In 1927 Fanconi described a familial form of aplastic ane- mia in three brothers with short stature, hypogonadism and skin pigmentation. The incidence of Fanconi anemia (FA) is esti- mated to be 1 in 360,000 births. The carrier frequency is esti- mated as 1 in 300 in Europe and the United States. Founder mutations have been described in Ashkenazi Jews, who have carrier frequency of 1 in 89.
GENETICS/BASIC DEFECTS
1. Inheritance
a. Autosomal recessive
b. Genetically and phenotypically heterogeneous 2. Presence of at least 11 complementation groups delineat-
ed by cell fusion studies a. FA-A (65–70%) b. FA-B (<2%) c. FA-C (10–15%) d. FA-D1
e. FA-D2 f. FA-E (2–5%) g. FA-F (<2%) h. FA-G (10%)
i. FA-I j. FA-J k. FA-L
3. Eight FA genes have been identified by complementation cloning or by positional cloning techniques:
a. FANCA, mapped to 16q24.3 b. FANCB, mapped to 13q12.3 c. FANCC, mapped to 9q22.3 d. FANCD1, mapped to 13q12.3 e. FANCD2, mapped to 3p25.3
f. FANCE, mapped to 6p21.22 g. FANCF, mapped to 11p15 h. FANCG, mapped to 9p13
4. A candidate-gene approach leads to the breast cancer sus- ceptibility gene BRCA2 as the gene defective in FA-D1 patients. The Fanconi-BRCA pathway is activated in response to certain kinds of DNA damage, particularly DNA agents that cause double-strand breaks in DNA such as ultraviolet light, ionizing radiation, and cisplatin 5. FA cells are hypersensitive to cross-linking agents such as
diepoxybutane (DEB), nitrogen mustard (NTM) and mit- omycin C (MMC): induction of chromosomal aberrations (breaks and rearrangements)
6. Reverse mosaicism
a. Not infrequent in Fanconi anemia
b. Presence of two populations of lymphocytes in mosaic Fanconi anemia patients
i. One being hypersensitive to the clastogen ii. The other normal
c. Phenotypic reversion to normal
i. Correlated with intragenic homologous recom- bination in compound heterozygous patients giving rise to the segregation of a wild type allele at the disease locus
ii. The resulting cells are thus essentially cured from the disease
iii. Progeny from a reverted stem cell expected to have a proliferative advantage over affected cells and thus may gradually expand and take over hematopoiesis
d. Patients with a high proportion of reverted cells may be falsely diagnosed as negatives
7. Defective FA functional pathway a. Defective DNA repair
b. Prolonged G2/M transition in the cell cycle c. Increased oxygen sensitivity
d. Abnormally regulated apoptosis and accelerated telomere shortening
e. Defective hemopoiesis
CLINICAL FEATURES
1. Variable clinical expression and severity
2. Hematological abnormalities secondary to bone marrow failure (>90%)
a. Clinical hallmark of Fanconi anemia b. Usually starting in childhood
c. Increased incidence of aplastic anemia, myelodys- plastic syndrome, and acute myeloid leukemia d. Initial presentation
i. Pallor ii. Bleeding
iii. Recurrent infections
e. Thrombocytopenia or leukopenia typically preceding anemia
f. Severe progressive pancytopenia due to loss of hematopoietic stem cells: the cardinal clinical feature g. Increased risk of infections due to neutropenia h. Sweet syndrome (neutrophilic skin infiltration)
reported in a few patients with Fanconi anemia and myelodysplastic syndrome
3. Diverse congenital abnormalities (>63%) a. Growth retardation
b. Short stature (60%)
c. Upper limb anomalies (50%)
i. Mainly radius and thumb abnormalities
a) Absent, hypoplastic, or supernumerary thumbs with hypoplastic thenar eminence
b) Absent, hypoplastic radii and ulnae associated with abnormal thumbs
c) Absent first metacarpal
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ii. Clinodactyly iii. Polydactyly
iv. Short fingers
v. Transverse palmar crease d. Other skeletal abnormalities
i. Short webbed neck with low hairline ii. Spine anomalies
a) Spina bifida b) Scoliosis
c) Sacrococcygeal sinus d) Other vertebral anomalies iii. Lower limb anomalies
a) Toe syndactyly b) Pes planus c) Abnormal toes
d) Congenital hip dislocation e. Skin pigmentary changes (65%)
i. Generalized hyperpigmentation ii. Café au lait spots
iii. Hypopigmentation f. Eye anomalies (25%)
i. Microphthalmia ii. Strabismus iii. Epicanthal folds
iv. Hypertelorism/hypotelorism v. Ptosis
vi. Cataracts vii. Epiphora viii. Nystagmus g. Ear anomalies (10%)
i. Deafness, usually conductive secondary to middle ear abnormalities
ii. Abnormal pinna
iii. Stenosis or atresia of the external auditory meatus
iv. Low-set ears h. Heart disease
i. Congenital heart disease a) Patent ductus arteriosus b) Ventricular septal defect c) Pulmonary stenosis d) Aortic coarctation ii. Cardiomyopathy i. Renal anomalies (25%)
i. Kidney a) Pelvic kidneys b) Horseshoe kidneys
c) Hypoplastic/dysplastic kidneys
ii. Collecting system (hydronephrosis, hydroureter, reflux)
