Seven cases of Pompe disease from Greece

Body composition and 6 minute walking ability in late-onset pompe disease patients after 9 years of enzyme replacement therapy

OBJECTIVE

Pompe disease is a rare autosomal recessive disorder caused by the deficiency of acid α-glycosidase resulting in accumulation of glycogen in the lysosomes. The late-onset form of the disease (LOPD) causes primarily progressive muscle weakness and respiratory insufficiency. Enzyme replacement therapy (ERT) introduced in 2006, showed mild improvement or stabilization of the symptoms although long-term data are limited. Aim of the study was to describe the progression of body composition and walking ability in LOPD patients receiving ERT consistently for 9 years.

METHODS

Lean body mass, bone mineral density, body fat and 6 min walking distance were assessed in three male and three female LOPD patients (height 165.8 ± 11.2 cm, age 42.3 ± 11.8yrs, body mass 71.1 ± 20.8 kg, at study entry), every three years, for 9 years since ERT initiation (T0, T3, T6, T9).

RESULTS

Total body and upper extremities' lean mass remained unchanged (p < 0.05), but it was decreased for the lower extremities (T3:13.06 ± 3.848 kg vs. T9:11.63 ± 3.49 kg, p < 0.05). Lean body mass was not significantly different after 9 years of ERT compared to before the ERT initiation (T0 to T9). Bone mineral density remained unchanged. Percent body fat increased (T0:39.1 ± 10.3%, vs. T9:43.1 ± 10.4%, p < 0.05). Six minute walking distance tended to increase after 3 years of ERT and decreased gradually thereafter, with no difference between T0-T9. Lean mass of the lower extremities adjusted for body weight was significantly correlated with 6 min walking distance (r = 0.712, p < 0.05).

CONCLUSION

The current data show that enzyme replacement therapy may preserve lean body mass, bone mineral density and walking capacity in LOPD patients.

Correlation of GAA Genotype and Acid-α-Glucosidase Enzyme Activity in Hungarian Patients with Pompe Disease

Pompe disease is caused by the accumulation of glycogen in the lysosomes due to a deficiency of the lysosomal acid-α-glucosidase (GAA) enzyme. Depending on residual enzyme activity, the disease manifests two distinct phenotypes. In this study, we assess an enzymatic and genetic analysis of Hungarian patients with Pompe disease. Twenty-four patients diagnosed with Pompe disease were included. Enzyme activity of acid-α-glucosidase was measured by mass spectrometry. Sanger sequencing and an MLPA of the GAA gene were performed in all patients. Twenty (83.33%) patients were classified as having late-onset Pompe disease and four (16.66%) had infantile-onset Pompe disease. Fifteen different pathogenic GAA variants were detected. The most common finding was the c.-32-13 T > G splice site alteration. Comparing the α-glucosidase enzyme activity of homozygous cases to the compound heterozygous cases of the c.-32-13 T > G disease-causing variant, the mean GAA activity in homozygous cases was significantly higher. The lowest enzyme activity was found in cases where the c.-32-13 T > G variant was not present. The localization of the identified sequence variations in regions encoding the crucial protein domains of GAA correlates with severe effects on enzyme activity. A better understanding of the impact of pathogenic gene variations may help earlier initiation of enzyme replacement therapy (ERT) if subtle symptoms occur. Further information on the effect of GAA gene variation on the efficacy of treatment and the extent of immune response to ERT would be of importance for optimal disease management and designing effective treatment plans.

Update of the Pompe variant database for the prediction of clinical phenotypes: Novel disease-associated variants, common sequence variants, and results from newborn screening

Pompe disease is an inherited disorder caused by disease-associated variants in the acid α-glucosidase gene (GAA). The Pompe disease GAA variant database (http://www.pompevariantdatabase.nl) is a curated, open-source, disease-specific database, and lists disease-associated GAA variants, in silico predictions, and clinical phenotypes reported until 2016. Here, we provide an update to include 226 disease-associated variants that were published until 2020. We also listed 148 common GAA sequence variants that do not cause Pompe disease. GAA variants with unknown severity that were identified only in newborn screening programs were listed as a new feature to indicate the reason why phenotypes were still unknown. Expression studies were performed for common missense variants to predict their severity. The updated Pompe disease GAA variant database now includes 648 disease-associated variants, 26 variants from newborn screening, and 237 variants with unknown severity. Regular updates of the Pompe disease GAA variant database will be required to improve genetic counseling and the study of genotype-phenotype relationships.

