma with family history of HLRCC;
- one or more tubulo-papillary, collecting-duct, or papillary type 2 renal
tumors with or without a family history of HLRCC.
Measurement of FH enzyme activity can be useful in the diagnosis of HLRCC in
cases with atypical presentation and undetectable FH mutations [ 40, 41]. No correlation is
observed between FH mutations and the occurrence of cutaneous
lesions, uterine fibroids, or renal cancer of HLRCC [ 36]. To date, six women with a germline mutation in FH have been reported
with uterine leiomyosarcoma [ 43, 44]. It seems that FH mutation-positive families are in general not highly predisposed to uterine
cancer, but a few individuals and families seem to be at high risk. 4.3. Genetic counseling HLRCC is inherited in an
autosomal dominant manner. Some individuals diagnosed with HLRCC have an affected parent and some have HLRCC as the result of a de novo gene mutation. In this case, the proportion of cases caused by de novo mutations is unknown as subtle manifestation in parents has not
been evaluated and genetic testing data are insufficient. Recommendations for
evaluation of parents of a proband with a suspected de novo mutation include molecular genetic testing if the FH disease-causing mutation in the proband has been identified. However, it is important to note
that although some individuals diagnosed with HLRCC have an affected parent, the family history may appear to be negative because of failure to
recognize the disorder in family members, early death of the parent before the
onset of symptoms, or late onset of the disease in the affected parent. In the case of the
siblings of a proband, the risk depends upon the genetic status of the
proband's parents. If a parent of a proband is clinically affected or has a disease-causing mutation, each sibling of the proband is at a 50% risk of inheriting the mutation. If the disease-causing mutation cannot be detected
in the DNA of either parent, the risk to siblings is low, but greater
than that of the general population because the possibility of germline mosaicism exists [ 38]. The risk to other family
members depends upon the status of the proband's parents. If a parent is found
to be affected or to have a disease-causing
mutation, his or her family members are at risk. It is not possible to predict whether symptoms will occur, or if they do,
what the age of onset, severity, and type of symptoms, or rate of disease
progression will be in individuals who have a disease-causing mutation. When neither parent of a proband with an autosomal dominant condition has the disease-causing
mutation or clinical evidence of the disorder, it is likely that the proband has a de novo
mutation. However, possible nonmedical explanations including alternate paternity or undisclosed adoption could also be
explored. There is no consensus on
clinical surveillance for HLRCC individuals so far but the following provisional
recommendations have been accepted until a consensus conference is conducted [ 31]. Individuals with the
clinical diagnosis of HLRCC, individuals with heterozygous mutations in FH without clinical manifestations, and at-risk
family members who have not undergone molecular genetic testing should have the following regular
surveillance by physicians familiar with the clinical manifestations of HLRCC.
-
Skin. Full skin examination is recommended annually
to every two years to assess the extent of disease and to evaluate for changes
suggestive of leiomyosarcoma.
-
Uterus. Annual gynecologic consultation is recommended
to assess severity of uterine fibroids and to evaluate for changes suggestive
of leiomyosarcoma.
-
Kidneys. If both the initial (baseline) and the first
annual follow-up abdominal CT scan with contrast are normal, this evaluation
should be repeated every two years.
