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Legius Syndrome

Synonym: Neurofibromatosis Type 1-Like Syndrome

, MD, , MD, PhD, , MD, and , MD.

Author Information
, MD
University of Utah
Salt Lake City, Utah
, MD, PhD
University of Utah
Salt Lake City, Utah
, MD
University of Utah
Salt Lake City, Utah
, MD
University of Utah
Salt Lake City, Utah

Initial Posting: ; Last Revision: May 12, 2011.

Summary

Disease characteristics. Legius syndrome is characterized by multiple café au lait macules without neurofibromas or other tumor manifestations of neurofibromatosis type 1 (NF1). Additional clinical manifestations reported commonly include intertriginous freckling, lipomas, macrocephaly, and learning disabilities / ADHD / developmental delays. Current knowledge of the natural history of Legius syndrome is based on the clinical manifestations of fewer than 200 individuals with a molecularly confirmed diagnosis; better delineation of the clinical manifestations and natural history of Legius syndrome will likely occur as more affected individuals are identified.

Diagnosis/testing. The diagnosis of Legius syndrome is difficult to make on clinical grounds alone. Detection of a mutation in SPRED1, the only gene known to be associated with Legius syndrome, is necessary to confirm the diagnosis.

Management. Treatment of manifestations: Consideration of behavioral modification and/or pharmacologic therapy for those with ADHD; physical, speech, and occupational therapy for those with identified developmental delays; individualized education plans for those with learning disorders.

Surveillance: Routine screening for developmental delays, and behavioral and learning problems.

Genetic counseling. Legius syndrome is inherited in an autosomal dominant manner. Each child of an individual with Legius syndrome has a 50% chance of inheriting the mutation. Although uncommonly requested, prenatal diagnosis for pregnancies at increased risk is possible if the disease-causing mutation of an affected family member has been identified.

Diagnosis

Clinical Diagnosis

The cardinal feature of Legius syndrome is pigmentary dysplasia consisting of café au lait macules, with or without intertriginous freckling.

Additional clinical manifestations reported in multiple individuals are listed in Table 2.

The diagnosis of Legius syndrome is difficult to make on clinical grounds alone. Given the overlapping manifestations of other disorders with multiple café au lait macules – primarily neurofibromatosis type 1 (NF1) – detection of a SPRED1 mutation is necessary to confirm the diagnosis of Legius syndrome.

Molecular Genetic Testing

Gene. SPRED1 is the only gene known to be associated with Legius syndrome.

Clinical testing

Table 1. Summary of Molecular Genetic Testing Used in Legius Syndrome

Gene SymbolTest MethodMutations DetectedMutation Detection Frequency by Test Method 1
SPRED1Sequence analysisSequence variants 2Unknown 3
Deletion / duplication analysis 4Exonic / whole-gene deletionsUnknown 5

1. The ability of the test method used to detect a mutation that is present in the indicated gene

2. Examples of mutations detected by sequence analysis may include small intragenic deletions/insertions and missense, nonsense, and splice site mutations.

3. Of individuals evaluated for NF1 without an identifiable NF1 mutation, 3%-25% had an identifiable SPRED1 mutation [Brems et al 2007, Messiaen et al 2009, Pasmant et al 2009, Spurlock et al 2009].

4. Testing that identifies deletions/duplications not readily detectable by sequence analysis of genomic DNA; a variety of methods including quantitative PCR, long-range PCR, multiplex ligation-dependent probe amplification (MLPA), or targeted array GH (gene/segment-specific) may be used. A full array GH analysis that detects deletions/duplications across the genome may also include this gene/segment.

5. No exonic or whole-gene deletions or duplications involving SPRED1 as causative of Legius syndrome have been reported per se; however, Messiaen et al [2009] referenced three different multiexon deletions as unpublished data and Spencer et al [2011] report that deletions comprise approximately 10% of SPRED1 mutations.

Interpretation of test results. For issues to consider in interpretation of sequence analysis results, click here.