iii. Abnormal artery j. Gastrointestinal problems
i. Atresia a) Esophagus b) Duodenum c) Jejunum
ii. Tracheoesophageal fistula iii. Anteriorly placed anus
iv. Imperforate anus v. Persistent cloaca
vi. Meckel diverticulum vii. Umbilical hernia viii. Abnormal biliary ducts
ix. Megacolon
x. Abdominal diastasis xi. Budd-Chiari syndrome xii. Annular pancreas k. CNS abnormalities
i. Microcephaly ii. Hydrocephalus
iii. Absent septum pellucidum iv. Neural tube defects l. Hypogonadism in males
i. Underdeveloped gonads ii. Cryptorchidism
iii. Hypospadias
iv. Defective spermatogenesis (infertility)
v. A few males with Fanconi anemia fathered children
m. Hypogonadism in females i. Hypogenitalia ii. Bicornuate uterus iii. Absent uterus or vagina
iv. Ovarian atresia v. Delayed menarche vi. Irregular menses vii. Early menopause
viii. Successful pregnancies with liveborn children observed
n. Absence of obvious congenital abnormalities in approximately 33% of patients with Fanconi anemia 4. Predisposition to malignancy
a. Hematologic tumors (60%)
i. Acute myelogenous leukemia (30%) ii. Myelodysplastic syndrome (26%) iii. Acute lymphocytic leukemia
iv. CMMOL
v. Burkitt lymphoma b. Nonhematologic tumors (40%)
i. Liver tumors (9%) a) Adenoma
b) Hepatocellular carcinoma c) Adenocarcinoma
ii. Brain tumor (2%) a) Medulloblastoma b) Astrocytomas iii. Renal tumors (3%)
a) Wilm tumor
b) Renal cell carcinoma c) Nephroblastoma
iv. Squamous cell carcinoma (20%) a) Head and neck
b) Vulvar c) Cervix d) Cutaneous e) Anus f) Esophagus
v. Miscellaneous tumors (6%) a) Breast carcinoma b) Basal cell carcinoma
c) Neuroblastoma d) Desmoid tumor e) Gonadoblastoma
f) Melanoma g) Neurilemmoma h) Osteogenic sarcoma
5. Cumulative probability of developing leukemia, liver tumors, and solid tumors in FA patients
a. Close to 40% by age 30 b. About 50% by age 45
c. An astounding 76% by age 45 6. Prognosis
a. Mean survival: 16 years b. Main causes of death
i. Pancytopenia which develops in the first decade of life
ii. Associated progressive microcytosis
iii. Extremely high probability of developing bone marrow failure
iv. A predisposition to malignancy, particularly acute myeloid leukemia and aplastic anemia
7. Differential diagnosis
a. VATER/VACTERL association overlap with FA i. Vertebral defects
ii. Tracheo-esophageal atresia iii. Renal defects
iv. Radial ray defects b. Diamond-Blackfan anemia
i. Defective erythroid progenitor maturation ii. Normochromic or macrocytic anemia
iii. Congenital malformations in over one third of patients
a) Head (micrognathia, cleft lip) b) Upper limb defects
c) Genitourinary anomalies iv. A heterogeneous disorder
a) Sporadic in most cases
b) Autosomal dominant in some cases c) Rarely autosomal recessive inheritance c. Nijmegen breakage syndrome
i. A rare autosomal recessive disorder
ii. Resulting from mutations in NBS1 which codes for the nibrin protein
iii. Clinical characteristics a) Immune deficiency b) Microcephaly
c) Hypersensitivity to ionizing radiation d. Other chromosomal breakage syndromes (Bloom
syndrome, ataxia-telangiectasia)
i. Also exhibit high rates of spontaneous chromo- somal breakage
ii. Only FA cells exhibit increased chromosomal breakage in response to DEB
DIAGNOSTIC INVESTIGATIONS
1. Difficult to diagnose FA because of phenotypic diversity 2. Hematologic investigation
a. Progressive decrease in peripheral blood counts, often present by 7–8 years of age
i. Thrombocytopenia ii. Leukopenia iii. Anemia
b. Macrocytic red blood cells, often with increased fetal hemoglobin
c. Generally increased serum erythropoietin concentration d. Hypocellular or dysplastic bone marrow
e. Bone marrow failure with pancytopenia
f. Bone marrow cytogenetic testing: Cytogenetic abnor- malities may progress to leukemia or myelodysplastic syndrome
3. DEB testing
a. 10- to 100-fold increased chromosomal breakage (breaks, rearrangements, radials, exchanges) of Fanconi anemia cells after incubation of the patient’s cells with chemical clastogen, DEB
b. Highly sensitive and specific test for Fanconi anemia c. Allowing diagnosis of Fanconi anemia in persons with diverse clinical features including those without clinically detectable congenital abnormalities d. Used successfully in prenatal diagnosis of Fanconi
anemia
e. Remains underutilized mainly because there are some clinical conditions in which FA is not usually suspected f. Disadvantage
i. Requires a high degree of cytogenetic expertise and meticulous attention to cell culture and safety conditions
ii. Fails to distinguish among Fanconi anemia patients in different complementation groups iii. Fails to identify heterozygote carriers of mutant
Fanconi anemia genes 4. Cell cycle test
a. Alternative to cytogenetic testing
