Exome sequencing reveals a novel mutation, p.L325H, in the KRT5 gene associated with autosomal dominant Epidermolysis Bullosa Simplex Koebner type in a large family from western India

Genomics of rare genetic diseases-experiences from India

Home to a culturally heterogeneous population, India is also a melting pot of genetic diversity. The population architecture characterized by multiple endogamous groups with specific marriage patterns, including the widely prevalent practice of consanguinity, not only makes the Indian population distinct from rest of the world but also provides a unique advantage and niche to understand genetic diseases. Centuries of genetic isolation of population groups have amplified the founder effects, contributing to high prevalence of recessive alleles, which translates into genetic diseases, including rare genetic diseases in India.Rare genetic diseases are becoming a public health concern in India because a large population size of close to a billion people would essentially translate to a huge disease burden for even the rarest of the rare diseases. Genomics-based approaches have been demonstrated to accelerate the diagnosis of rare genetic diseases and reduce the socio-economic burden. The Genomics for Understanding Rare Diseases: India Alliance Network (GUaRDIAN) stands for providing genomic solutions for rare diseases in India. The consortium aims to establish a unique collaborative framework in health care planning, implementation, and delivery in the specific area of rare genetic diseases. It is a nation-wide collaborative research initiative catering to rare diseases across multiple cohorts, with over 240 clinician/scientist collaborators across 70 major medical/research centers. Within the GUaRDIAN framework, clinicians refer rare disease patients, generate whole genome or exome datasets followed by computational analysis of the data for identifying the causal pathogenic variations. The outcomes of GUaRDIAN are being translated as community services through a suitable platform providing low-cost diagnostic assays in India. In addition to GUaRDIAN, several genomic investigations for diseased and healthy population are being undertaken in the country to solve the rare disease dilemma.In summary, rare diseases contribute to a significant disease burden in India. Genomics-based solutions can enable accelerated diagnosis and management of rare diseases. We discuss how a collaborative research initiative such as GUaRDIAN can provide a nation-wide framework to cater to the rare disease community of India.

Application of whole exome sequencing in elucidating the phenotype and genotype spectrum of junctional epidermolysis bullosa: A preliminary experience of a tertiary care centre in India

BACKGROUND

Junctional epidermolysis bullosa (JEB) is a diverse group of genodermatoses associated with extreme skin fragility. Despite several well-characterized genetic studies, molecular diagnosis of this heterogeneous group is still challenging. Recent advances in the field of genomics have seen the successful implementation of whole exome sequencing (WES) as a fast and efficient diagnostic strategy in several genodermatoses.

OBJECTIVE

In view of the scarcity and need of molecular studies for JEB in India, we sought to explore the potential of WES in understanding the mutational spectrum of this rare, in certain subtypes lethal, sub-group of EB.

METHODS

WES was performed using genomic DNA from each case of EB, followed by massively parallel sequencing. Resulting reads were mapped to the human reference genome hg19. Sanger sequencing subsequently confirmed the potentially pathogenic mutations.

RESULTS

Overall, four unrelated families (6 patients) of JEB with a highly variable clinical presentation including a rare case of LOC syndrome were studied. WES revealed 4 variations in 3 genes (LAMA3, LAMB3 and COL17A1) that are implicated in JEB. None of the variations were recurrent. In addition we proposed the probable molecular consequence of a missense mutation on the structure-function relationship of lamininβ3 protein through computational modeling studies.

CONCLUSIONS

Being the first report documenting the phenotype-genotype correlations of JEB patients from India, our preliminary experience with WES is clearly encouraging and serves as a nidus for future large-scale molecular studies to actively identify and understand JEB patients in Indian population.

Case Report: Whole exome sequencing reveals a novel frameshift deletion mutation p.G2254fs in COL7A1 associated with autosomal recessive dystrophic epidermolysis bullosa

Dystrophic epidermolysis bullosa simplex (DEB) is a phenotypically diverse inherited skin fragility disorder. It is majorly manifested by appearance of epidermal bullae upon friction caused either by physical or environmental trauma. The phenotypic manifestations also include appearance of milia, scarring all over the body and nail dystrophy. DEB can be inherited in a recessive or dominant form and the recessive form of DEB (RDEB) is more severe. In the present study, we identify a novel p.G2254fs mutation in COL7A1 gene causing a sporadic case of RDEB by whole exome sequencing (WES). Apart from adding a novel frameshift Collagen VII mutation to the repertoire of known mutations reported in the disease, to the best of our knowledge, this is the first report of a genetically characterized case of DEB from India.

Case Report: Whole exome sequencing helps in accurate molecular diagnosis in siblings with a rare co-occurrence of paternally inherited 22q12 duplication and autosomal recessive non-syndromic ichthyosis

Lamellar ichthyosis (LI), considered an autosomal recessive monogenic genodermatosis, has an incidence of approximately 1 in 250,000. Usually associated with mutations in the transglutaminase gene ( TGM1), mutations in six other genes have, less frequently, been shown to be causative. Two siblings, born in a collodion membrane, presented with fish like scales all over the body. Karyotyping revealed duplication of the chromosome arm on 22q12+ in the father and two siblings. Whole exome sequencing revealed a homozygous p.Gly218Ser variation in TGM1; a variation reported earlier in an isolated Finnish population in association with autosomal recessive non-syndromic ichthyosis. This concurrence of a potentially benign 22q12+ duplication and LI, both rare individually, is reported here likely for the first time.