Hematological consequences of a FANCG founder mutation in Black South African patients with Fanconi anemia

Fanconi anemia: current insights regarding epidemiology, cancer, and DNA repair

Fanconi anemia is a genetic disorder that is characterized by bone marrow failure, as well as a predisposition to malignancies including leukemia and squamous cell carcinoma (SCC). At least 22 genes are associated with Fanconi anemia, constituting the Fanconi anemia DNA repair pathway. This pathway coordinates multiple processes and proteins to facilitate the repair of DNA adducts including interstrand crosslinks (ICLs) that are generated by environmental carcinogens, chemotherapeutic crosslinkers, and metabolic products of alcohol. ICLs can interfere with DNA transactions, including replication and transcription. If not properly removed and repaired, ICLs cause DNA breaks and lead to genomic instability, a hallmark of cancer. In this review, we will discuss the genetic and phenotypic characteristics of Fanconi anemia, the epidemiology of the disease, and associated cancer risk. The sources of ICLs and the role of ICL-inducing chemotherapeutic agents will also be discussed. Finally, we will review the detailed mechanisms of ICL repair via the Fanconi anemia DNA repair pathway, highlighting critical regulatory processes. Together, the information in this review will underscore important contributions to Fanconi anemia research in the past two decades.

A comprehensive molecular study identified 12 complementation groups with 56 novel FANC gene variants in Indian Fanconi anemia subjects

Fanconi anemia (FA) is a rare autosomal or X-linked genetic disorder characterized by chromosomal breakages, congenital abnormalities, bone marrow failure (BMF), and cancer. There has been a discovery of 22 FANC genes known to be involved in the FA pathway. This wide number of pathway components makes molecular diagnosis challenging for FA. We present here the most comprehensive molecular diagnosis of FA subjects from India. We observed a high frequency (4.42 ± 1.5 breaks/metaphase) of chromosomal breakages in 181 FA subjects. The major clinical abnormalities observed were skin pigmentation (70.2%), short stature (46.4%), and skeletal abnormalities (43.1%), along with a few minor clinical abnormalities. The combination of Sanger sequencing and Next Generation Sequencing could molecularly characterize 164 (90.6%) FA patients and identified 12 different complementation groups [FANCA (56.10%), FANCG (16.46%), FANCL (12.80%), FANCD2 (4.88%), FANCJ (2.44%), FANCE (1.22%), FANCF (1.22%), FANCI (1.22%), FANCN (1.22%), FANCC (1.22%), FANCD1 (0.61%) and FANCB (0.61%)]. A total of 56 novel variants were identified in our cohort, including a hotspot variant: a deletion of exon 27 in the FANCA gene and a nonsense variant at c.787 C>T in the FANCG gene. Our comprehensive molecular findings can aid in the stratification of molecular investigation in the diagnosis and management of FA patients.

Endocrine profiling in patients with Fanconi anemia, homozygous for a FANCG founder mutation

BACKGROUND

Fanconi anemia (FA) is phenotypically diverse, hereditary condition associated with bone marrow failure, multiple physical abnormalities, and an increased susceptibility to the development of malignancies. Less recognized manifestations of FA include endocrine abnormalities. International discourse has highlighted that these abnormalities are widespread among children and adults with FA. To date there has been no systematic study that has evaluated the endocrine abnormalities in a cohort of patients with FA, homozygous for a founder mutation (c.637_643del (p.Tyr213Lysfs*6)) in FANCG. The objectives of the study were to evaluate endocrine gland function in patients with FA of a single FA genotype, and to determine the frequency and nature of endocrine abnormalities in this group.

METHODS

Cross-sectional, descriptive study of 24 South African patients of African ancestry with FA (homozygous for a FANCG founder mutation). Outcomes measured included growth, pubertal status, growth hormone axis screening, thyroid gland function, glucose and insulin metabolism and bone age (BA).

RESULTS

Endocrine dysfunction was present in 70.8% (17 of 24), including abnormal insulin-like growth factor 1 (IGF-1)/insulin-like growth factor-binding protein 3 (IGFBP-3) in 25.0% (6 of 24), insulin resistance in 41.7% (10 of 24), abnormal thyroid function in 16.7% (4 of 24) and short stature in 45.8% (11 of 24). No abnormalities of glucose metabolism were identified. Abnormal pubertal status was seen in three males (12.5%). Abnormal BAs were present in 34.8% (8 of 23).