Vacuolated PAS-positive lymphocytes as an hallmark of Pompe disease and other myopathies related to impaired autophagy

Autosomal recessive Pompe disease is a lysosomal disorder caused by mutations of the acid-α-glucosidase (GAA) gene. Deficiency of GAA enzyme leads to glycogen accumulation and autophagy impairment in cardiac and skeletal muscles, but also in lymphocytes. Since an effective therapy is available, a rapid, sensitive, and specific test is crucial to early identify affected subjects. Number of lymphocytes containing PAS-positive vacuoles was evaluated on blood films from 72 consecutive adult patients with hyperckemia and/or muscle weakness, 13 genetically confirmed late-onset-Pompe-disease (LOPD) and 13 of their offspring. GAA activity, measured on dried blood spot (DBS) in all patients inversely correlated with number of PAS-positive lymphocytes. More than 4 PAS-positive lymphocytes were found in 11 out of the 72 patients (6 new diagnosis of LOPD, 3 different glycogen storage myopathies, 1 glucose-6-phosphate dehydrogenase deficiency, 1 caveolinopathy), in all 13 LOPD patients and in the 13 LOPD offspring. These latter resulted to have all a single GAA mutation but low GAA levels. Immunostaining with the autophagy markers LC3 and p62 confirmed the autophagic nature of lymphocytes vacuoles. ROC curve assessment of PAS-positive lymphocytes disclosed 100% of sensitivity and 94% of specificity in recognizing both compound heterozygous and heterozygous GAA carriers. The other myopathies with more than 4 PAS-positive lymphocytes appeared to be all related to impaired autophagy, which seems to be responsible of PAS-positive vacuolated lymphocytes formation. Quantification of PAS-positive lymphocytes in blood films is useful to identify autophagic vacuolar myopathies and should be routinely used as first level test for Pompe disease.

From Cryptic Toward Canonical Pre-mRNA Splicing in Pompe Disease: a Pipeline for the Development of Antisense Oligonucleotides

While 9% of human pathogenic variants have an established effect on pre-mRNA splicing, it is suspected that an additional 20% of otherwise classified variants also affect splicing. Aberrant splicing includes disruption of splice sites or regulatory elements, or creation or strengthening of cryptic splice sites. For the majority of variants, it is poorly understood to what extent and how these may affect splicing. We have identified cryptic splicing in an unbiased manner. Three types of cryptic splicing were analyzed in the context of pathogenic variants in the acid α-glucosidase gene causing Pompe disease. These involved newly formed deep intronic or exonic cryptic splice sites, and a natural cryptic splice that was utilized due to weakening of a canonical splice site. Antisense oligonucleotides that targeted the identified cryptic splice sites repressed cryptic splicing at the expense of canonical splicing in all three cases, as shown by reverse-transcriptase-quantitative polymerase chain reaction analysis and by enhancement of acid α-glucosidase enzymatic activity. This argues for a competition model for available splice sites, including intact or weakened canonical sites and natural or newly formed cryptic sites. The pipeline described here can detect cryptic splicing and correct canonical splicing using antisense oligonucleotides to restore the gene defect.

Combination of two different homozygote mutations in Pompe disease

Pompe disease (OMIM no 232300) is an autosomal recessive inherited metabolic disorder, caused by glycogen accumulation in the lysosome due to deficiency of the lysosomal acid 03B1-glucosidase enzyme. Here we report the case of an 8-month-old girl of consanguineous Turkish parents, who was diagnosed with the infantile form of Pompe disease. Two different uncommon homozygote mutations (c.32-13 T > G homozygote and c.1856G > A homozygote) were detected. The patient had a more progressive clinical course than expected. We emphasize the rare combination of genetic mutations in this Turkish family with Pompe disease.