Testing Strategy

To confirm/establish the diagnosis in a proband

1.

Perform physical examination and take medical history to exclude other conditions associated with multiple café au lait macules. If an individual lacks the non-pigmentary clinical diagnostic manifestations of NF1 (e.g., Lisch nodules, neurofibromas, optic glioma, sphenoid wing dysplasia, long bone dysplasia), Legius syndrome must be considered in the age and family history of the affected individual.

2.

Obtain family history to identify other family members who may have findings consistent with Legius syndrome. Physical examination for features of Legius syndrome or NF1 should be performed in both parents of the affected individual. For example, if the parent of a child with multiple café au lait macules has multiple café au lait macules but no other features of NF1, Legius syndrome is more likely, particularly if mosaicism for NF1 in the parent is excluded.

3.

When clinical information and family history cannot distinguish between NF1 and Legius syndrome, consider molecular genetic testing (see following).

The assessment of pros and cons of molecular testing requires that the circumstances unique to each individual be considered, including (but not limited to): clinical findings and family history, age of the individual, differences in recommended clinical management when the diagnosis of NF1 or Legius syndrome is established with certainty versus when the diagnosis of neither can be established with certainty, psychological burden of a diagnosis or lack thereof, and costs of testing and surveillance. For recommended approaches, see Stevenson & Viskochil [2009].

Pasmant et al [2009] recommend molecular genetic testing for SPRED1 before molecular genetic testing for NF1 in post-pubertal individuals with a family history of café au lait spots and/or freckling without neurofibromas or Lisch nodules. This recommendation is based on the small size of SPRED1 and the expected high mutation detection rate in those with Legius syndrome. For those in whom no SPRED1 mutation is identified, consider either performing NF1 molecular genetic testing or following the recommendations for routine clinical surveillance for NF1.

In cases of diagnostic uncertainty Messiaen et al [2009] recommend analysis of NF1 first and, if no NF1 mutation is identified, consideration of SPRED1 testing. This recommendation is based on:

  • The increased likelihood of detecting an NF1 mutation as compared to a SPRED1 mutation in those with isolated pigmentary findings and an uninformative family history.
  • A mutation detection rate of 43.4% in NF1 versus 1.3% in SPRED1 in simplex cases (i.e., a single individual in a family) with the following:
    • >5 café au lait macules
    • ± freckling
    • No other NF1 diagnostic criteria
  • A mutation detection rate of 73.4% in NF1 versus 19% in SPRED1 in individuals with
    • >5 café au lait macules
    • ± freckling
    • No other NF1 diagnostic criteria, and
    • A parent who has the following:
      • Multiple café au lait macules
      • ± freckling
      • No other manifestations of NF1

In one NF1 clinic, Muram-Zborovski et al [2010] found age to be an important factor when considering SPRED1 molecular genetic testing. Of the 61 individuals age ten years or older who fulfilled NF1 diagnostic criteria, four did not have Lisch nodules, neurofibromas, optic gliomas, sphenoid wing dysplasia, or long bone dysplasia. Of those four, two had a SPRED1 mutation.

Denayer et al [2011] concluded that there is a greater likelihood of finding a SPRED1 mutation in familial cases of multiple café au lait macules with or without freckling than in simplex cases with the same findings.

Given that exonic and whole-gene deletions may be as high as 10% [Messiaen et al 2009, Spencer et al 2011], one should consider deletion/duplication testing when no mutation is identified by sequence analysis.

Prenatal diagnosis and preimplantation genetic diagnosis (PGD) for at-risk pregnancies require prior identification of the disease-causing mutation in the family.

Clinical Description

Natural History

The natural history of Legius syndrome is based on the clinical manifestations of a few series of individuals with SPRED1 mutations and their extended families (summarized in the bulleted list that follows). Additional less common manifestations are listed in Table 2. Better delineation of the clinical manifestations and natural history of Legius syndrome will likely occur as more affected individuals are identified and followed prospectively.