CONCLUSION

Endocrine abnormalities occur at a high frequency in patients with FA, homozygous for a FANCG founder mutation, similar to other FA cohorts. Our data are specific to FA patients with a single genotype, and therefore provide the first genotype-phenotype information on endocrine abnormalities in South African patients, homozygous for a FANCG founder mutation. Recommendations regarding endocrine screening in this patient subgroup are made, including, but not limited to, baseline testing of thyroid function, fasted insulin and glucose, and IGF-1 and IGFBP-3.

Common and Founder Mutations for Monogenic Traits in Sub-Saharan African Populations

This review highlights molecular genetic studies of monogenic traits where common pathogenic mutations occur in black families from sub-Saharan Africa. Examples of founder mutations have been identified for oculocutaneous albinism, cystic fibrosis, Fanconi anemia, and Gaucher disease. Although there are few studies from Africa, some of the mutations traverse populations across the continent, and they are almost all different from the common mutations observed in non-African populations. Myotonic dystrophy is curiously absent among Africans, and nonsyndromic deafness does not arise from mutations in GJB2 and GJB7. Locus heterogeneity is present for Huntington disease, with two common triplet expansion loci in Africa, HTT and JPH3. These findings have important clinical consequences for diagnosis, treatment, and genetic counseling in affected families. We currently have just a glimpse of the molecular etiology of monogenic diseases in sub-Saharan Africa, a proverbial “ears of the hippo” situation.

Biallelic BRCA2 mutations in two black South African children with Fanconi anaemia

Fanconi anaemia (FA) is a genotypically and phenotypically heterogeneous genetic condition, characterized cytogenetically by chromosomal instability and breakage secondary to impaired DNA repair mechanisms. Affected individuals typically manifest growth restriction and congenital physical abnormalities and most progress to hematological disease including bone marrow aplasia. A rare genetic subtype of FA (FA-D1) is caused by biallelic mutations in the BRCA2 gene. Affected individuals manifest severe congenital anomalies and significant pigmentary changes and are additionally at risk for early onset leukemia and certain solid organ malignancies, including Wilms tumors and brain tumors. Parents of affected individuals are obligate carriers for heterozygous BRCA2 mutations and are thus potentially at risk for adult onset cancers which fall within the hereditary breast and ovarian cancer spectrum. We present two cases of black South African patients with FA diagnosed with biallelic BRCA2 mutations and discuss the phenotypic consequences and implications for them and their families. Recognition of this severe end of the phenotypic spectrum of FA is critical in allowing for confirmation of the diagnosis as well as cascade screening and appropriate care of family members.

Screening for mutations in two exons of FANCG gene in Pakistani population

BACKGROUND

Fanconi anemia is a rare autosomal recessive disorder of genetic instability. It is both molecularly and clinically, a heterogeneous disorder. Its incidence is 1 in 129,000 births and relatively high in some ethnic groups. Sixteen genes have been identified among them mutations in FANCG gene are most common after FANCA and FANCC gene mutations.

OBJECTIVE

To study mutations in exon 3 and 4 of FANCG gene in Pakistani population.

METHODS

Thirty five patients with positive Diepoxybutane test were included in the study. DNA was extracted and amplified for exons 3 and 4. Thereafter Sequencing was done and analyzed for the presence of mutations.

RESULTS

No mutation was detected in exon 3 whereas a carrier of known mutation c.307+1 G>T was found in exon 4 of the FANCG gene.

CONCLUSION

Absence of any mutation in exon 3 and only one heterozygous mutation in exon 4 of FANCG gene points to a different spectrum of FA gene pool in Pakistan that needs extensive research in this area.

Role of Genetic Factors in the Pathogenesis of Radial Deficiencies in Humans

Radial deficiencies (RDs), defined as under/abnormal development or absence of any of the structures of the forearm, radial carpal bones and thumb, occur with a live birth incidence ranging from 1 out of 30,000 to 1 out 6,000 newborns and represent about one third/one fourth of all the congenital upper limb anomalies. About half of radial disorders have a mendelian cause and pattern of inheritance, whereas the remaining half appears sporadic with no known gene involved. In sporadic forms certain anomalies, such as thumb or radial hypoplasia, may occur either alone or in association with systemic conditions, like vertebral abnormalities or renal defects. All the cases with a mendelian inheritance are syndromic forms, which include cardiac defects (in Holt-Oram syndrome), bone marrow failure (in Fanconi anemia), platelet deficiency (in thrombocytopenia-absent-radius syndrome), ocular motility impairment (in Okihiro syndrome). The genetics of radial deficiencies is complex, characterized by genetic heterogeneity and high inter- and intra-familial clinical variability: this review will analyze the etiopathogenesis and the genotype/phenotype correlations of the main radial deficiency disorders in humans.