Identification and characterization of aberrant GAA pre-mRNA splicing in pompe disease using a generic approach

Identification of pathogenic variants in monogenic diseases is an important aspect of diagnosis, genetic counseling, and prediction of disease severity. Pathogenic mechanisms involved include changes in gene expression, RNA processing, and protein translation. Variants affecting pre-mRNA splicing are difficult to predict due to the complex mechanism of splicing regulation. A generic approach to systematically detect and characterize effects of sequence variants on splicing would improve current diagnostic practice. Here, it is shown that such approach is feasible by combining flanking exon RT-PCR, sequence analysis of PCR products, and exon-internal quantitative RT-PCR for all coding exons. Application of this approach to one novel and six previously published variants in the acid-alpha glucosidase (GAA) gene causing Pompe disease enabled detection of a total of 11 novel splicing events. Aberrant splicing included cryptic splice-site usage, intron retention, and exon skipping. Importantly, the extent of leaky wild-type splicing correlated with disease onset and severity. These results indicate that this approach enables sensitive detection and in-depth characterization of variants affecting splicing, many of which are still unrecognized or poorly understood. The approach is generic and should be adaptable for application to other monogenic diseases to aid in improved diagnostics.

Extended phenotype description and new molecular findings in late onset glycogen storage disease type II: a northern Italy population study and review of the literature

Glycogen storage disease type II (GSDII) is a lysosomal storage disorder caused by acid alpha-1,4-glucosidase deficiency and associated with recessive mutations in its coding gene GAA. Few studies have provided so far a detailed phenotypical characterization in late onset GSDII (LO-GSDII) patients. Genotype-phenotype correlation has been previously attempted with controversial results. We aim to provide an in-depth description of a cohort (n = 36) of LO-GSDII patients coming from the north of Italy and compare our population's findings to the literature. We performed a clinical record-based retrospective and prospective study of our patients. LO-GSDII in our cohort covers a large variability of phenotype including subtle clinical presentation and did not differ significantly from previous data. In all patients, molecular analysis disclosed GAA mutations, five of them being novel. To assess potential genotype-phenotype correlations we divided IVS1-32-13T>G heterozygous patients into two groups following the severity of the mutations on the second allele. Our patients harbouring "severe" mutations (n = 21) presented a strong tendency to have more severe phenotypes and more disability, more severe phenotypes and more disability, higher prevalence of assisted ventilation and a shorter time of evolution to show it. The determination of prognostic factors is mandatory in order to refine the accuracy of prognostic information, to develop follow-up strategy and, more importantly, to improve the decision algorithm for enzyme replacement therapy administration. The demonstration of genotype-phenotype correlations could help to reach this objective. Clinical assessment homogeneity is required to overcome limitations due to the lack of power of most studies.

Distinct disease phenotypes linked to different combinations of GAA mutations in a large late-onset GSDII sibship

Background

Glycogenosis type II (GSDII or Pompe disease) is an autosomal recessive disease, often characterized by a progressive accumulation of glycogen within lysosomes caused by a deficiency of α-1,4-glucosidase (GAA; acid maltase), a key enzyme of the glycogen degradation pathway. To date, more than 326 different mutations in the GAA gene have been identified in patients with GSDII but the course of the disease is difficult to be predicted on the basis of molecular genetic changes. Studies on large informative families are advisable to better define how genetics and non genetics factors like exercise and diet may influence the clinical phenotype.

Methods and results

In this study, we report on clinical, instrumental, and pathological features as well as on molecular analysis of a family with 10 out of 13 siblings affected by late-onset Pompe disease. Three mutations segregated in the family, two of which are novel mutations. Siblings showing a more severe phenotype were compound heterozygous for c.118C > T [p.R40X] and c.2647-7G > A [p.N882fs] on GAA, whereas, two patients showing a mild phenotype were compound heterozygous c.2647-7G > A [p.N882fs] and c.2276G > C [p.G759A] mutations. Quantitative expression analysis showed, in the patients carrying p.R40X/ p.N882fs, a significant (p 0.01) correlation between the levels of expression of the mutated allele and the age at onset of the disease.

Conclusions

As far as we know, this is the largest informative family with late-onset Pompe disease described in the literature showing a peculiar complex set of mutations of GAA gene that may partially elucidate the clinical heterogeneity of this family.