b. Diagnostic potential of the cell cycle test for Fanconi anemia
c. Based on the observation that Fanconi anemia cells experience difficulties in traversing the S and G2 compartment of the cell cycle
d. Limitation of cell cycle test
i. Applicable only to nonleukemic cells
ii. Confirmatory DEB studies required in cases with evidence for G2-phase arrest
5. Molecular genetic testing
a. Complicated by the presence of at least eleven com- plementation groups
b. Direct sequence analysis not clinically available because of the following reasons:
i. The number of possible affected genes
ii. The large number of possible mutations in each gene
iii. The large size of many of the Fanconi anemia genes
c. Identification of “common” mutant alleles of the FANCA, FANCC, FANCF, and FANCG genes d. Linkage analysis once a family has been assigned to
a complementation group by a functional assay or by the detection of a specific mutant allele using highly polymorphic microsatellite markers located in close proximity to both FAA and FAAC genes
i. Used for carrier detection ii. Used for prenatal diagnosis 6. Cancer surveillance
a. Annual bone marrow examination provides early evi- dence for myelodysplastic syndrome or leukemia
i. Aspirate for cell types ii. Biopsies for cellularity iii. Cytogenetics
b. Liver function tests and ultrasound examinations to identify adenomas or hepatomas before becoming symptomatic
c. Screening for solid tumors: more complex because of multiplicity of cancer types
i. Direct visualization of the oropharynx and fiberoptic endoscopy for screening for aerodi- gestive cancers and precancerous lesions ii. Gynecologic examinations for vulvar and cervical
tumors beginning with menarche
GENETIC COUNSELING
1. Recurrence risk a. Patient’s sib
i. 25% chance of inheriting both mutation alleles and being affected
ii. 2/3 chance of being carriers in unaffected sibs who have a normal DEB test
b. Patient’s offspring: recurrence risk not increased unless the spouse is a carrier, in which case 50% of offspring will be affected; otherwise all offspring of the affected parent will be carriers who will be asymptomatic
2. Prenatal diagnosis
a. Prenatal ultrasonography to evaluate fetal anomalies consistent with FA
b. Prenatal diagnosis available to at-risk families by CVS, amniocentesis or cordocentesis
i. Demonstration of chromosome instability by DEB test
ii. Molecular genetic testing of FA gene mutations if the disease-causing mutations are previously characterized in a given family
iii. Preimplantation genetic diagnosis possible by using molecular methods, resulting in implanta- tion of an embryo without FA mutations 3. Management
a. Supportive care
i. Developmental assessment
ii. HLA typing of the patient, sibs, and parents in anticipation of possible bone marrow transplan- tation
iii. Full blood typing
iv. Packed red blood cells transfusions for sympto- matic anemia
v. Platelet transfusions for symptomatic thrombo- cytopenia
vi. Antimicrobials for secondary infections b. Surgical care
i. Splinting and hand surgery indicated for thumb and radial anomalies
ii. Surgery for congenital heart defects and gas- trointestinal anomalies such as TE fistula c. Transient response
i. Androgens (oxymetholone) shown to improve the blood counts in approximately 50% of patients
ii. Corticosteroids iii. Cytokines
iv. Granulocyte-macrophage colony-stimulating factor and granulocyte colony-stimulating factor (shown to improve the neutrophil count in some patients) for symptomatic neutropenia
d. Hematopoietic stem cell transplantation may cure aplastic anemia and prevent myelodysplastic syndrome or leukemia
i. Peripheral blood stem cells
ii. Allogenic bone marrow transplant with a histo- compatible sibling donor: treatment of choice iii. Umbilical cord blood offers a potential source of
hematopoiesis stem cells for Fanconi anemia patients without sibling matches
e. Successful transplantation obtained by using in vitro fertilization and preimplantation genetic diagnosis of hematopoietic stem cells from a donor selected on the basis of specific, desirable disease and HLA characteristics
i. Select embryos which are HLA-identical to the patient and unaffected by FA for intrauterine transfer and let the pregnancy continue to term ii. Obtain the umbilical cord blood from the healthy
newborn infant and use it as the source of HLA- identical hematopoietic stem cells to reconstitute normal hematopoiesis in the affected sibling f. Follow up surveillance for solid malignancies g. Gene therapy not currently available
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Fig. 1. A young boy with Fanconi anemia showing pallor and radial ray defects of the upper extremities.
Fig. 2. An adolescent girl with Fanconi anemia showing similar phenotype.