Of note, the phenotype of Legius syndrome is based on the following reports of a relatively few (<200) individuals, in which the primary focus was on individuals with the overlapping pigmentary manifestations of neurofibromatosis type 1 (NF1).

  • Brems et al [2007]. Brems et al identified SPRED1 mutations in 37 individuals from five families with Legius syndrome and seven of 86 unrelated individuals with features of NF1 who did not have an identifiable NF1 mutation. All but one of the 44 individuals had café au lait macules with or without freckling. (The exception was a 60-year-old male).
  • Pasmant et al [2009]. SPRED1 mutations were identified in two of 49 index cases from an NF1 clinical research database in whom no NF1 mutation had been identified and in three of 12 index cases from a medical genetics clinic with findings that fulfilled the NIH NF1 diagnostic criteria but did not have neurofibromas, Lisch nodules, or an NF1 mutation. SPRED1 sequencing was performed in selected family members of these five probands. SPRED1 mutations were identified in a total of 18 individuals, including probands. All 18 individuals had multiple café au lait macules. Based solely on pigmentary findings, six of these 18 individuals fulfilled the NIH NF1 clinical diagnostic criteria (making assumptions for age-related size of café au lait macules and pubertal status).
  • Spurlock et al [2009]. SPRED1 mutations were identified in six of 85 index cases in whom no NF1 mutation had been identified. The 85 individuals lacked cutaneous neurofibromas, but no other clinical information was reported. A total of 6/85 individuals had SPRED1 mutations. Four of the six had a family history of café au lait macules, and five fulfilled the NIH NF1 clinical diagnostic criteria. No significant learning problems or developmental delays were reported in the probands. Family members of the six probands were recruited, and clinical details of a total of 12 affected individuals (including probands) were described.
  • Messiaen et al [2009]. The authors described individuals with SPRED1 mutations from two cohorts: 40 individuals as part of a clinical study (cohort 1) and 33 probands referred for NF1 molecular genetic testing in whom no NF1 mutation was identified (cohort 2). Of the 22 probands in cohort 1, six had a de novo mutation. After family members were evaluated, a total of 40 individuals with pathogenic SPRED1 mutations were included in cohort 1, and 20/40 fulfilled the NIH clinical diagnostic criteria for NF1. Only one individual (a 2-year old child) had no café au lait macules.

    In cohort 2 of 1318 individuals, 33 loss-of-function SPRED1 mutations were identified. Of 1087 individuals fulfilling NF1 NIH diagnostic criteria, 21 (1.9%) had a SPRED1 mutation, while 823 (76%) had an NF1 mutation. No individuals with Lisch nodules, neurofibromas, typical osseous lesions, or optic gliomas were reported among those with SPRED1 mutations. The highest probable predictive value for SPRED1 mutations in this cohort was observed in familial cases with more than five café au lait macules with or without freckling and absence of other features included in the NF1 diagnostic criteria. The authors state that the 27 probands in cohort 1 were most likely also part of cohort 2.
  • Muram-Zborovski et al [2010]. In 151 individuals who fulfilled the clinical diagnostic criteria for NF1 ascertained from an NF1 clinic, two had SPRED1 mutations. Both patients fulfilled NIH NF1 diagnostic criteria based on pigmentary findings, with more than five café au lait macules and intertriginous freckling; however, neither had Lisch nodules, neurofibromas, or any other tumor manifestation.
  • Denayer et al [2011]. Six of 35 probands with an NF1-like syndrome identified had a SPRED1 pathogenic mutation. Through various collaborations the authors added eight additional probands for a total of 14 families in their study; in these 14 families a total of 30 individuals with a SPRED1 mutation were identified. Two individuals had T2 hyperintense lesions on brain imaging; thus, the presence of such lesions cannot be used to differentiate between Legius syndrome and NF1. Of note, many individuals in these families had abnormalities of psychomotor development.

