Clinical improvement in a case of atypical infantile onset Pompe disease with enzyme replacement therapy

Targeted population screening of late onset Pompe disease in unspecified myopathy patients for Korean population

We performed targeted population screening of late onset Pompe disease (LOPD) in unspecified myopathy patients, because early diagnosis is difficult due to its heterogeneous clinical features. We prospectively enrolled 90 unrelated myopathic patients who had one or more signs out of five LOPD-like clinical findings (proximal weakness, axial weakness, lingual weakness, respiratory difficulty, idiopathic hyperCKemia). Acid alpha glucosidase activity was evaluated with dried blood spot and mixed leukocyte simultaneously. For a final diagnosis of LOPD, 16 patients with decreased enzyme activity were genotyped by GAA molecular analysis. We found two patients with LOPD (2.2%), and the remaining 14 patients had at least one G576S or E689K mutation, known as the pseudodeficiency allele. Acid alpha glucosidase activity of LOPD patients was significantly lower than that of patients with at least one pseudodeficiency allele (p = 0.017). This study is the first LOPD screening study for targeted Korean population, and more generally, an Asian population. Our findings suggest that for diagnosis of LOPD in Asian population, modified cutoff value of acid alpha glucosidase activity with dry blood spot considering that of patients having heterozygote pathogenic variants or pseudodeficiency alleles may reduce time and cost requirements and increase the comfort of patients.

Hypertrophic cardiomyopathy in pompe disease is not limited to the classic infantile-onset phenotype

Pompe disease is a genetic disorder caused by a deficiency of acid α-glucosidase (GAA). Patients with classic infantile-onset Pompe disease usually present with hypertrophic cardiomyopathy and die before 1 year of age, if not treated with enzyme replacement therapy (ERT). In comparison, patients with late-onset Pompe disease typically do not have hypertrophic cardiomyopathy. However, here we describe five patients who presented with hypertrophic cardiomyopathy but did not fit the criteria of classic infantile-onset Pompe disease. Their ages at diagnosis of cardiomyopathy were 1 month in two patients following detection of an audible cardiac murmur and 2-3 years in the three remaining patients. All patients survived for 5-8 years without ERT. Three patients died before the advent of ERT from causes other than congestive heart failure. One patient had a good response to ERT starting at 5 years of age. The sibling of one patient, who did not receive ERT and died at age seven, was diagnosed prenatally. At 3 months of age, the sibling had hypertrophic cardiomyopathy, and a muscle biopsy at that time revealed glycogen accumulation.This case series demonstrates that Pompe disease is a continuum of disease, and the development of cardiomyopathy is not limited to classic infantile-onset Pompe disease. These patients do not fit into the discrete phenotypes of infantile- or late-onset Pompe disease, which may suggest reconsidering the nomenclature of Pompe disease.