Clinical and Genetic Characterization of Hereditary Epidermolysis Bullosa and Ichthyoses in Three Consanguineous Families

Abstract

The skin makes a barrier between the organism and its surrounding environment and plays a protective role along with the distinctive functions of lubrication and thermoregulation. The skin appendages, including nails, teeth, sweat glands, and hairs share common functions like immune surveillance, epidermal barrier, and role in pigmentation and defense mechanism in the skin. Genetic defects in the genes involved in the development of skin or associated appendages lead to inherited skin disorders collectively known as ectodermal dysplasia. Epidermolysis Bullosa and Ichthyosis are two inherited skin disorders. Epidermolysis Bullosa is a hereditary skin disorder described by skin blister formations upon minor injury or mechanical traumas. On the other hand, ichthyosis is characterized by dry skin, scaling, and hyperkeratosis of the skin surface. It has syndromic as well as non-syndromic forms. The molecular basis of these manifestations being understood by the identification of variants in genes involved in skin barrier formation. The current study in the thesis investigated the three consanguineous Pakistani families (A C), segregating various types of autosomal recessive congenital skin disorders at clinical and genetic level. Family A presented Epidermolysis Bullosa, family B showed lamellar ichthyosis, and family C had the autosomal recessive type of ichthyosis phenotypes. Genotyping using microsatellite markers closely located to the previously ectodermal dysplasia-associated loci and haplotype analysis were used to establish linkage in these families. Sanger sequencing followed by in silico analysis were used to identify causative variants of the disease phenotypes. Family A was found linked to the EXPH5 gene located on chromosome 11q22.3 whereas, family B revealed linkage to the CERS3 gene located on chromosome 15q26.3. Family C affected individuals were found heterozygous for various combinations of parental alleles thus, excluding family C from linkage to ten previously reported causative genes. Sanger sequencing of coding regions and exon-intron borders of EXPH5 and CERS3 was performed by dideoxy chain termination method in families A, and B. In family A, all six DRSML QAU Abstract Clinical and Genetic Characterization of Hereditary Epidermolysis Bullosa and Ichthyoses in Three Consanguineous Families XII coding exons of the EXPH5 gene were sequenced which revealed no pathogenic variant, suggesting that the variation might be exist in regulatory sequences of the EXPH5 gene. In family B, Sanger sequencing data analysis depicted a novel splice site variant (c.466- 1G>A) in exon eight of CERS3 gene. The variant was found homozygous in the affected members, while heterozygous in phenotypically normal parents. Different prediction tools and ACMG classification predicted the variant likely pathogenic. In conclusion, the present study identified a novel variant only in one of the three families. The finding will be helpful in prenatal screening, carrier testing, genetic counseling of the affected and other families in the Pakistani population. Moreover, the study will bring awareness among Pakistani population to prevent genetic disorders by minimizing cousin marriages where a positive family history for any inherited disorders is present. In searching for disease-causing variants in family A and C, it is recommended to use whole genome/exome sequencing to find the causative genes