MLPA assay for the molecular diagnosis of SMA is based on a kit containing several probes for the SMA critical region, including specific probes for SMN1 and SMN2 genes, probes able to hybridize both genes and other probes for sequences mapped either within the SMA critical region (NAIP, GTF2H2, N-cadherin-like, CDH6 and RAD17 genes) or on other autosomal regions. The gene discussed is SMN2; the disease is proximal spinal muscular atrophy.