[The contribution of molecular genetics to the study of spinal muscular atrophy]

Spinal muscular atrophies constitute a group of hereditary diseases characterized by degeneration of the anterior horn of the spinal cord. Molecular studies began in 1990 with the location of the genome region responsible for the disease in chromosome 5q13. New directions for research were opened in 1995 with the identification of the affected region in the survival motor neuron (SMN) genes and the neuronal apoptosis inhibitory protein genes. A main feature of these genes is that they are duplicate, forming part of two elements (centromeric and telomeric) that include mini-satellites that are also repeated, making this zone particularly unstable. The molecular abnormalities found in patients are a consequence of that instability: gene deletions and conversions in the SMN gene have been described independently of whether symptoms were severe or not. Molecular data make it possible to confirm the clinical diagnosis of most patients and to provide certain prenatal diagnosis for couples that are at high risk of passing on the disorder. Determining both the function of these genes and their pathogenesic role will help to ground new therapeutic strategies that will prevent or detain motor neuron degeneration.