Prenatal diagnosis of Pompe disease by electron microscopy

Pompe disease: literature review and case series

Pompe disease is a rare multi-systemic metabolic myopathy caused by autosomal recessive mutations in the acidic alpha glucosidase (GAA) gene. Significant progress had been made in the diagnosis and management of patients with Pompe disease. Here, we describe our experience with 12 patients with various forms of Pompe disease including 4 potentially pathogenic, novel GAA variants. We also review the recent the recent advances in the pathogenesis, diagnosis, and treatment of individuals with Pompe disease.

Skeletal muscle pathology of infantile Pompe disease during long-term enzyme replacement therapy

Background

Pompe disease is an autosomal recessive metabolic neuromuscular disorder caused by a deficiency of the lysosomal enzyme acid alpha-glucosidase (GAA). It has long been believed that the underlying pathology leading to tissue damage is caused by the enlargement and rupture of glycogen-filled lysosomes. Recent studies have also implicated autophagy, an intracellular lysosome-dependent degradation system, in the disease pathogenesis. In this study, we characterize the long-term impact of enzyme replacement therapy (ERT) with recombinant human GAA (rhGAA) on lysosomal glycogen accumulation and autophagy in some of the oldest survivors with classic infantile Pompe disease (IPD).

Methods

Muscle biopsies from 8 [4 female, 4 male; 6 cross-reactive immunologic material (CRIM)-positive, 2 CRIM-negative] patients with a confirmed diagnosis of classic IPD were examined using standard histopathological approaches. In addition, muscle biopsies were evaluated by immunostaining for lysosomal marker (lysosomal-associated membrane protein-2; LAMP2), autophagosomal marker (microtubule-associated protein 1 light chain 3; LC3), and acid and alkaline ATPases. All patients received rhGAA by infusion at cumulative biweekly doses of 20–40 mg/kg.

Results

Median age at diagnosis of classic IPD was 3.4 months (range: 0 to 6.5 months; n = 8). At the time of muscle biopsy, the patients’ ages ranged from 1 to 103 months and ERT duration ranged from 0 (i.e., baseline, pre-ERT) to 96 months. The response to therapy varied considerably among the patients: some patients demonstrated motor gains while others experienced deterioration of motor function, either with or without a period of initial clinical benefit. Skeletal muscle pathology included fiber destruction, lysosomal vacuolation, and autophagic abnormalities (i.e., buildup), particularly in fibers with minimal lysosomal enlargement. Overall, the pathology reflected clinical status.

Conclusions

This is the first study to investigate the impact of rhGAA ERT on lysosomal glycogen accumulation and autophagic buildup in patients with classic IPD beyond 18 months of treatment. Our findings indicate that ERT does not fully halt or reverse the underlying skeletal muscle pathology in IPD. The best outcomes were observed in the two patients who began therapy early, namely at 0.5 and 1.1 months of age.

Autophagy and mitochondria in Pompe disease: nothing is so new as what has long been forgotten

Macroautophagy (often referred to as autophagy) is an evolutionarily conserved intracellular system by which macromolecules and organelles are delivered to lysosomes for degradation and recycling. Autophagy is robustly induced in response to starvation in order to generate nutrients and energy through the lysosomal degradation of cytoplasmic components. Constitutive, basal autophagy serves as a quality control mechanism for the elimination of aggregated proteins and worn-out or damaged organelles, such as mitochondria. Research during the last decade has made it clear that malfunctioning or failure of this system is associated with a wide range of human pathologies and age-related diseases. Our recent data provide strong evidence for the role of autophagy in the pathogenesis of Pompe disease, a lysosomal glycogen storage disease caused by deficiency of acid alpha-glucosidase (GAA). Large pools of autophagic debris in skeletal muscle cells can be seen in both our GAA knockout model and patients with Pompe disease. In this review, we will focus on these recent data, and comment on the not so recent observations pointing to the involvement of autophagy in skeletal muscle damage in Pompe disease.

Early administration of enzyme replacement therapy for Pompe disease: short-term follow-up results

Pompe disease (glycogen storage disease II, OMIM # 232300), is a hereditary lysosomal disorder. It is characterized by deficiency of acid alpha-glucosidase enzyme (acid maltase, GAA, OMIM *606800, EC 3.1.26.2), secondary to mutations in the GAA gene (HGNC:4065) on chromosome 17q25.2-q25.3. Absent enzyme activity in the infantile form of Pompe disease results in abnormal glycogen deposition in the skeletal, cardiac, and smooth muscles, leading to hypertrophic cardiomyopathy, feeding abnormalities, hypotonia, weakness, respiratory insufficiency, and ultimately death. Prenatal diagnosis is accomplished by enzyme assay, mutation analysis or electron microscopy of amniotic fluid cells or chorionic villus sample. However, these techniques may not always be available, and can result in perinatal morbidity and fetal loss. Early diagnosis of Pompe disease results in early institution of enzyme replacement therapy (ERT), which minimizes morbidity and prolongs survival. We report the case of a 35-week part-of-twin neonate, whose older sibling died earlier because of infantile Pompe disease. At 32 weeks of gestation, fetal echocardiography showed hypertrophic cardiomyopathy in twin 1, which persisted until birth at 35 weeks of gestation. Diagnosis was confirmed after birth by enzyme assay, and mutation analysis showing homozygosity for the sequence change 1327-2A>G (GAA intr 8). Administration of ERT at 18 h of age, resulted in normalization of cardiac abnormalities within 21 weeks of therapy, and normal neurodevelopmental assessment at 46 weeks, using Griffiths Mental Development Scales. To our knowledge, this is the youngest patient reported to receive ERT for Pompe disease, and the first report of prenatal diagnosis of Pompe disease by fetal echocardiography.