The infantile form of GSD II (an inherited deficiency of the lysosomal enzyme, acid alpha-glucosidase, Pompe disease) is a severe and invariably fatal disease characterized by a rapidly progressive generalized hypotonia, hepatomegaly, and cardiomegaly. We have recently demonstrated that African American patients share a common nonsense R854X mutation in exon 18 (Becker et al., 1998). Two other mutations, D645E and M519V, have been identified in individual African American patients (Hermans et al., 1993a; Huie et al., 1994a). We describe here three novel mutations in this population group: a missense W481R in exon 10, a deletion of a T1441 in exon 10, and a splicing defect at the 5' donor site of intron 8 (IVS g+la) . The splicing defect is shared by two unrelated patients and it is linked to intragenic polymorphic sites identical to those found in patients bearing the common R854X mutation.