Newborn screening for lysosomal storage disorders in hungary

Even though lysosomal storage disorders (LSDs) are considered to be orphan diseases, they pose a highly relevant cause for morbidity and mortality as their cumulative prevalence is estimated to be 1:4,000. This is especially important as treatment in form of enzyme replacement therapy, substrate reduction therapy or stem cell transplantation is amenable for some LSDs. It is plausible that an early start of treatment might improve the overall prognosis and, even more important, prevent irreversible damage of key organs. To get a more precise insight into the real frequency of some LSDs in the general population, we screened 40,024 samples from the Hungarian newborn screening (NBS) program in Szeged for Fabry disease (FD), Gaucher disease (GD), Pompe disease (PD), and Niemann-Pick A/B (NPB) disease using tandem mass spectrometry. Altogether, 663 samples (1.66%) were submitted for retesting. Genetic confirmation was carried out for 120 samples with abnormal screening results after retesting, which identified three cases of GD, three cases of FD, nine cases of PD, and two cases with NPB. In some cases, we detected up to now unknown mutations - one in NPB and seven in PD - which raise questions about the clinical consequences of a NBS in the sense of late-onset manifestations. Overall, we conclude that screening for LSDs by tandem MS/MS followed by a genetic workup in identified patients is a robust, easy, valid, and feasible technology in newborn screening programs. Furthermore, early diagnosis of LSDs gives a chance to early treatment, but needs more clinical long-term data especially regarding the consequence of private mutations.

Effect of aerobic and resistance exercise training on late-onset Pompe disease patients receiving enzyme replacement therapy

Pompe disease is a rare autosomal recessive disorder characterized by the deficiency of acid α-glycosidase resulting in lysosomal accumulation of glycogen. The late-onset disease form is characterized by progressive skeletal and respiratory muscle dysfunction. In addition to the recently introduced enzyme replacement therapy (ERT), treatments such as protein-enriched diet and exercise training have been proposed, although little is known about their effectiveness on the physical condition of such patients. Aim of the present study was to investigate the effect of exercise training on muscular strength and body composition in five patients with late-onset Pompe disease receiving ERT. All subjects followed a 20 week lasting program of supervised aerobic and progressive resistance exercise training. Before and after the training period, body composition was determined with dual X-ray absorptiometry and isometric muscular strength was measured with a specialized load transducer. Functional capacity was assessed using the 6-min shuttle walk test. A significant increase in muscular strength (15-50% at various body parts, p<0.05) and 6-minute walking distance (203.8 ± 177 m before vs. 248.2 ± 184 m after, p<0.01) was observed after training, whereas total and lower extremities lean body mass did not change significantly. These results suggest that exercise training has a positive effect on muscular strength and functional capacity in patients on ERT with late-onset Pompe disease.

Adult Pompe disease: clinical manifestations and outcome of the first Greek patients receiving enzyme replacement therapy

OBJECTIVE

Pompe disease is an autosomal recessive lysosomal disorder caused by α-glucosidase deficiency. A specific treatment for the disease with enzyme replacement therapy is currently available. The aim of the present study is to describe the clinical manifestations and the effect of treatment in the first Greek patients with the adult form of the disease.

METHODS

Five Greek patients with adult onset Pompe disease aged between 40 and 73 years received 20 mg/kg Myozyme intravenously at two weekly intervals over a different period. Clinical and functional parameters were longitudinally registered.

RESULTS

Proximal muscle weakness and respiratory insufficiency were the most common manifestations of the disease, but their severity was different even among patients with similar genotype. The effect of treatment varied with most patients experiencing some improvement in muscle strength and fatigability, while the most severely affected patient did not benefit and stopped therapy.

CONCLUSION

No clear genotype-phenotype correlation emerges from our study. The different effect of treatment on our patients seems to be mainly related to their pre-treatment condition and can be reliably assessed only on a long term basis.

Splicing mutations in glycogen-storage disease type II: evaluation of the full spectrum of mutations and their relation to patients' phenotypes

Glycogen-storage disease type II is an autosomal recessive-inherited disorder due to the deficiency of acid α-glucosidase. A large number of mutations in the acid α-glucosidase gene have been described to date. Among them, ~15% are variations that may affect mRNA splicing process. In this study, we have for the first time comprehensively reviewed the available information on splicing mutations of the acid α-glucosidase gene and we have evaluated their possible impact on the splicing process using different in silico approaches. Out of the 39 different GAA-sequence variations described, an in silico analysis using seven different programs showed that 97% of them are predicted to have an impact on the splicing process. Moreover, this analysis showed a quite good correlation between the impact of the mutation on the splicing process and the clinical phenotype. In addition, we have performed the functional characterization of three novel sequence variants found in Italian patients and still uncharacterized. Using a minigene system, we have confirmed their pathogenic nature. In conclusion, this study has shown that in silico analysis represents a useful tool to select mutations that affect the splicing process of the acid α-glucosidase gene and provides an updated picture of all this kind of mutations reported till now.