Laminopathies have emerged as clinically heterogeneous genetic disorders due to mutations in lamins or lamin-associated proteins. Lamins are structural protein components of the nuclear lamina, a protein network underlying the inner nuclear membrane that determines nuclear shape and size. The lamins constitute a class of intermediate filaments. Three types of lamins, A, B, and C, have been described in mammalian cells.
Laminopathies regroup at least eight distinct diseases, belonging to the groups of skeletal and/or cardiac muscular dystrophies, axonal neuropathies, premature ageing syndromes and familial lipodystrophies. These diseases, such as Emery-Dreifuss muscular dystrophy, Hutchinson-Gilford progeria syndrome and limb-girdle muscular dystrophy type 1B (LGMD1B), result from alterations in the LMNA gene, encoding type A-lamins.
Pathophysiological mechanisms explaining how mutations in a unique gene could lead to such various phenotypes are still unknown, but probably involve alterations in cellular mechanical stress responses, in gene expression, and/or in post-translational maturation of lamin A. One gene that is involved in the post-translational processing of Lamin A precursor is ZMPSTE24 (also known as FACE-1 in human). Loss of function of the ZMPSTE24 gene and accumulation of precursor lamin A has been correlated with restrictive dermopathy (RD).
Mutations in the MYOT gene are associated with LGMD1A and myofibrillar myopathies. Mutations in the CAV3 gene are associated with LGMD1C.
The LMNA gene (12 exons) spans ~25.4 kb of genomic DNA and is located on 1q22, ~154 Mb from the p-telomere. The ZMPSTE24 gene (10 exons) spans ~36.1 kb of genomic DNA and is located on 1p34.2, ~40.5 Mb from the p-telomere. The MYOT gene (10 exons) spans ~20 kb of genomic DNA and is located on chromosome 5q31.2, ~137.2 Mb from the p-telomere. The CAV3 gene (2 exons) spans ~13 kb of genomic DNA and is located on chromosome 3p25.3, ~8.8 Mb from the p-telomere.
The P048-C2 probemix contains probes for all 12 exons of the LMNA gene. Two probes are present for exon 1. This probemix furthermore contains probes for all exons of the ZMPSTE24, MYOT and CAV3 genes. Finally, 9 reference probes are included in this probemix, detecting several different autosomal chromosomal locations.
This SALSA® MLPA® probemix is designed to detect deletions/duplications of one or more sequences in the aforementioned genes in a DNA sample. Heterozygous deletions of recognition sequences should give a 35-50% reduced relative peak height of the amplification product of that probe. Note that a mutation or polymorphism in the sequence detected by a probe can also cause a reduction in relative peak height, even when not located exactly on the ligation site! In addition, some probe signals are more sensitive to sample purity and small changes in experimental conditions. Therefore, deletions and duplications detected by MLPA should always be confirmed by other methods. Not all deletions and duplications detected by MLPA will be pathogenic; users should always verify the latest scientific literature when interpreting their findings. We have no information on what percentage of defects in these genes is caused by deletions/duplications of complete exons. Finally, note that most defects in this gene are expected to be small (point) mutations which will not be detected by this SALSA® MLPA® test.