SMN2 and proximal spinal muscular atrophy: Table 3 provides an overview of the SMN2 copy number as determined by MLPA. After completion of all validation experiments, SMN2 copy numbers of SMA patients were compared with the SMN2 copy numbers previously determined in peripheral blood for diagnostic purposes by the University Medical Centre Utrecht (UMCU). For 3 out of 43 SMA patients, a different SMN2 copy number was found between the UMCU results and the present validation study. For four out of 47 SMA patients, no SMN2 data were available at the UMCU.