Otozomal Resesif Limb-Girdle Kas Distrofisi Tanısı Alan Ailelerde Yeni Gen Araştırılması

Abstract

Limb-girdle muscular dystrophies (LGMD) are a clinically and genetically heterogeneous group of hereditary muscle disorders characterized by symmetric, proximal and progressive muscular weakness. In this thesis, four consanguineous families diagnosed with autosomal recessive LGMD (LGMD2) which are not linked to any of the known LGMD2 loci were studied. The aim of this thesis was to identify the chromosomal localization of a novel mutant gene responsible for LGMD2 by performing genome-wide homozygosity mapping using 250K NspI SNP array data. In one family, the disease was mapped to a homozygous haplotype in chromosomal region 1q25. DNA sequencing of TOR1AIP1 encoding LAP1B (lamina-associated polypeptide 1B) in this critical chromosomal region showed a homozygous c.186delG mutation (p.E62fsTer25) in the three affected individuals. Relative quantitation of TOR1AIP1 mRNA by quantitative real-time PCR showed that the level of expression in the skeletal muscle of the patient was 5,88-fold lower than in the control sample. Western blot and immunofluorescent staining demonstrated that LAP1B was absent in the patient's skeletal muscle fibres. Ultrastructural examination showed alterations of the nuclear envelope including nuclear fragmentation and altered chromatin condensation. LAP1B is an integral protein of the inner nuclear membrane that binds to both A-type and B-type lamins, and is involved in the regulation of torsin A ATPase. This thesis expands the spectrum of genes associated with nuclear envelopathies and underlies a critical role for LAP1B in striated muscle.