Any suspicious renal
lesion (indeterminate lesion, questionable or complex cysts) at a previous
examination should be followed with a CT scan with and without contrast. PET-CT
may be added to identify metabolically active lesions suggesting possible
malignant growth. It must be taken into consideration that ultrasound
examination alone is never sufficient. Renal tumors should be
evaluated by a urologic oncology surgeon familiar with the renal cancer of
HLRCC. 5. BIRT-HOGG-DUBÉ SYNDROME 5.1. Clinical manifestation and molecular biology Birt-Hogg-Dubé (BHD) syndrome (OMIM 135150) is a genodermatosis that
predisposes individuals to benign cutaneous lesions of the face and neck, spontaneous
recurrent pneumothorax and/or lung cysts, and renal tumors [ 6, 7]. Approximately 15–29% of
individuals with BHD syndrome have renal tumors [ 45, 46] ( Table 3). The renal tumors are
usually bilateral and multifocal. Tumor types include renal oncocytoma,
chromophobe RCC, oncocytic hybrid tumor, and a minority of clear cell RCC [ 47]. The most common tumors are a
hybrid of oncocytoma and chromophobe histologic cell types, so-called oncocytic
hybrid tumor (67%), chromophobe RCC (23%), and renal oncocytoma (3%). Only
renal oncocytoma is considered a benign tumor [ 48]. Other types of renal tumors
reported in lower frequency include clear cell RCC and papillary renal
carcinoma. Most renal tumors are slow-growing. Median age of diagnosis is 48
years with range from 31 to 71 years [ 46]. The disease is caused by
germline mutations in the BHD (FLCN) gene on chromosome 17p11.2 [ 49]. BHD encodes folliculin, a new protein with unknown function but it is highly expressed in a variety of tissues including skin
and skin appendages, type 1 pneumocytes, and distal nephrons of the kidney [ 50]. Recent studies suggest that
folliculin might be involved in energy and/or nutrient sensing through the AMPK
and mTOR signaling pathways [ 51].
BHD somatic
mutations are very rare in sporadic RCC but hypermethylations are encountered in ~30% of all RCC
histological types [ 52]. Germline mutations in BHD,
plus somatic mutations and loss of heterozygosity in tumor tissue, suggest that loss
of function of the folliculin protein is the basis of tumor formation in
BHD syndrome [ 53]. 5.2. Molecular genetic testing
BHD is the only gene known to be associated with BHD
syndrome. Various mutations have been identified in families
with BHD syndrome. All mutations predict protein truncation. The most common mutation is cytosine insertion or deletion, which occurs in a polycytosine
tract in exon 11, suggesting the presence of a
hypermutable hot spot [ 46, 47]. Fifty-three percent of families
with BHD syndrome have been found to have an insertion or deletion in the polycytosine tract in exon 11 (mutational hot spot) [ 46]. Sequence analysis of all coding exons (exon 4–14) increases the mutation detection in probands to 84% [ 46]. Molecular genetic testing is indicated in all individuals
known to have or suspected of having BHD syndrome including individuals with
the following.
- Five or more facial or
truncal papules with at least one histologically confirmed fibrofolliculoma [54] with or without family history of BHD.
- A family history of BHD syndrome with a single
fibrofolliculoma or a single renal tumor or history of spontaneous pneumothorax.
- Multiple and bilateral
chromophobe, oncocytic, and/or oncocytic hydrid renal tumors.
- A single oncocytic,
chromophobe, or oncocytic-hydrid tumor and a family history of renal cancer with any of the above
renal cell tumor types.
- A family history of autosomal dominant primary spontaneous pneumothorax
without a history of chronic obstructive
pulmonary disease.