Table 2. Additional Findings Reported in Multiple Individuals in Studies of Legius Syndrome

Finding Study
Brems et al [2007] (n=44)Pasmant et al [2009] (n=18)Spurlock et al [2009] (n=12)Messiaen et al [2009] (n=40) 1Muram-Zborovski et al [2010] (n=2)Denayer et al [2011] (n=30)
Macrocephaly131111
Short stature (<5th centile)3108
Noonan-syndrome-like facies5112
Pectus anomalies337
Depigmented macules31
Vascular lesions112
Lipomas14222
Learning disabilities / ADHD / developmental delays 859216
Headaches42
Hearing loss21
Seizures21
Polydactyly12
Scoliosis4

ADHD = Attention deficit hyperactivity disorder

1. Clinical cohort (cohort 1). Data from Anonymous cohort not included due to potential overlap.

2. Includes angiolipoma

Almost invariably, individuals with Legius syndrome present with café au lait macules. In some instances, freckling of the axillary/groin region is present. Only two individuals (a 60-year-old male and a 2-year-old child), each with a presumed pathologic SPRED1 mutation, have been reported with no café au lait macules or freckling [Brems et al 2007, Messiaen et al 2009]. It is possible that the lack of pigmentary manifestations in the two-year-old is a result of the child’s young age. The number of café au lait macules increases with age in childhood, similar to what is observed in NF1 [Author, personal observation].

Absolute or relative macrocephaly has been seen in children and adults with Legius syndrome. However, the frequency of macrocephaly varied in different reports: head circumference was at or above the 97th centile in approximately 40% of individuals in one cohort [Brems et al 2007] but above the 95th centile in only 1/18 individuals in another cohort [Pasmant et al 2009].

Absolute short stature has not been frequently noted in most series (although Denayer et al [2011] reported it in 31%). Brems et al [2007] reported that in 52% of individuals, height was greater than the 50th centile. Growth charts for Legius syndrome have not been published.

Neurobehavioral and developmental problems are reported in individuals with Legius syndrome, but in many instances detailed descriptions are lacking. Messiaen et al [2009] reported three individuals who had hyperactivity and two who had attention deficits. Of the six individuals with developmental abnormalities described by Messiaen et al [2009], all had speech and/or language delays as the primary or only delay. In the 12 individuals with Legius syndrome described by Spurlock et al [2009], no learning or developmental problems were noted in the probands. Denayer et al [2011] reported five children with motor delay and five with speech delay, three individuals with ADHD, and 14 of 25 individuals with learning difficulties.

A small number of vascular anomalies have been reported, but the descriptions are incomplete and different in each instance. The vascular abnormalities include “tuberous hemangioma,” “inguinal hemangioma,” “large right temporal venous anomaly in brain,” and “vascular anomaly left lower leg.” Additional data are needed to determine if these reported vascular anomalies are tumors or malformations.

Examples of other findings reported in isolated or only a few individuals include fifth finger clinodactyly, Chiari I malformation, hypotonia, cataract, nephrolithiasis, urethral meatal stenosis, pulmonic stenosis and mitral valve prolapse, paroxysmal atrial tachycardia, tubular colonic adenoma, progressive dystonia, desmoids tumor, vestibular schwanomma, tenosynovial giant cell tumor, dermoid tumor of the ovary, non-small cell lung cancer, Wilms tumor, and monoblastic acute leukemia. Observations of clinical findings in single individual when only a small total number of affected individuals have been reported (<200) should be taken with caution because chance occurrence cannot be distinguished from specific disease associations.

Compared to NF1. Legius syndrome in general lacks the tumor manifestations typically observed in NF1 (i.e., Lisch nodules, neurofibromas, and central nervous system tumors). One report suggested that individuals with Legius syndrome are at an increased risk for leukemia [Pasmant et al 2009]; however, this is based on the observation of acute myeloblastic leukemia in only one individual, and no second hit mutation was found in SPRED1 in the leukemic cells. Further studies are needed to assess the potential risk of cancers in Legius syndrome, particularly given that SPRED1 is part of the Ras-MAPK signal transduction pathway, which is involved in several neoplasms.

