Genotype-phenotype analysis in X-linked Emery-Dreifuss muscular dystrophy and identification of a missense mutation associated with a milder phenotype.

Direct sequencing of the emerin gene in 22 families with Emery-Dreifuss muscular dystrophy (EMD) revealed mutations in 21 (95%), confirming that emerin mutations can be identified in the majority of families with X-linked EMD. Most emerin mutations result in absence of the protein. In this study three mutations (a missense mutation Pro183Thr and two in-frame deletions removing residues 95-99 and 236-241, respectively) were unusual in being associated with expression of mutant protein. The phenotype in these families was compared in detail with the clinical features in cases with typical null mutations. For the in-frame deletions there were no significant differences. In the family with the missense mutation the phenotype was milder. Age at onset was later for first symptoms and for development of ankle contractures and muscle weakness. These findings have diagnostic implications as well as pointing to functionally important regions of the emerin protein.

Identification of new mutations in the Emery-Dreifuss muscular dystrophy gene and evidence for genetic heterogeneity of the disease.

The Emery-Dreifuss Muscular Dystrophy (EDMD) is an X-linked recessive muscular disorder characterized by early contractures of the elbows, Achilles tendons and postcervical muscles, slowly progressing muscle wasting and weakness and a cardiomyopathy characterized by conduction defects. Heart block is a frequent cause of death. Finding of mutations in one of the transcripts in the critical region in distal Xq28 led to the identification of the gene responsible for the disease. We now report the sequence of the gene which is 2100 bp long and the development of a set of primers to amplify and sequence the gene from patients' DNA. Eight unrelated X-linked familial cases were studied and they all carried different mutations, showing that lack of emerin in cardiac and skeletal muscle is the cause of the X-linked disease. No mutations were found in a family where the female carrier was affected nor in a sporadic case with a well established diagnosis of EDMD. Our findings suggest genetic heterogeneity of EDMD, and that at least two genes, the X-linked STA gene and one unidentified autosomal gene, are responsible for the disease.