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.

Nitric oxide synthase-2 (NOS2) gene polymorphism c.1832C>T (Ser608Leu) associated with nitrosative stress in Fanconi anaemia.

Fanconi anemia (FA) occurs due to genomic instability with predisposition to bone marrow failure, phenotypic abnormalities and cancers. Though mutations in 22 genes leading to DNA repair defect have been identified, the cellular factor such as oxidative stress has also shown to be associated with FA. Nitrosative Stress (NS) is biochemically correlated to many oxidative stress related disorders and the NS as a pathological hallmark in FA has been so far overlooked. We carried out the study first time in Indian patients with FA with an objective to understand the role of NS in the pathogenesis of FA. The study was carried out in 70 FA subjects. The FA subjects were diagnosed by chromosomal breakage analysis. Molecular study was carried out by Next Generation Sequencing and Sanger sequencing. The 3-nitrotyrosine [3-NT] levels were estimated through enzyme-linked immuno-sorbent assay (ELISA) and the nitric oxide synthase genes- NOS1 (c.-420-34221G>A (rs1879417), c.-420-10205C>T (rs499776), c.4286+720G>C (rs81631)) and NOS2 (c.1823C>T (p. Ser608Leu) (rs2297518)) polymorphism were studied by direct sequencing. Chromosomal breakage analysis revealed a high frequency of chromosomal breaks (Mean chromosomal breakage-4.13 ± 1.5 breaks/metaphase) in 70 FA patients as compared to the control. Molecular studies revealed FANCA (58.34%), FANCG (18.34%) and FANCL (16.6%) complementation groups. The 3-nitrotyrosine [3-NT] levels showed to be significantly (p < 0.05) elevated in FA subjects when compared to the age match controls. Genotyping of the NOS2 gene c.1823C>T (p. Ser608Leu) (rs2297518), showed statistically significant (P < 0.05) association with FA. Elevated level of 3-NT is one of the cause of NS and NOS2 gene polymorphism associated with FA is an important target in the treatment regimen.

Mitochondrial DNA variations and mitochondrial dysfunction in Fanconi anemia.

In-vitro studies with different Fanconi anemia (FA) cell lines and FANC gene silenced cell lines indicating involvement of mitochondria function in pathogenesis of FA have been reported. However, in-vivo studies have not been studied so far to understand the role of mitochondrial markers in pathogenesis of FA. We have carried out a systematic set of biomarker studies for elucidating involvement of mitochondrial dysfunction in disease pathogenesis for Indian FA patients. We report changes in the mtDNA number in 59% of FA patients studied, a high frequency of mtDNA variations (37.5% of non-synonymous variations and 62.5% synonymous variations) and downregulation of mtDNA complex-I and complex-III encoding genes of OXPHOS (p<0.05) as strong biomarkers for impairment of mitochondrial functions in FA. Deregulation of expression of mitophagy genes (ATG; p>0.05, Beclin-1; p>0.05, and MAP1-LC3, p<0.05) has also been observed, suggesting inability of FA cells to clear off impaired mitochondria. We hypothesize that accumulation of such impaired mitochondria in FA cells therefore may be the principal cause for bone marrow failure (BMF) and a plausible effect of inefficient clearance of impaired mitochondria in FA.

A founder variant in the South Asian population leads to a high prevalence of FANCL Fanconi anemia cases in India.

Fanconi anemia (FA) is a rare genetic disorder characterized by bone marrow failure, predisposition to cancer, and congenital abnormalities. FA is caused by pathogenic variants in any of 22 genes involved in the DNA repair pathway responsible for removing interstrand crosslinks. FANCL, an E3 ubiquitin ligase, is an integral component of the pathway, but patients affected by disease-causing FANCL variants are rare, with only nine cases reported worldwide. We report here a FANCL founder variant, anticipated to be synonymous, c.1092G>A;p.K364=, but demonstrated to induce aberrant splicing, c.1021_1092del;p.W341_K364del, that accounts for the onset of FA in 13 cases from South Asia, 12 from India and one from Pakistan. We comprehensively illustrate the pathogenic nature of the variant, provide evidence for a founder effect, and propose including this variant in genetic screening of suspected FA patients in India and Pakistan, as well as those with ancestry from these regions of South Asia.

Characterization of two novel FANCG mutations in Indian Fanconi anemia patients.

FA is a rare recessive genetic disorder with autosomal or X-linked mode of inheritance and is associated with 19 different FA complementation groups. We have studied three patients clinically diagnosed as FA. All three patients showed a high frequency chromosomal breakage in MMC induced blood cultures and FANCD2 non-monoubiquitination by western blotting. The molecular analysis using direct sequencing revealed two novel mutations in FANCG; 2 novel mutations c.1143+5G>C and c.883dupG, and a reported mutation c.1471_1473delAAAinsG. We have for the first time modeled FANCG protein with fold based template search using pGenthreader which revealed sequence fold identical to super helical TPR domain of O linked GLCNAC transferase and have studied the impact of mutations on the function and structure of FANCG. All three mutations are potential pathogenic molecular changes which can affect FANCG interactions required for FA pathway, homologous recombination repairs and unhooking step of the ICL repair process.

FANCA Gene Mutations with 8 Novel Molecular Changes in Indian Fanconi Anemia Patients.

Fanconi anemia (FA), a rare heterogeneous genetic disorder, is known to be associated with 19 genes and a spectrum of clinical features. We studied FANCA molecular changes in 34 unrelated and 2 siblings of Indian patients with FA and have identified 26 different molecular changes of FANCA gene, of which 8 were novel mutations (a small deletion c.2500delC, 4 non-sense mutations c.2182C>T, c.2630C>G, c.3677C>G, c.3189G>A; and 3 missense mutations; c.1273G>C, c.3679 G>C, and c.3992 T>C). Among these only 16 patients could be assigned FA-A complementation group, because we could not confirm single exon deletions detected by MLPA or cDNA amplification by secondary confirmation method and due to presence of heterozygous non-pathogenic variations or heterozygous pathogenic mutations. An effective molecular screening strategy should be developed for confirmation of these mutations and determining the breakpoints for single exon deletions.

DNA interstrand cross-link repair: understanding role of Fanconi anemia pathway and therapeutic implications.

Interstrand cross-links (ICLs) are extremely toxic DNA lesions that prevent DNA double-helix separation due to the irreversible covalent linkage binding of some agents on DNA strands. Agents that induce these ICLs are thus widely used as chemotherapeutic drugs but may also lead to tumor growth. Fanconi anemia (FA) is a rare genetic disorder that leads to ICL sensitivity. This review provides update on current understanding of the role of FA proteins in repairing ICLs at various stages of cell cycle. We also discuss link between DNA cross-link genotoxicity caused by aldehydes in FA pathway. Besides this, we summarize various ICL agents that act as drugs to treat different types of tumors and highlight strategies for modulating ICL sensitivity for therapeutic interventions that may be helpful in controlling cancer and life-threatening disease, FA.