Genotype-Phenotype Correlations

A variety of pathologic allelic variants (e.g., missense, nonsense, frameshift, splice-site) throughout SPRED1 have been reported. To date no genotype-phenotype correlations have been documented.

Penetrance

The vast majority of individuals with SPRED1 mutations have café au lait macules and/or freckling. Only two individuals (a 60-year-old male and a 2-year-old child), each with a presumed pathologic SPRED1 mutation, were reported not to have café au lait macules or freckling [Brems et al 2007, Messiaen et al 2009].

Anticipation

No evidence for anticipation exists.

Nomenclature

Individuals with SPRED1 mutations were initially described as having “neurofibromatosis type 1-like syndrome” (NFLS) – primarily because of the observation that the finding in many fulfilled the NIH NF1 clinical diagnostic criteria [Brems et al 2007]. Although NF1 and SPRED1 interact within the same signal transduction pathway, the majority of individuals with SPRED1 mutations share the pigmentary manifestations but lack the tumor findings associated with NF1. To clearly delineate this point in counseling sessions and to avoid confusion between NF1 and NF1-like syndrome, experts at the 13th European Neurofibromatosis Meeting suggested that the disorder be named “Legius syndrome” after Eric Legius, the senior author of the paper that first described the phenotype of SPRED1 mutations in humans [Brems et al 2007].

Prevalence

The prevalence of Legius syndrome is not known, but in two studies approximately 2% of individuals fulfilling diagnostic criteria for NF1 have SPRED1 mutations [Messiaen et al 2009, Muram-Zborovski et al 2010]. The incidence of NF1 is reported to be 1:3000 [Friedman & Birch 1997].

Differential Diagnosis

Of primary importance in the clinical delineation of Legius syndrome is establishing the absence of other manifestations associated with the large number of other syndromes with multiple café au lait macules. Although the diagnosis of Legius syndrome is difficult to make clinically with certainty without identification of a disease-causing SPRED1 mutation, the lack of additional clinical features can help to differentiate Legius syndrome from other conditions.

Neurofibromatosis 1 (NF1) is most frequently confused with Legius syndrome as some individuals with Legius syndrome fulfill the clinical diagnostic criteria for NF1 [NIH 1988, Gutmann et al 1997]. Approximately 3%-25% of individuals being evaluated for NF1 without an identifiable NF1 mutation in different settings have a SPRED1 mutation [Brems et al 2007, Messiaen et al 2009, Pasmant et al 2009, Spurlock et al 2009]. The vast majority of individuals with NF1 eventually develop Lisch nodules and neurofibromas, but these manifestations are age-related, making the clinical distinction of NF1 from Legius syndrome very difficult in young children. The non-pigmentary manifestations outlined in the NIH NF1 diagnostic criteria, such as Lisch nodules, neurofibromas, optic gliomas, sphenoid wing dysplasia or long bone dysplasia, have not been observed in Legius syndrome, and the presence of one of these manifestations differentiates NF1 from Legius syndrome. Caution is needed when trying to establish a diagnosis of NF1 based purely on pigmentary findings [Stevenson & Viskochil 2009].

The phenotypes associated with specific NF1 mutations are similar to Legius syndrome in many cases. A described genotype-phenotype correlation with the NF1 three-base-pair deletion removing a methionine (c.2970_2972delAAT in exon 17 using NF Consortium nomenclature or exon 22 using NCBI nomenclature), results in an attenuated NF1 phenotype with relative lack of neurofibromas [Stevenson et al 2006, Upadhyaya et al 2007]. An NF1 missense mutation (p.Leu1390Phe) was observed in a single multigenerational family that lacked neurofibromas and had features of Noonan syndrome with variable presence of Lisch nodules; however, the contribution of other modifiers cannot be excluded [Nyström et al 2009a].

