Manfred Wehnert

Mutations of the FHL1 Gene Cause Emery-Dreifuss Muscular Dystrophy

Emery-Dreifuss muscular dystrophy (EDMD) is a rare disorder characterized by early joint contractures, muscular dystrophy, and cardiac involvement with conduction defects and arrhythmias. So far, only 35% of EDMD cases are genetically elucidated and associated with EMD or LMNA gene mutations, suggesting the existence of additional major genes. By whole-genome scan, we identified linkage to the Xq26.3 locus containing the FHL1 gene in three informative families belonging to our EMD- and LMNA-negative cohort. Analysis of the FHL1 gene identified seven mutations, in the distal exons of FHL1 in these families, three additional families, and one isolated case, which differently affect the three FHL1 protein isoforms: two missense mutations affecting highly conserved cysteines, one abolishing the termination codon, and four out-of-frame insertions or deletions. The predominant phenotype was characterized by myopathy with scapulo-peroneal and/or axial distribution, as well as joint contractures, and associated with a peculiar cardiac disease characterized by conduction defects, arrhythmias, and hypertrophic cardiomyopathy in all index cases of the seven families. Heterozygous female carriers were either asymptomatic or had cardiac disease and/or mild myopathy. Interestingly, four of the FHL1-mutated male relatives had isolated cardiac disease, and an overt hypertrophic cardiomyopathy was present in two. Expression and functional studies demonstrated that the FHL1 proteins were severely reduced in all tested patients and that this was associated with a severe delay in myotube formation in the two patients for whom myoblasts were available. In conclusion, FHL1 should be considered as a gene associated with the X-linked EDMD phenotype, as well as with hypertrophic cardiomyopathy.

Identification, mapping, and genomic structure of a novel X-chromosomal human gene (SMPX) encoding a small muscular protein

Abstract. Reciprocal probing has been used to identify a cDNA clone (xh8H11) representing a gene preferentially expressed in striated muscle. The gene maps close to DXS7101 31.9xa0cM from the short arm telomere of the X-chromosome at Xp22.1. On searching expressed and genomic databases, 21 expressed sequence tags were found that allowed the assignment of a human extended consensus sequence of 887xa0bp, suggesting a completely expressed gene symbolized as SMPX. By using the human consensus sequence, the orthologous mouse Smpx and rat SMPX genes could be aligned and confirmed by complete sequencing of additional SMPX-related clones obtained by library screening. An open reading frame was identified encoding a peptide of 88–86 and 85 amino acids in human and rodents, respectively. The predicted peptide had no significant homologies to known structural elements. The human consensus cDNA sequence was used to define the genomic structure of the human SMPX that had been missed by a previous large scale sequencing approach. The gene consists of five exons (≥172, 57, 84, 148, ≥422xa0bp) and four introns (3639, 10410, 6052, 31134xa0bp) comprising together 52.1xa0kb and is preferentially and abundantly expressed in heart and skeletal muscle. Thus, a novel human gene encoding a small muscular protein that maps to Xp22.1 (SMPX) has been identified and structurally characterized as a basis for further functional analysis.

The retinol acid receptor B gene is hypermethylated in patients with familial partial lipodystrophy.

Mutations in the LMNA gene cause various phenotypes including partial lipodystrophy, muscular dystrophies, and progeroid syndromes. The specific mutation position within the LMNA sequence can partially predict the phenotype, but the underlying mechanisms for the development of these different phenotypes are still unclear. To investigate whether different DNA methylation patterns contribute to the development of different phenotypes caused by LMNA mutations, we analyzed a panel of ten candidate genes related to fat metabolism, aging, and a tendency to different methylation patterns: CSPG2, ESR1, IGF1R, IGFR2, LMNA, MLH1, RANBP1, RARB, ZMPSTE24, and TGFBR1. We studied two independent families each comprising three individuals affected by familial partial lipodistrophy type 2 (FPLD2). Affected members in each family carried two different mutations of the LMNA gene (R482L and R471G respectively). In addition, we analyzed four progeria patients (2xLMNA/C G608G, 1xLMNA/C S143F, and 1xZMPSTE24 IVS9-Ex10) and seven healthy adults. The gene encoding retinoic acid receptor B (RARB) showed a higher methylation in all six patients with FPLD2 when compared with the progeria patients with other LMNA mutations as well as the healthy controls (P<0.05). All other investigated genes showed no difference in the methylation patterns between the groups. A drug-induced inhibition of the retinol pathway is discussed as the key pathway for developing HAART-associated lipodystrophy and our data support a possible role of the retinol pathway in the development of lipodystrophy phenotypes.