Fanconi Anemia

CLINICAL CHARACTERISTICS

Fanconi anemia (FA) is characterized by physical abnormalities, bone marrow failure, and increased risk for malignancy. Physical abnormalities, present in approximately 75% of affected individuals, include one or more of the following: short stature, abnormal skin pigmentation, skeletal malformations of the upper and/or lower limbs, microcephaly, and ophthalmic and genitourinary tract anomalies. Progressive bone marrow failure with pancytopenia typically presents in the first decade, often initially with thrombocytopenia or leukopenia. The incidence of acute myeloid leukemia is 13% by age 50 years. Solid tumors – particularly of the head and neck, skin, and genitourinary tract – are more common in individuals with FA.

DIAGNOSIS/TESTING: The diagnosis of FA is established in a proband with increased chromosome breakage and radial forms on cytogenetic testing of lymphocytes with diepoxybutane (DEB) and mitomycin C (MMC) and/or one of the following identified on molecular genetic testing: biallelic pathogenic variants in one of the 21 genes known to cause autosomal recessive FA; a heterozygous pathogenic variant in known to cause autosomal dominant FA; or a hemizygous pathogenic variant in known to cause X-linked FA.

MANAGEMENT

Administration of oral androgens (e.g., oxymetholone) improves blood counts (red cell and platelets) in approximately 50% of individuals with FA; granulocyte colony-stimulating factor improves the neutrophil count in some individuals; hematopoietic stem cell transplantation (HSCT) is the only curative therapy for the hematologic manifestations of FA, but the high risk for solid tumors remains and may even be increased in those undergoing HSCT. All these treatments have potential significant toxicity. early detection and surgical removal remains the mainstay of therapy for solid tumors. Treatment of growth deficiency, limb anomalies, ocular anomalies, renal malformations, genital anomalies, hypothyroidism, cardiac anomalies, and dermatologic manifestations as recommended by the subspecialty care provider. Hearing aids may be helpful for hearing loss as per otolaryngologist; supplemental feeding as needed by nasogastric tube or gastrostomy; vitamin D supplementation; early intervention for developmental delays; individualized education plan for school-age children; speech, occupational, and physical therapy as needed; liberal use of sunscreen and rash guards; social work and care coordination as needed. Human papilloma virus (HPV) vaccination to reduce the risk for gynecologic cancer in females, and possibly reduce the risk of oral cancer in all individuals. T-cell depletion of the donor graft to minimize the risk of graft-vs-host disease; conditioning regimen without radiation prior to HSCT to reduce the subsequent risk of developing solid tumors. Clinical assessment of growth, feeding, nutrition, spine, and ocular issues at each visit throughout childhood. Annual ophthalmology examination; annual evaluation with endocrinologist including TSH, free T4, 25-hydroxy vitamin D, two-hour glucose tolerance testing, and insulin levels; assessment of pubertal stage and hormone levels at puberty and every two years until puberty is complete; follow up hearing evaluation if exposed to ototoxic drugs; annual developmental assessment; blood counts every three to four months or as needed; bone marrow aspirate and biopsy to evaluate morphology and cellularity, FISH and cytogenetics to evaluate for emergence of a malignant clone at least annually after age two years; liver function tests every three to six months and liver ultrasound examination every six to twelve months in those receiving androgen therapy; gynecologic assessment for genital lesions annually beginning at age 13 years; vulvo-vaginal examinations and Pap smear annually beginning at age 18 years; oral examinations for tumors every six months beginning at age nine to ten years; annual nasolaryngoscopy beginning at age ten years; dermatology evaluation every six to 12 months; annual abdominal ultrasound and brain MRI in those with -related FA. Additional cancer surveillance for individuals with , , , and related FA. Transfusions of red cells or platelets for persons who are candidates for HSCT; family members as blood donors if HSCT is being considered; blood products that are not filtered (leukodepleted) or irradiated; toxic agents that have been implicated in tumorigenesis; unsafe sex practices, which increase the risk of HPV-associated malignancy; excessive sun exposure. Radiographic studies solely for the purpose of surveillance (i.e., in the absence of clinical indications) should be minimized. DEB/MMC testing or molecular genetic testing (if the family-specific pathogenic variants are known) of all sibs of a proband for early diagnosis, treatment, and monitoring for physical abnormalities, bone marrow failure, and related cancers.

GENETIC COUNSELING

Fanconi anemia (FA) can be inherited in an autosomal recessive manner, an autosomal dominant manner (-related FA), or an X-linked manner (-related FA). Each sib of an affected individual has a 25% chance of inheriting both pathogenic variants and being affected, a 50% chance of inheriting one pathogenic variant and being a heterozygote, and a 25% chance of inheriting neither of the familial FA-related pathogenic variants. Heterozygotes are not at risk for autosomal recessive FA. However, heterozygous mutation of a subset of FA-related genes (e.g., , , , and ) is associated with an increased risk for breast and other cancers. Given that all affected individuals with -related FA reported to date have the disorder as a result of a pathogenic variant, the risk to other family members is presumed to be low. For carrier females the chance of transmitting the pathogenic variant in each pregnancy is 50%; males who inherit the pathogenic variant will be affected; females who inherit the pathogenic variant will be carriers and will usually not be affected. Carrier testing for at-risk relatives (for autosomal recessive and X-linked FA) and prenatal and preimplantation genetic testing are possible if the pathogenic variant(s) in the family are known.