[Diseases associated with lamin A/C gene defects: what the clinical cardiologist ought to know]

The nuclear lamina is a proteinaceous layer apposed to the inner nuclear membrane. It is composed of a family of polypeptides, the lamins, highly conserved in evolution. In mammals, 3 lamins, A, B and C have been described with molecular weights ranging from 60,000 to 78,000 Da. Lamins A and C have close sequence homology. Lamins can be classified with the intermediate filament polypeptides and consist of a central rod domain flanked by globular and carboxyl domains. Lamins are synthesized into the cytoplasm: lamins B and C are transported from the cytoplasm into the nucleus and their sequences are not cleaved but remain a permanent feature of the mature polypeptide. Vice versa, lamin A is not synthesized as a large precursor polypeptide. The lamin A/C gene (LMNA) is mapped to 1q21.2-q21.3. Lamins are expressed in a wide range of tissues, including adult heart and skeletal muscle. Naturally occurring mutations in LMNA have been shown to be responsible for distinct diseases called laminopathies, including dilated cardiomyopathy with or without conduction defect and with or without variable skeletal muscle involvement. In the cardiological setting, conduction defects associated with dilated cardiomyopathy are now a reliable marker for LMNA gene molecular screening.