Noonan syndrome. While individuals with Noonan syndrome occasionally have café au lait macules, they do not typically have large numbers of café au lait macules. Some individuals with SPRED1 mutations have been reported to have facial features consistent with Noonan syndrome, and at least one individual with Legius syndrome was previously diagnosed as having Noonan syndrome [Brems et al 2007]. Congenital heart disease is common in Noonan syndrome but has not been a consistent finding in Legius syndrome.

Autosomal dominant café au lait spots. Several families with multiple café au lait macules inherited in an autosomal dominant pattern have been described [Brunner et al 1993, Charrow et al 1993, Arnsmeier et al 1994, Abeliovich et al 1995, Nyström et al 2009b]. It is possible that some of these families harbor a SPRED1 mutation, although this phenotype in at least one family did not segregate with markers within the SPRED1 locus [Nyström et al 2009b].

Other conditions associated with multiple café au lait macules include LEOPARD syndrome, McCune-Albright syndrome, homozygous mismatch repair cancer syndrome (see Hereditary Non-Polyposis Colon Cancer), Bloom syndrome, Fanconi anemia, Russell-Silver syndrome, Bannayan-Riley-Ruvalcaba syndrome (see PTEN Hamartoma Tumor Syndrome), Costello syndrome, cardiofaciocutaneous syndrome, and tuberous sclerosis complex.

Management

Evaluations Following Initial Diagnosis

To establish the extent of disease and needs of an individual with a confirmed molecular diagnosis of Legius syndrome, the following evaluations are recommended:

  • Age-appropriate developmental assessment
  • Neuropsychiatric evaluation on entry into school system or sooner based on clinical findings
  • Detailed dermatologic evaluation for supportive findings

Treatment of Manifestations

The following are appropriate:

  • Consideration of behavioral modification or pharmacologic adjuvant therapy for individuals with ADHD.
  • Adjuvant therapies such as physical, speech, and occupational therapy for individuals with identified developmental delays.
  • Individualized education plans for learning disorders.

Surveillance

Consider periodic evaluation by a clinical geneticist to discuss manifestations associated with disorders of the Ras/MAPK pathway that may eventually be associated with Legius syndrome

Routine screening for developmental delays and behavioral and learning problems is appropriate.

Although vascular abnormalities have been reported in a few individuals with Legius syndrome, hypertension has not been reported. However, given the prevalence of vascular abnormalities and hypertension in NF1, it would seem appropriate to have regular blood pressure monitoring at each physician visit.

Evaluation of Relatives at Risk

See Genetic Counseling for issues related to testing of at-risk relatives for genetic counseling purposes.

Therapies Under Investigation

Search ClinicalTrials.gov for access to information on clinical studies for a wide range of diseases and conditions. Note: There may not be clinical trials for this disorder.

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. The following section deals with genetic risk assessment and the use of family history and genetic testing to clarify genetic status for family members. This section is not meant to address all personal, cultural, or ethical issues that individuals may face or to substitute for consultation with a genetics professional. —ED.

Mode of Inheritance

Legius syndrome is inherited in an autosomal dominant manner.

Risk to Family Members

Parents of a proband

  • Many individuals diagnosed with Legius syndrome have an affected parent.
  • A proband with Legius syndrome may have the disorder as the result of a new gene mutation. Because the majority of simplex cases (i.e., a single occurrence in a family) have not been evaluated sufficiently to determine if the mutation was de novo, the proportion of Legius syndrome caused by de novo mutations is not well elucidated. However, one report states that 6/23 probands with SPRED1 mutations in a clinical cohort had a de novo mutation [Messiaen et al 2009].
  • If the disease-causing mutation found in the proband cannot be detected in leukocyte DNA of either parent, two possible explanations are germline mosaicism in a parent or a de novo mutation in the proband. Although no instances of germline mosaicism have been reported, it remains a possibility.
  • Recommendations for the evaluation of parents of a proband with an apparent de novo mutation include physical examination by a clinical geneticist and SPRED1 molecular genetic testing. Evaluation of parents may determine that one is affected but has escaped previous diagnosis because of inability by health care professionals to recognize the syndrome and/or a milder phenotypic presentation. Therefore, an apparently negative family history cannot be confirmed until appropriate evaluations have been performed on both parents.

