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Abstract: Systematic correlation of phenotype with genotype is a key goal of the emerging field of phenomics, which is expected to help define complex diseases. Careful evaluation of phenotype–genotype associations in monogenic disorders, such as laminopathies, might provide new hypotheses to be tested with molecular and cellular studies and might also suggest potential new intervention strategies. For instance, evaluation of the clinical features of carriers of mutant LMNA in kindreds with familial partial lipodystrophy suggests rational, staged intervention using established pharmaceutical agents to prevent cardiovascular complications not just for patients with lipodystrophy but by extension for patients with the common metabolic syndrome. Careful non-invasive imaging shows phenotypic differences between partial lipodystrophy due to mutant LMNA and not due to mutant LMNA. Furthermore, hierarchical cluster analysis detects systematic relationships between organ involvement in laminopathies and mutation position in the LMNA genomic sequence. However, sometimes the same LMNA mutation can underlie markedly different clinical phenotypes; cellular and molecular experiments can help to explain the mechanistic basis for such differences. Finally, promising novel treatment modalities for laminopathies, such as farnesyl transferase inhibition and gene-based therapies, might help not only to illuminate mechanisms that link genotype to phenotype, but also to provide hope for patients suffering with laminopathies, since these treatments are designed to modulate key early or proximal steps in the pathogenesis of these disorders. [Copyright &y& Elsevier]

Abstract: LMNA mutations are responsible for a variety of genetic disorders, including muscular dystrophy, lipodystrophy, and certain progeroid syndromes, notably Hutchinson-Gilford Progeria. Although a number of clinical features of these disorders are suggestive of accelerated aging, it is not known whether cells derived from these patients exhibit cellular phenotypes associated with accelerated aging. We examined a series of isogenic skin fibroblast lines transfected with LMNA constructs bearing known pathogenic point mutations or deletion mutations found in progeroid syndromes. Fibroblasts overexpressing mutant lamin A exhibited accelerated rates of loss of telomeres and shortened replicative lifespans, in addition to abnormal nuclear morphology. To our surprise, these abnormalities were also observed in lines overexpressing wild-type lamin A. Copy number variants are common in human populations; those involving LMNA, whether arising meiotically or mitotically, might lead to progeroid phenotypes. In an initial pilot study of 23 progeroid cases without detectable WRN or LMNA mutations, however, no cases of altered LMNA copy number were detected. Nevertheless, our findings raise a hypothesis that changes in lamina organization may cause accelerated telomere attrition, with different kinetics for overexpession of wild-type and mutant lamin A, which leads to rapid replicative senescence and progroid phenotypes. [Copyright &y& Elsevier]

Abstract: Laminopathies are a group of genetic disorders caused by LMNA mutations; they include muscular dystrophies, lipodystrophies, and progeroid syndromes. We identified a novel heterozygous LMNA mutation, L59R, in a patient with the general appearance of mandibuloacral dysplasia and progeroid features. Examination of the nuclei of dermal fibroblasts revealed the irregular morphology characteristic of LMNA mutant cells. The nuclear morphological abnormalities of LMNA mutant lymphoblastoid cell lines were less prominent compared to those of primary fibroblasts. Since it has been reported that progeroid features are associated with increased extracellular matrix in dermal tissues, we compared a subset of these components in fibroblast cultures from LMNA mutants with those of control fibroblasts. There was no evidence of intracellular accumulation or altered mobility of collagen chains, or altered conversion of procollagen to collagen, suggesting that skin fibroblast-mediated matrix production may not play a significant role in the pathogenesis of this particular laminopathy. [Copyright &y& Elsevier]