Mutations in BHD were found in
families with dominantly inherited spontaneous pneumothorax. Pulmonary
involvement appears to be the only manifestation; penetrance is 100% [ 55, 56]. Acquired mutations in BHD have been identified
in sporadic clear cell renal cell carcinoma [ 52, 57] and colon cancer [ 58, 59] without other associated tumors
characteristic of the heritable disease. No correlation is observed between type of BHD mutation and pulmonary and cutaneous
manifestations. However, individuals who have a deletion in the polycytosine tract of exon 11 may have a lower risk of
developing renal cancers than individuals with other mutations [ 46]. 5.3. Genetic counseling BHD syndrome is
inherited in an autosomal dominant manner. Some individuals with BHD
syndrome have an affected parent and some have BHD syndrome
as a result of a de novo gene mutation. The proportion of cases caused by de
novo mutations is unknown as a sufficient number
of parents have not been evaluated for subtle manifestations, nor are there
sufficient data on clinically unaffected parents who have been evaluated by molecular genetic testing. Recommendations for the evaluation
of parents of a proband with a suspected de novo mutation include molecular genetic testing if the disease-causing mutation in
the BHD gene in the proband is identified. But, although some
individuals diagnosed with BHD syndrome have an affected parent, the family history may appear to be negative because
of failure to recognize the disorder in family members, early death of the
parent before the onset of symptoms, or late onset of the disease in the affected parent. The risk to the siblings
of the proband depends upon the genetic status of
the proband's parents. If a parent of a proband is clinically affected or has a disease-causing mutation,
the sibs of the proband are at a 50% risk of inheriting the
mutation. If neither parent has the disease-causing mutation identified in the proband, the risk to sibs is low, but
greater than that of the general population because the possibility of germline mosaicism exists. When neither parent of a proband with an autosomal dominant condition has the disease-causing
mutation or clinical evidence of the disorder, it is likely that the proband has a de novo
mutation. However, other possible nonmedical explanations
could also be explored. There is no consensus on
clinical surveillance; therefore, these recommendations are provisional until a
consensus conference is conducted. Individuals with known BHD
syndrome, individuals known to have disease-causing mutations in BHD without
clinical manifestation, and at-risk family members who have not undergone
genetic testing should have regular monitoring by physicians familiar with the
spectrum of BHD syndrome. In particular, surveillance for and monitoring of
renal tumors include the following:
- if normal at baseline, abdominal/pelvic CT scan with contrast every two
years;
- if any suspicious lesion (indeterminate lesion, questionable or complex
cysts) at previous examination, annual abdominal/pelvic CT scan with contrast
alternating every other year with MRI to reduce lifetime exposure to radiation;
- evaluation of renal tumors by a urologic surgeon;
- monitoring of tumors less than three centimeters in diameter by periodic
imaging; they may not require surgical intervention while this small.
The identification of
genes responsible for inherited RCC has resulted in a better understanding of
renal tumorigenesis including sporadic RCC and is paving the way for new
therapeutic approaches [ 6, 7]. For VHL, recent and ongoing
insights into the functions of the VHL gene, especially the HIF-ubiquitylation pathway,
provide an attractive molecular basis for the development of specific
inhibitors of HIF and/or its downstream targets [ 13]. Preliminary studies with the VEGF receptor
inhibitor SU5416 showed that at least a third of patients with advanced VHL
disease improved their clinical status giving promising expectations [ 60]. In same directions, new protein
kinase receptor inhibitors are emerging [ 9]. In HPRCC, MET inhibitors gave
encouraging results in in vitro
studies, but clinical trials have started very recently and although data on
the antitumor activity of the anti-MET compounds are not yet available, these
studies have shown that MET inhibition results in low-grade toxicity, in
agreement with the preclinical analyses performed in animal models [ 61, 62]. Recent studies suggest
that HIF overexpression is involved in HLRCC tumorigenesis [ 42, 63]. Therefore, future target therapies
for HLRCC-associated tumors may include, for example, anti-HIF therapies such
as R59949 that regulate prolyl hydroxylase activity, thus preventing HIF
accumulation. The study of families
with increased rates of cancer will continue to yield more insight into the
factors that increase cancer risk. Genetic predisposition in the form of
mutations and polymorphisms will increasingly be catalogued and DNA-level
genetic profiling of high-risk families and individuals will become
commonplace. The increase in availability of genetic testing and counseling for
high-risk families should prove both helpful and cost-effective, as genetically
unaffected family members reassured regarding their health status and removed
from lifelong follow-up screening programmes. Finally, we also should
keep in mind, although not deeply discussed in this review, the psychological and
ethical implications of the genetic counseling [ 64– 66], not only from the strictly clinical
point of view, but also regarding the management of personal genetic
information that could have an impact on the individual and their relatives from
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LINDAU (VHL) DISEASE
