The spinal muscular atrophies are a group of disease characterized by loss or degeneration of the neurons of the horn previous of the spinal marrow. The bad operation of the same ones makes that the nervous impulse cannot be transmitted correctly so that the movements like the muscular tone are affected. The SMA is classified in five groups: SMA proximal, variants of the childhood, non proximal, paralysis bulbar and espinobulbar Kennedy type. In turn, the Infantile Spinal Muscular Atrophy (SMAi) that is a variant of the childhood, it is classified in three groups in dependence of the appearance age and clinical severity. One of the genes responsible for this disease is known as gene of the survival of the neuron (SMN), it is located in the chromosome 5 (5q 11.2 – 13.3), it presents two copies one in the region telomérica (SMN t or SMN1) of the chromosome and another in the centromérica (SMNc or SMN2) and it codes to the protein Smn. Until the moment a good therapy is not known for this illness, so that the molecular diagnosis is of great importance to improve the quality of life of the affected families.

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