Note: (1) Although many individuals diagnosed with Legius 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. (2) If the parent is the individual in whom the mutation first occurred s/he may have somatic mosaicism for the mutation and may be mildly/minimally affected, although this has not been reported to date for Legius syndrome.

Sibs of a proband

  • The risk to the sibs of the proband depends on the genetic status of the proband’s parents.
  • If a parent of the proband is affected, the risk to the sibs is 50%.
  • When the parents are clinically unaffected, the risk to the sibs of a proband appears to be low.
  • The sibs of a proband with clinically unaffected parents are still at increased risk for Legius syndrome because of the possibility of reduced penetrance in a parent.
  • If the disease-causing mutation found in the proband cannot be detected in the leukocyte DNA of either parent, the risk to sibs is low, but greater than that of the general population because of the possibility of germline mosaicism.

Offspring of a proband. Each child of an individual with Legius syndrome has a 50% chance of inheriting the mutation.

Other family members. The risk to other family members depends on the status of the proband's parents. If a parent is affected, his or her family members may be at risk.

Related Genetic Counseling Issues

Considerations in families with an apparent de novo 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 non-medical explanations including alternate paternity or maternity (e.g., with assisted reproduction) or undisclosed adoption could also be explored.

Family planning

  • The optimal time for determination of genetic risk and discussion of the availability of prenatal testing is before pregnancy.
  • It is appropriate to offer genetic counseling (including discussion of potential risks to offspring and reproductive options) to young adults who are affected or at risk.

DNA banking is the storage of DNA (typically extracted from white blood cells) for possible future use. Because it is likely that testing methodology and our understanding of genes, mutations, and diseases will improve in the future, consideration should be given to banking DNA of affected individuals.

Prenatal Testing

Prenatal diagnosis for pregnancies at increased risk is possible by analysis of DNA extracted from fetal cells obtained by amniocentesis usually performed at about 15 to 18 weeks’ gestation or chorionic villus sampling (CVS) at approximately ten to 12 weeks’ gestation. The disease-causing mutation of an affected family member must be identified in the family before prenatal testing can be performed.

Note: Gestational age is expressed as menstrual weeks calculated either from the first day of the last normal menstrual period or by ultrasound measurements.

Requests for prenatal testing for conditions such as Legius syndrome are not common. Differences in perspective may exist among medical professionals and within families regarding the use of prenatal testing, particularly if the testing is being considered for the purpose of pregnancy termination rather than early diagnosis. Although decisions about prenatal testing are the choice of the parents, discussion of these issues is appropriate.

Preimplantation genetic diagnosis (PGD) may be an option for some families in which the disease-causing mutation has been identified.

Resources

GeneReviews staff has selected the following disease-specific and/or umbrella support organizations and/or registries for the benefit of individuals with this disorder and their families. GeneReviews is not responsible for the information provided by other organizations. For information on selection criteria, click here.

  • RASopathiesNet
    244 Taos Road
    Atlandena CA 91001
    Phone: 626-676-7694
    Email: lisa@rasopathies.org

Molecular Genetics

Information in the Molecular Genetics and OMIM tables may differ from that elsewhere in the GeneReview: tables may contain more recent information. —ED.

Table A. Legius Syndrome: Genes and Databases

Data are compiled from the following standard references: gene symbol from HGNC; chromosomal locus, locus name, critical region, complementation group from OMIM; protein name from UniProt. For a description of databases (Locus Specific, HGMD) to which links are provided, click here.

