Résumé :
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Proximal spinal muscular atrophy (SMA) are a group of motor neuropathies characterized by the degeneration of spinal montoneurons leading to muscular paralysis with muscular atrophy. They are the second most fatal autosomal recessive disease, with an incidence of approximately 1 in 10,000. Childhood SMA is divided into three types (I to III) according to age of onset and severity of the disease, while type IV concerns adult-onset SMA. SMA is caused by mutations in the survival motor neuron 1 (SMN1) gene, with more than 90% of patients having a homozygous deletion of exon 7 in this gene. The aim of this work was to explore Algerian patients for whom a clinical diagnosis of spinal muscular atrophy has been suspected. 300 patients have been tested by PCR-based methods, all for the detection of the homozygous deletion of exon 7 of SMN1, while some of them have been investigated for the presence of gene conversion events affecting exons 7 and 8 of this gene. Molecular results showed that about 70% of the patients had the homozygous deletion of exon 7 of SMN1, thus establishing a precise genetic diagnosis for these patients. All the SMA patients clinically suspected type I had this deleterious mutation, while those of type II and III displayed it in approximately 50-60% of the cases. For type IV, we could detect this mutation in only 10% of the patients. The search for gene conversion events affecting exons 7 and 8 of SMN1 allowed us to identify 3% patients with this molecular alteration. The relative low frequency of SMN1 exon 7 homozygously deleted patients suggests that other types of mutations could affect this gene, or that other genes could be involved in the non-deleted patients, or more probably that clinical diagnosis of SMA could be overestimated by the clinicians.
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