Sequence Analysis of Candidate Genes Involved in Causing Bone Deformities in Consanguineous Families

Abstract

Polydactyly is a genetic limb disorder characterized by the presence of an extra digit. Postaxial polydactyly (PAP) refers to one or more additional digits at the ulnar or fibular side of the hand or foot respectively. Syndactyly stands out as one of the most diverse developmental deformities documented in medical literature. Various combinations exist where adjacent fingers or toes remain connected by a web, allowing for unilateral or bilateral occurrences, as well as symmetrical or asymmetrical manifestations. The study presented in this dissertation was aimed to hunt down the disease-causing genes and mutations involved in the pathogenesis of distinctive skeletal disorders in four families (A, B). Family A showing an autosomal recessive or X-linked recessive inheritance pattern in the consanguineous family was followed for WES. Clinical features observed in affected individuals of family A included Postaxial polydactyly type A. The WES followed by Sanger sequencing was performed to identify the potential disease causing variant. Two variants of two genes located on X chromosome (WDR13 Xp11.23 exon2:c.C29T and MED12 Xq13.1 exon41:c.G5873C) and one variant of a gene (MEOX2 7P21.2 Exon1:c .225_230del) located on the autosomal chromosome were shortlisted. Sanger sequencing data does not show any pathogenic variant in these genes However, one affected member of the family showed a pathogenic variant and DNA Sanger sequencing of parents and other normal siblings will be further investigated to confirm segregation. In family B, clinical features observed in the patients included cutaneous syndactyly in the 4th and 5th toes with no other symptoms showing isolated syndactyly. Homozygosity mapping was tested for previously reported genes LRP4 (11p11.2), BHLHA9 (17p13.3), LMBR1 (7q36.3), CKAP2L (2q14.1), CHST1 (11p11.2), SMO (7q32.1), LAMA2 (6q22.33), SOST (17q21.31), PAX3 (2q36.1), EDNRB (13q22.3) and RAB23 (6p12.1-p11.2). None of the listed genes showed any linkage. However, one STS marker of HOXD12 (2q31.1) showed linkage. One exon of HOXD12 was sequenced which did not show any pathogenic variant so, the remaining exons will be sequenced. If no pathogenic variant is found, then family B will be subjected to whole exome sequencing and there might be a novel gene involved in causing disease in this family