• Identification and Computational Analysis of Novel Pathogenic Variants in Pakistani Families with Diverse Epidermolysis Bullosa Phenotypes

      Khan, Fehmida F; Khan, Naima; Rehman, Sakina; Ejaz, Amir; Ali, Uzma; Erfan, Muhammad; Ahmed, Zubair M; Naeem, Muhammad (MDPI AG, 2021-04-22)
      Epidermolysis bullosa (EB) includes a group of rare gesnodermatoses that result in blistering and erosions of the skin and mucous membranes. Genetically, pathogenic variants in around 20 genes are known to alter the structural and functional integrity of intraepidermal adhesion and dermo-epidermal anchorage, leading to four different types of EB. Here we report the underlying genetic causes of EB phenotypes segregating in seven large consanguineous families, recruited from different regions of Pakistan. Whole exome sequencing, followed by segregation analysis of candidate variants through Sanger sequencing, identified eight pathogenic variants, including three novel (ITGB4: c.1285G>T, and c.3373G>A; PLEC: c.1828A>G) and five previously reported variants (COL7A1: c.6209G>A, and c.1573C>T; FERMT1: c.676insC; LAMA3: c.151insG; LAMB3: c.1705C>T). All identified variants were either absent or had very low frequencies in the control databases. Our in-silico analyses and 3-dimensional (3D) molecular modeling support the deleterious impact of these variants on the encoded proteins. Intriguingly, we report the first case of a recessively inherited form of rare EBS-Ogna associated with a homozygous variant in the PLEC gene. Our study highlights the clinical and genetic diversity of EB in the Pakistani population and expands the mutation spectrum of EB; it could also be useful for prenatal diagnosis and genetic counseling of the affected families.
    • Identification of Frameshift Variants in Gene Causing Xeroderma Pigmentosum in Two Consanguineous Pakistani Families.

      Zamani, Ghazala Y; Khan, Ranjha; Karim, Noreen; Ahmed, Zubair M; Naeem, Muhammad (MDPI AG, 2022-03-19)
      Xeroderma pigmentosum (XP) is a rare autosomal recessive genetic disorder characterized by severe sensitivity of skin to sunlight and an increased risk of skin cancer. XP variant (XPV), a milder subtype, is caused by variants in the POLH gene. POLH encodes an error-prone DNA-polymerase eta (pol eta) which performs translesion synthesis past ultraviolet photoproducts. The current study documents the clinical and genetic investigations of two large consanguineous Pakistani families affected with XPV. In family 1, whole exome sequencing (WES) revealed a novel frameshift variant, c.1723dupG (p.(Val575Glyfs*4)), of POLH, which is predicted to cause frameshift and premature truncation of the encoded enzyme. Indeed, our ex vivo studies in HEK293T cells confirmed the truncation of the encoded protein due to the c.1723dupG variant. In family 2, Sanger sequencing of POLH exons, revealed a recurrent nonsense variant, c.437dupA (p.Tyr146*). POLH forms a hetero-tetrameric POLZ complex with REV3L, REV7, POLD2 and POLD3. Next, we performed in silico analysis of POLH and other POLZ complex genes expression in publicly available single cell mRNAseq datasets from adult human healthy and aging skin. We found overlapping expression of POLH, REV3L and POLD2 in multiple cell types including differentiated and undifferentiated keratinocytes, pericytes and melanocytes in healthy skin. However, in aging human skin, POLH expression is reduced in compare to its POLZ complex partners. Insights from our study will facilitate counseling regarding the molecular and phenotypic landscape of POLH-related XPV.