Clinical Description
The primary clinical features of Fanconi anemia (FA) include physical abnormalities, progressive bone marrow failure manifest as pancytopenia, and cancer susceptibility; however, some individuals with FA have neither physical abnormalities nor bone marrow failure.
Table 2.
Fanconi Anemia: Frequency of Select Features
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| Feature | % of Persons w/Feature |
|---|
| Growth deficiency | 65% |
| Abnormal skin pigmentation | 40% |
| Skeletal malformations of upper limbs | 40% |
| Skeletal malformations of lower limbs | 5% |
| Microcephaly | 20%-25% |
| Kidney / urinary tract anomalies | 20%-25% |
| Anomalies of internal & external genitalia | Males: 25% Females: 2% |
| Endocrine disorders | 50%-75% |
| Ocular manifestations | 15% |
| Hearing loss | 10% |
| Developmental delay / intellectual disability | 10% |
| Congenital heart defect | 6% |
| Gastrointestinal anomalies | 5% |
Percentages are calculated from the literature from 1927 to 2024 [Fiesco-Roa et al 2019, Hoover et al 2024]. Frequencies are approximate, since many reports did not mention physical descriptions.
Characteristic Physical Features
Characteristic physical features / congenital anomalies occur in approximately 75% of individuals with FA.
Growth deficiency. Approximately 40% of affected individuals are born small for gestational age [Giri et al 2018]. An additional 25% display growth deficiency over time. Height tends to be more consistently reported as below the reference population, with the average height in children 2.2 standard deviations (SD) below the mean and 2.0 SD below the mean in adults [Wajnrajch et al 2001, Giri et al 2007, Rose et al 2012]. Linear growth deficiencies have been attributed to combinations of endocrinopathies (growth hormone deficiency, hypogonadism, hypothyroidism), nutritional deficiencies, and poor bone health [Wajnrajch et al 2001, Giri et al 2007, Rose et al 2012, Petryk et al 2015, Koo et al 2023, Barbus et al 2024]. Endocrinopathy and skeletal impacts of treatment with hematopoietic stem cell transplantation (HSCT) can also impact linear growth if administered prior to closure of growth plates [Barnum et al 2016]. FA-specific growth charts by biologic sex have been developed [Barbus et al 2024].
Abnormal skin pigmentation is a common feature in individuals with FA. Café au lait macules and hypopigmented macules can be present at birth or develop over time, with café au lait macules typically developing prior to puberty. Skinfold freckle-like hyperpigmented macules arise around puberty [Giampietro et al 1993, Fiesco-Roa et al 2019, Kesici et al 2019, Ruggiero et al 2022, Altintas et al 2023].
Skeletal malformations of the upper limbs account for 70% of all skeletal anomalies in FA and can be unilateral or bilateral [Shimamura & Alter 2010].
Thumbs (35%). Absent, hypoplastic, bifid, duplicated, triphalangeal, long, and/or proximally placed
Radii (7%). Absent or hypoplastic (only with abnormal thumbs), absent or weak pulse
Hands (5%). Flat thenar eminence, absent first metacarpal, clinodactyly, and/or preaxial polydactyly
Ulnae (1%). Dysplastic and/or short
Skeletal malformations of lower limbs include the following:
Leg length discrepancy, syndactyly, polydactyly, short toes, and/or club feet
Congenital hip dislocation
Microcephaly (head circumference more than two 2 SD below the mean for age) can be present at birth or become apparent over time.
Genitourinary tract anomalies include the following:
Kidney anomalies (25%). Horseshoe, ectopic, pelvic, hypoplastic, dysplastic, or absent kidney; hydronephrosis or hydroureter
Males (25%). Hypospadias, micropenis, cryptorchidism, anorchia, hypo- or azoospermia, reduced fertility
Females (2%). Bicornuate or uterus malposition, small ovaries
Ocular manifestations include microphthalmia, cataracts, astigmatism, strabismus, epicanthal folds, hypotelorism, hypertelorism, and ptosis.
