The loci for the diseases for which GLBs have been reported are as follows: Werdnig-Hoffman disease, survival motor neuron 1 (SMN1) on 5q13.2; Krabbe disease, galactocerebrosidase (GALC) on 14q31.3; and 13q deletion syndrome, [46, XY, del (13) (q22q31)]. The gene discussed is SMN1; the disease is spinal muscular atrophy, type 1.