A novel role for CSRP1 in a Lebanese family with both cardiac defects and polydactyly -

Abstract

Abnormal cardiac development leads to human congenital heart disease (CHD), which is responsible for the vast majority of neonates’ death around the world. Although the major cause is still unknown, CHD has several etiologies ranging from genetic variations, environmental factors in addition to other factors. CHD affect various parts of the heart and it is classified into different broad categories including defects in the septa of atria and ventricles. In this thesis, we describe a Lebanese family composed from the consanguineous marriage between two first-degree cousins. Out of seven conceived children, two died in utero at the ages of 6 and 9 months of unknown causes. Of the remaining five children, three have congenital heart disease (ventricular septal defect, atrial septal defect, and patent ductus arteriosus), and four have polydactyly. Targeted exome sequencing of 119 genes, identified a heterozygote duplication of a 14 nucleotide fragment in exon 5 of CSRP1, causing a frameshift mutation at position 154 of the protein. Genotyping all family members with Sanger sequencing showed that this mutation is segregating with the CHD phenotype but not with polydactyly except for the father who has no cardiac problems and yet is positive for the mutation. The variant was not found in 200 exomes of Lebanese origin neither in the gnomAD. CSRP1 encodes a LIM domain protein, shown to be implicated in smooth muscle function. Our in silico analysis revealed that p.E154Vfs*99 mutation totally disrupts the second LIM domain. Thus, we hypothesized that this mutation is deleterious and is the cause of the cardiac defects in the family. First of all, we showed by immunohistochemistry a strong expression of the protein in the heart of mouse embryos at all stages of development starting as early as E12.5 and onwards with a strong nuclear expression in all cardiac compartments, but not in the valves. After generating the MUT CSRP1, immune-staining done on Hela cells shows that p.E154Vfs*99 mutation does not affect the ce