Glycogenosis type II: a juvenile-specific mutation with an unusual splicing pattern and a shared mutation in African Americans

Transforming the clinical outcome in CRIM-negative infantile Pompe disease identified via newborn screening: the benefits of early treatment with enzyme replacement therapy and immune tolerance induction

Purpose:

To assess the magnitude of benefit to early treatment initiation, enabled by newborn screening or prenatal diagnosis, in patients with cross-reactive immunological material (CRIM)-negative infantile Pompe disease (IPD), treated with enzyme replacement therapy (ERT) and prophylactic immune tolerance induction (ITI) with rituximab, methotrexate, and IVIG.

Methods:

A total of 41 CRIM-negative IPD patients were evaluated. Amongst patients who were treated with ERT+ITI (n=30), those who were invasive ventilator-free at baseline and had ≥6 months of follow-up were stratified based on age at treatment initiation: 1) early (≤4 weeks), 2) intermediate (>4 and ≤15 weeks), and 3) late (>15 weeks). A historical cohort of 11 CRIM-negative patients with IPD treated with ERT monotherapy served as an additional comparator group.

Results:

Twenty patients were included; five, seven, and eight in early, intermediate, and late treatment groups, respectively. Genotypes were similar across the three groups. Early-treated patients showed significant improvements in left ventricular mass index, motor and pulmonary outcomes, as well as biomarkers creatine kinase and urinary glucose tetrasaccharide, compared to those treated later.

Conclusion:

Our preliminary data suggest that early treatment with ERT+ITI can transform the long-term CRIM-negative IPD phenotype, which represents the most severe end of the Pompe disease spectrum.

Incidence of infantile Pompe disease in the Maroon population of French Guiana

OBJECTIVES

The aim of this study was to describe the epidemiology of infantile Pompe disease (IPD) in French Guiana, a French overseas territory, by combining a retrospective case records study and a prospective anonymous genotyping in a sample of mothers followed in the two major maternity units of French Guiana.

METHODS

We identified 19 newborns with IPD born within a 13-year-period in French Guiana, corresponding to 1/4528 births. All children were born within the African-American Maroon (Bushinengue) community originating from slaves who settled along the Maroni river in the 19th century. We also performed an anonymised screening for all women in postpartum, in the two main maternity units of French Guiana.

RESULTS

Genetic investigations revealed that all patients with IPD were homozygotes or compound heterozygotes for two known pathogenic variations: c.2560C>T p.(Arg854*) that has already been reported in African-Americans and c.1942G>A p.(Gly648Ser), a rare previously considered to be variant. We identified no heterozygotes among 453 mothers of various ethnicities in Cayenne, but 15 heterozygotes among 425 mothers (1/27) in Saint-Laurent-du-Maroni (95% CI 1/45 to 1/17), all from the Maroon community, which corresponds to an expected IPD incidence in Maroons of 1/1727 (95% CI 1/1156 to 1/8100).

CONCLUSION

The incidence of IPD in the Maroon community is roughly 50 times higher than elsewhere in the world. The presence of only two different variants in all affected patients is compatible with a double founder effect in a relatively small population that has seldom mixed with other regional populations in the past and therefore has a reduced pool of genotypes.

Clinical Laboratory Experience of Blood CRIM Testing in Infantile Pompe Disease

Cross-reactive immunological material (CRIM) status is an important prognostic factor in patients with infantile Pompe disease (IPD) being treated with enzyme replacement therapy. Western blot analysis of cultured skin fibroblast lysates has been the gold standard for determining CRIM status. Here, we evaluated CRIM status using peripheral blood mononuclear cell (PBMC) protein. For 6 of 33 patients (18%) CRIM status determination using PBMC was either indeterminate or discordant with GAA genotype or fibroblast CRIM analysis results. While the use of PBMCs for CRIM determination has the advantage of a faster turnaround time, further evaluation is needed to ensure the accuracy of CRIM results.

The impact of antibodies in late-onset Pompe disease: a case series and literature review

Pompe disease (glycogen storage disease type II, GSD II) is an autosomal recessive disease caused by a deficiency of acid α-glucosidase (GAA), leading to lysosomal glycogen accumulation in various tissues, most notably cardiac, skeletal and smooth muscle. While both infantile and late-onset patients have benefited greatly from alglucosidase alfa (Myozyme®) enzyme replacement therapy (ERT), a subgroup of patients does not demonstrate as pronounced a response as others. Various factors have been identified which may help predict the response to ERT in infantile Pompe disease patients. High, sustained antibody titers (HSAT) have been correlated with poor response to ERT in infantile Pompe cases. However, the literature on the role of antibodies in the late-onset Pompe disease (LOPD) population is limited. Our literature review highlights the need for studies to explore the potential impact of antibodies in LOPD. Further supporting the importance of this issue, our retrospective chart review of sixty LOPD patients revealed that six of these sixty (10%) LOPD patients developed HSAT of ≥1:51,200 on two or more occasions at or beyond 6 months on ERT. Here, we present a series of three of these six LOPD patients for whom detailed antibody data and clinical data were available for greater than 1 year on ERT. These three patients developed HSAT corresponding with clinical decline as demonstrated by pulmonary function, quality of life, and motor function testing, affirming the development of HSAT in a subset of patients with LOPD, and its potentially negative impact on clinical response to ERT. The findings of our study and literature review lead us to conclude that there is a strong indication for systematic studies to accurately delineate the potential impact of antibodies in LOPD.