Other Common Clinical Features
Endocrine disorders. Endocrinopathies can develop in childhood in individuals with FA, and surveillance is recommended annually from time of diagnosis (see Fanconi Cancer Foundation Clinical Care Guidelines). Hypothyroidism (30%-60%), diabetes (8%-10%), hyperglycemia / impaired glucose tolerance (25%-70%), and insulin resistance have been reported [Petryk et al 2015]. Growth hormone deficiency and osteoporosis are also described. Endocrinopathies can also be caused or exacerbated by HSCT [Altintas et al 2023].
Hearing loss, when present, is usually conductive secondary to middle-ear bony anomalies with or without additional ear anomalies (e.g., dysplastic auricle, narrow ear canal, abnormal pinna). Sensorineural hearing loss has rarely been described. Hearing loss can be present at birth and is typically mild; however, hearing loss can be more severe, impact speech-language development, and benefit from amplification devices or technology. Hearing loss is not believed to be progressive in FA, though it can be impacted by infection or exposure to ototoxic medications [Kalejaiye et al 2016].
Developmental delay and/or intellectual disability is seen in 10% of individuals with FA but is not well described. Co-occurrence of hearing loss and microcephaly may be associated with a higher risk of developmental delay and/or intellectual disability. Most individuals (4/5) with RAD51-related FA are reported to have variable developmental delay, including speech and language delays, motor delays, and intellectual disability (mild to severe) [Altintas et al 2025].
Congenital heart defects and vascular anomalies include Patent ductus arteriosus, atrial septal defect, ventricular septal defect, coarctation of the aorta, truncus arteriosus, and situs inversus.
Gastrointestinal manifestations include esophageal, duodenal, or jejunal atresia, imperforate anus, tracheoesophageal fistula, annular pancreas, and malrotation.
Central nervous system findings have been seen on brain imaging (3%) and include small pituitary, pituitary stalk interruption syndrome, absent corpus callosum, cerebellar hypoplasia, hydrocephalus, and dilated ventricles [Johnson-Tesch et al 2017]. The progressive cerebrovascular anomaly of moyamoya disease has been described rarely in individuals with FA [Cohen et al 1980, Pavlakis et al 1995, Al-Hawsawi et al 2015, Zhu et al 2022, D'Incan 2025].
Other skeletal manifestations
Facial features (2%). Triangular face shape, micrognathia, mid-face hypoplasia
Spine anomalies (2%). Spina bifida, scoliosis, hemivertebrae, rib anomalies, coccygeal aplasia
Neck anomalies (1%). Sprengel deformity, Klippel-Feil anomaly, short or webbed neck, low hairline
Immune dysfunction. While not systematically studied to provide estimates of incidence, case series have identified reduced numbers and function of NK cells and reduced numbers of B cells [Korthof et al 2013, Myers et al 2017]. Increased risk for opportunistic infection or T-cell defects has not been described.
Bone Marrow Failure
The age of onset of bone marrow failure is highly variable, even among sibs. An analysis of 754 individuals enrolled in the International Fanconi Anemia Registry (IFAR) with pathogenic variants in FANCA, FANCC, and FANCG identified an average age of onset of bone marrow failure of 7.6 years [Kutler et al 2003]. Rarely, bone marrow failure can present in infants and small children [Shimamura & Alter 2010]. Individuals with FANCG- and FANCC-related FA have higher incidence and earlier presentation of bone marrow failure. For all forms of FA, the risk of developing any hematologic abnormality is 90% by age 40 years [Kutler et al 2003]. Registry data across the world are consistent in incidence and age of onset, even in more recent years [Risitano et al 2016, Altintas et al 2023].
Table 3.
Fanconi Anemia: Severity of Bone Marrow Failure
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| Hematopoietic Cell Affected | Mild | Moderate | Severe |
|---|
| Absolute neutrophil count | <1,500/mm3 | <1,000/mm3 | <500/mm3 |
| Platelet count | 50,000-150,000/mm3 | <50,000/mm3 | <30,000/mm3 |
| Hemoglobin level | ≥8 g/dL | <8 g/dL | <8 g/dL |
Cancer Susceptibility
Myeloid malignancy. Genome instability in FA commonly results in clonal hematopoiesis that may precede development of myelodysplastic syndrome (MDS) or acute myeloid leukemia (AML), though clonal hematopoiesis is not always a feature in aberrant myelopoiesis. Gains of chromosome 1q or 3q or deletions of chromosome 7 (up to full monosomy 7) predominate [Mehta et al 2010, Quentin et al 2011, Meyer et al 2012]. Chromosome 7 abnormalities can drive development of MDS and/or AML, as can gains of 3q when accompanied by other chromosomal alterations, and these chromosomal findings should prompt consideration of HSCT [Cioc et al 2010, Mehta et al 2010, Peffault de Latour & Soulier 2016]. Lower-risk clones demonstrating gains of 1q, loss of 20q, or loss of 6p should prompt close surveillance for resolution or evolution.
