Objective: To characterize the phenotypes of patients with juvenile and adult-onset acid maltase deficiency (AMD) in the French population and correlate them with genetic defects.
Background: AMD is an autosomal recessive disorder caused by the absence of the enzyme acid a-glucosidase (GAA). Patients are generally compound heterozygotes for various mutations in the GAA gene. The most common mutant allele is a -13T to G transversion in intron 1.
Methods: The authors performed a clinical, biochemical, and genetic study on 21 unrelated patients with juvenile and adult-onset AMD.
Results: Although onset of progressive muscle weakness occurred during adulthood in all cases but one, presence of mild, nonprogressive muscular symptoms appearing during childhood was detected in 16 patients. Eighteen patients had a similar clinical pattern with pelvic girdle muscle weakness predominating in glutei and thigh adductors. Restrictive respiratory insufficiency with vital capacity less than 60% was noted in eight patients, and respiratory failure was the first manifestation in two cases. All patients but one were compound heterozygotes, and 17 carried the IVS1 (-13T ---> G) transversion (one patient was homozygous for this mutation). The two mutated alleles were identified in 10 cases, with 13 different mutations detected in the GAA gene. There was no clear correlation between the type of mutation and phenotype.
Conclusions: This study shows a high genetic heterogeneity of juvenile and adult AMD in the French population. The absence of genotype-phenotype correlation suggests a complex physiopathology that requires further investigations.