Genetic and molecular analyses of Turkish patients with pelizaeus - merzbacher disease

Abstract

Pelizaeus-Merzbacher disease (PMD) is a rare inherited leukodystrophy with Xlinked recessive segregation. About 80 per cent of patients with PMD have been associated with mutations of the PLP1 gene on Xq21.3-Xq22 which encodes two proteins, PLP1 and DM20, expressed abundantly in oligodendrocytes. Mutations of GJA12 gene on 1q41-42 are responsible for some of the PMD cases with autosomal recessive inheritance. In the framework of this study, the molecular basis of PMD was investigated in a cohort of 21 Turkish families with PMD. In total, pathogenic mutations were identified in 57 per cent of the families, 19 per cent of which were due to PLP1 duplications, and nine and 29 per cent were due to mutations in the PLP1 and GJA12 genes, respectively. The distribution of the mutations identified in our cohort of patients was different from those reported in the literature, which may result due to the high frequency of consanguinity and autosomal recessive cases in our population. Absence of mutations in PLP1 or GJA12 genes in 43 per cent of the cases analyzed suggests presence of further genetic heterogeneity in PMD. In vitro immunocytochemical analyses of two PLP1 mutations identified in our cohort revealed that accumulation of mutant proteins in the endoplasmic reticulum, leading to UPR activation and subsequent apoptosis were observed for the mutant proteins. However, one of the mutations showed a different pattern of localization for DM20 isoform. Since patients present similar clinical features, the results implicate that PLP1 and DM20 may have different roles in myelin.|Keywords: Pelizaeus-Merzbacher Disease, Dysmyelination, Proteolipid Protein 1 (PLP1) Gene, Gap Junction Protein Alpha12 (GJA12) Gene, Unfolded Protein Response (UPR)