Schematic representation of SMA-related genes in MLPA assays. Gray, RAD17, SERF1B and GTF2H2, near the disease-determining gene. Arrows, relative position and 5′-to-3′ direction of SMA-related genes. Blank boxes, exons (E). Important MLPA probes are above related genes. *, probes complementary to common regions in exons 1, 4, 6, 8 of either SMN1 or SMN2; #, probes specific for SMN or NAIP genes.