The earliest enzyme replacement for infantile‐onset Pompe disease in Japan

Background Infantile‐onset Pompe disease (IOPD) is the most severe phenotype of a lysosomal storage disorder caused by acid alpha‐glucosidase (GAA) deficiency. An enzymatic newborn screening (NBS) program started regionally in Japan in 2013 for early enzyme replacement therapy (ERT). We report the ERT responses of the first NBS‐identified Japanese IOPD case and of another case diagnosed prior to NBS, to discuss the problems of promptly starting ERT in Japan. Methods Acid alpha‐glucosidase activity was measured by fluorometric assay in both patients. The diagnosis of IOPD was confirmed by next‐generation followed by Sanger‐method sequencing (patient 1) or direct sequencing of polymerase chain reaction (PCR)‐amplified products (patient 2) of the GAA gene. Results A female infant identified by NBS had a novel out‐of‐frame (p.F181Dfs*6) variant and a reported pathogenic (p.R600C) variant, along with two pseudodeficiency variants. Enzyme replacement therapy was started at age 58 days when the infant had increased serum levels of creatine kinase and slight myocardial hypertrophy. Clinical and biochemical markers improved promptly. She has been alive and well without delayed development at age 14 months. Patient 2, a Japanese male, received a diagnosis of IOPD at age 5 months before the NBS era. He had a homozygotic variant of GAA (p.R608X), later registered as a cross‐reactive immunological material (CRIM)‐negative genotype, and developed a high titer of anti‐rhGAA antibodies. The patient has survived myocardial hypertrophy with continuous respiratory support for 12 years of ERT. Conclusions Enzyme replacement therapy should not be delayed over the age of 2 months for reversible cardiac function, although CRIM‐negative cases may hamper turnaround time reduction.