Glycogenosis type II: A juvenile-specific mutation with an unusual splicing pattern and a shared mutation in African Americans

The recessively inherited deficiency of acid α-glucosidase (GAA) called Glycogenosis Type II is expressed as three different phenotypes: infantile, juvenile, and adult. At the molecular level, infantile and adult forms of the disease have been extensively studied, but little is known regarding the genetic defects associated with the juvenile form. We describe a novel mutation that defines the intermediate juvenile phenotype in a compound heterozygous patient. A transversion of t to g in intron 6 at position -22 creates a cryptic acceptor site and results in unusual splicing abnormality: insertion of 21 nucleotides of the intronic sequence into mRNA and removal of exon 6 without disruption of the reading frame. The second mutation, Arg854Stop in exon 18, had been previously identified in another African- American patient (Hermans et al., 1993a). Family study indicates that a silent allele harboring the Arg854Stop mutation in our patient is inherited from the patient's father, who is also African American, thus suggesting a common mutation in this population.