Table B. OMIM Entries for Legius Syndrome (View All in OMIM)

609291SPROUTY-RELATED EVH1 DOMAIN-CONTAINING PROTEIN 1; SPRED1
611431LEGIUS SYNDROME

Molecular Genetic Pathogenesis

SPRED1 encodes for a protein that negatively regulates MAPK signaling. Loss-of-function mutations in SPRED1 create mutant Spred1 proteins incapable of inhibiting Raf1 kinase activation. This results in uninhibited downstream Raf-MEK-ERK signaling [Brems et al 2007]. This uninhibited signaling and ultimately increased Ras signal propagation is similar to that observed in NF1 and likely results in the clinical overlap of these two syndromes.

For example, neurobehavioral problems are reported in individuals with Legius syndrome and NF1; this finding in Legius syndrome is biologically consistent with data in the mouse model showing that Spred1 protein is required for synaptic plasticity [Denayer et al 2008]. In addition, vascular anomalies are seen in other syndromes of the Ras-MAPK pathway (i.e., capillary malformation-arteriovenous malformation syndrome with RASA1 mutations), providing potential biologic support for an association with Legius syndrome.

Normal allelic variants. Muram-Zborovski et al [2010] identified a common SPRED1 haplotype matching GenBank reference sequence NG_008980 in 17.9% of their NF1 cohort and 12.5% of an unselected normal population. This haplotype differs from the more common reference sequence NC_000015 by four single nucleotide allelic variants (SNPs). Two of these normal variants are exonic, one in exon 3 and one in exon 7; the other two SNPs are within intron 5. See Table 3.

Table 3. Selected SPRED1 Normal Allelic Variants

DNA Nucleotide ChangeProtein Amino Acid ChangeReference Sequences
c.291A>Gp.Lys97LysNM_152594​.2
NP_689807​.1
c.1044C>Tp.Val348Val
c.424-8A>CNA
c.424-98C>TNA

Note on variant classification: Variants listed in the table have been provided by the author(s). GeneReviews staff have not independently verified the classification of variants.

Note on nomenclature: GeneReviews follows the standard naming conventions of the Human Genome Variation Society (www​.hgvs.org). See Quick Reference for an explanation of nomenclature.

NA = not applicable

Pathologic allelic variants. Pathologic variants have been identified throughout SPRED1, without a discernible mutation hotspot. The pathologic variants identified to date are primarily nonsense mutations, although frameshift and splice site mutations have also been described. A few missense mutations have also been identified within families; however, only a portion of these have been confirmed as pathologic using functional studies [Messiaen et al 2009].

Normal gene product. Spred1 protein is a 444-amino acid sprouty-related protein. It comprises an N-terminal EVH-1 domain, a central KIT binding domain, and a C-terminal SPRY domain. Spred1 belongs to a family of proteins that are negative regulators of the Ras/ERK pathway. Spred1 negatively regulates the Ras/ERK pathway by inhibiting Raf1 kinase activation [Tidyman & Rauen 2009].

Abnormal gene product. Mutations that result in Spred1 loss of function prevent its ability to inhibit Raf1 kinase activation, leading to increased downstream ERK signaling. Mutations have been identified within the N-terminal EVH-1 domain, the KIT binding domain, and the C-terminal SPRY domain.

References

Medical Genetic Searches: A specialized PubMed search designed for clinicians that is located on the PubMed Clinical Queries page Image PubMed.jpg

Literature Cited

  1. Abeliovich D, Gelman-Kohan Z, Silverstein S, Lerer I, Chemke J, Merin S, Zlotogora J. Familial cafe au lait spots: a variant of neurofibromatosis type 1. J Med Genet. 1995;32:985–6. [PMC free article: PMC1051784] [PubMed: 8825931]
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Chapter Notes

Acknowledgments

John Carey, MD; Ludwine Messiaen, PhD

Revision History

  • 12 May 2011 (cd) Revision: Testing Strategy; Table 2
  • 14 October 2010 (me) Review posted live
  • 29 April 2010 (ds) Original submission
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