Recent longitudinal multiomic analysis of bone marrow and skin samples from 62 individuals with FA showed clonal expansion over time, with some developing MDS and/or AML [Sebert et al 2023]. Approximately half the cohort had 1q gains with duplication of MDM4, which encodes a negative regulator of tumor suppressor p53. MDM4 inhibition of p53 likely promoted leukemogenesis over apoptosis or bone marrow failure. Loss of tumor suppressor RUNX1 was also commonly acquired during clonal hematopoiesis progression in FA, often following chromosome 1, 3, or 7 abnormalities. Gains of chromosome 3q were shown to include the oncogene MECOM, driving leukemogenesis in some individuals.
The relative risk for MDS is approximately 6,000-fold and AML approximately 700-fold in individuals with FA compared to the general population [Alter 2014]. Risk for MDS and AML in FA must consider the competing risk of bone marrow failure. In competing risk analyses from IFAR, the National Cancer Institute (NCI) cohort, and the German FA registry, the cumulative incidence of MDS or AML by age 40 years was approximately 35% [Kutler et al 2003, Rosenberg et al 2008, Alter et al 2018]. Individuals with BRCA2-related FA have a uniquely high risk for AML in childhood, with an incidence of 80% by age ten years. However, hypomorphic BRCA2 variants are associated with onset of malignancy at a later age or not at all. BRCA2 pathogenic variants c.631+1G>A and c.631+2T>G are particularly deleterious, with myeloid malignancy arising before age three years [Alter 2014].
Solid tumors may be the first manifestation of FA in individuals who have no birth defects and have not experienced bone marrow failure.
Head and neck squamous cell carcinomas (HNSCCs) are the most common solid tumor in individuals with FA. The incidence is 500- to 1,000-fold higher than in the general population [
Rosenberg et al 2003,
Rosenberg et al 2005,
Alter et al 2018]. HSCT conditioning chemotherapy and/or radiation, mucositis, and graft-vs-host disease may contribute to higher rates of HNSCCs [
Socié et al 1998,
Ricci et al 2025]. FA-related HNSCCs show distinct differences from HNSCCs seen in the general population. FA-related HNSCCs:
Occur at an earlier age (age 20-40 years) than in the general population (age 60-70 years);
Most commonly occur in the oral cavity;
Present at an advanced stage;
Respond poorly to therapy.
Individuals with FA are at increased risk for second primary cancers of the skin and genitourinary tract. The pattern of second primaries resembles that observed in HPV-associated HNSCCs in the general population [
Kutler et al 2016].
BRCA2- and
PALB2-related FA due to complete
loss-of-function pathogenic variants are associated with an increased risk for brain tumors, kidney tumors, neuroblastoma, and breast cancer compared to other causes of FA. Note: Hypomorphic
BRCA2 pathogenic variants are associated with a lower risk of malignancy than
BRCA2 loss-of-function pathogenic variants.
Pathophysiology. Bone marrow failure in FA results from attrition of hematopoietic stem cells by apoptosis in response to DNA damage that FA cells lack the ability to adequately resolve. Contributing factors identified to date include DNA damage induced by oxidative stress and dysregulated protein homeostasis and unfolded protein toxicity converging on premature hematopoietic stem cell exhaustion [Du et al 2008, Rodríguez et al 2021, Kovuru et al 2024]. Activation of the tumor suppressor p53 pathway in the abnormal DNA damage response of FA provides protection against malignant transformation in hematopoietic cells, instead contributing to expedited stem cell attrition and bone marrow failure [Ceccaldi et al 2012].
Phenotype Correlations by Gene
BRCA2 pathogenic variants cause a near-universal risk of malignancy in early childhood (97% by age six years). Acute leukemia, often but not always AML, occurs in 80% by age ten years [Alter 2014]. Solid tumors of embryonic origin, including brain tumors, Wilms tumor, and neuroblastoma, are also common in individuals with BRCA2-related FA (affecting 10%-33%) and arise typically before age five years [Rosenberg et al 2003, Rosenberg et al 2005, Alter et al 2018, McReynolds et al 2021].
FANCB pathogenic variants have been shown to predominantly cause early-onset bone marrow failure (over myeloid malignancy) [Jung et al 2020].
PALB2 encodes an essential protein partner for BRCA2 as it interfaces with DNA. PALB2-related FA is associated with the same malignancy risks and early age of occurrence as BRCA2-related FA [McReynolds et al 2021].
RAD51. Most individuals (4/5) with RAD51-related FA are reported to have variable developmental delay, including speech and language delays, motor delays, and intellectual disability (mild to severe) [Altintas et al 2025].
Genotype-Phenotype Correlations
The clinical spectrum of FA remains heterogenous, though some genotype-phenotype correlations have been identified. In general, null variants lead to a more severe phenotype (e.g., congenital anomalies, early-onset bone marrow failure, and MDS/AML) than hypomorphic variants. A review of genotype-phenotype associations in FA is available [Fiesco-Roa et al 2019].
BRCA2. Specific splice site variants in intron 7 (e.g., c.631+1G>A and c.631+2T>G) offer the greatest risk of AML, with all homozygotes and compound heterozygotes developing AML by age three years [Alter 2006, Alter 2014].
FANCA. Conflicting reports have associated [Faivre et al 2000] and refuted association [Castella et al 2011] of homozygous FANCA null pathogenic variants with earlier-onset anemia and higher incidence of leukemia than individuals with pathogenic variants that permit production of an abnormal FANCA protein. Other FANCA variants (p.His913Pro, p.Arg951Gln, p.Arg951Trp) have been associated with slower hematologic disease progression [Bottega et al 2018]. In an effort to elucidate the impact of specific pathogenic variants, the NCI group identified a higher frequency of solid tumors in individuals with FANCA pathogenic variants in the exon 27-30 C-terminal domain. This region is functionally critical for localization of FANCA to the nucleus. In their cohort, individuals with heterozygous or biallelic pathogenic variants in exon 27-30 of FANCA had a dramatic increase in solid tumor incidence starting around age 20 years and reaching nearly 100% by age 45 years (compared to 25%-50% solid tumor incidence in individuals with other FANCA pathogenic variants) [Altintas et al 2023].
FANCB. Approximately 80% of males with truncating/null FANCB pathogenic variants present with a VACTERL-H (vertebral, anal, cardiac, tracheoesophageal fistula, renal, limb anomalies, hydrocephalus) phenotype, resulting in FANCB-related FA having the highest rate of congenital anomalies. A PHENOS (skin pigmentation, small head, small eyes, nervous system, otic anomalies, short stature) phenotype is apparent in an additional ~5% of males with a null FANCB pathogenic variant [Fiesco-Roa et al 2019]. Research studies of specific FANCB pathogenic variants revealed that pathogenic variants resulting in protein truncation are associated with more severe clinical disease than FANCB missense pathogenic variants, which maintain residual activity and function [Jung et al 2020].
FANCC. Bone marrow failure in FANCC-related FA has been identified as having higher incidence at earlier ages compared to FANCA- or FANCG-related FA in US data, but with a less severe phenotype in a European report [Faivre et al 2000, Rosenberg et al 2008, Yabe et al 2019, Alter et al 2022]. Perhaps such differences are variant specific, with more severe disease caused by some (c.456+4A>T, p.Arg548Ter, and p.Leu554Pro) [Faivre et al 2005] and less severe disease caused by others (c.165+1G>T) [Hartmann et al 2010]. Further genetic modifiers may influence phenotypes among individuals of different ethnicities (e.g., milder phenotype was reported among Japanese individuals homozygous for FANCC pathogenic variant c.456+4A>T) [Futaki et al 2000].