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.

Pompe disease: dramatic improvement in gastrointestinal function following enzyme replacement therapy. A report of three later-onset patients

Pompe disease is a lysosomal storage disease due to deficient acid α-glucosidase (GAA) activity. Infants with the classic infantile-onset subtype present with severe hypotonia and cardiomegaly, and most expire in the first year of life, whereas the severity of the muscle-based manifestations in patients with the late infantile/juvenile and adult-onset subtypes depends on the level of GAA residual enzymatic activity. The clinical features of later-onset Pompe disease are still emerging, and even the natural history and progression of muscle weakness and respiratory failure, hallmarks of the later-onset subtypes, are not well documented. For example, we report here three later-onset patients who had chronic diarrhea, postprandial bloating and abdominal pain, previously unrecognized manifestations of later-onset Pompe disease. Two patients had intestinal incontinence and one reported synchronous vomiting and diarrhea on a daily basis. These symptoms significantly interfered with their quality of life, often limiting their ability to leave home. All gastrointestinal symptoms resolved within the first six months of enzyme replacement therapy (ERT) with recombinant human alglucosidase alpha (rhGAA). All three patients gained weight and remain symptom free, two for over four years. Thus, gastrointestinal symptoms occur in later-onset patients with Pompe disease and are resolved with ERT.

Development of a clinical assay for detection of GAA mutations and characterization of the GAA mutation spectrum in a Canadian cohort of individuals with glycogen storage disease, type II

Glycogen storage disease, type II (GSDII; Pompe disease; acid maltase deficiency) is an autosomal recessive disease caused by mutations of the GAA gene that lead to deficient acid alpha-glucosidase enzyme activity and accumulation of lysosomal glycogen. Although measurement of acid alpha-glucosidase enzyme activity in fibroblasts remains the gold standard for the diagnosis of GSDII, analysis of the GAA gene allows confirmation of clinical or biochemical diagnoses and permits predictive and prenatal testing of individuals at risk of developing GSDII. We have developed a clinical molecular test for the detection of GAA mutations based on cycle sequencing of the complete coding region. GAA exons 2-20 are amplified in six independent PCR using intronic primers. The resulting products were purified and sequenced. Preliminary studies using this protocol were conducted with DNA from 21 GSDII-affected individuals from five centers across Canada. In total, 41 of 42 mutations were detected (96.7% detection rate). Mutations spanned intron 1 through exon 19 and included nine novel mutations. Haplotype analysis of recurrent mutations further suggested that three of these mutations are likely to have occurred independently at least twice. Additionally, we report the identification of the c.-32-13T>G GAA mutation in an individual with infantile variant GSDII, despite reports of this mutation being associated almost exclusively with late-onset forms of the disease. The development of a clinical molecular test provides an important tool for the management and counseling of families and individuals with GSDII, and has provided useful information about the GAA mutation spectrum in Canada.

Pompe disease: current state of treatment modalities and animal models

Pompe disease is a rare autosomal recessive lysosomal storage disease caused by deficiency of acid-alpha-glucosidase (GAA). This deficiency results in glycogen accumulation in the lysosomes, leading to lysosomal swelling, cellular damage and organ dysfunction. In early-onset patients (the classical infantile form and juvenile form) this glycogen accumulation leads to death. The only therapy clinically available is enzyme replacement therapy, which compensates for the missing enzyme by i.v. administration of recombinant produced enzyme. The development of clinically relevant animal models gained more insight in the disease and allowed evaluation of recombinant enzyme therapy. Several therapies are currently under investigation for Pompe disease, including gene therapy. This review gives an overview of the available knockout mouse models, of the in vitro and in vivo studies performed using recombinant produced enzyme. Furthermore, it describes current therapeutic approaches for Pompe disease as well as experimental therapies like gene correction therapy.

Two new missense mutations of GAA in late onset glycogen storage disease type II

Glycogen storage disease type II (GSD II) is an autosomal recessive disorder resulting from a deficiency of acid alpha-glucosidase (GAA, or acid maltase). In this study, we aimed to characterize phenotype and genotype in three patients with late onset GSD II in Korea. Clinically, all of our patients showed typical features of late onset GSD II with the reduced GAA enzyme activities. The respiratory difficulty preceding ambulatory failure seems to be one of the most remarkable clinical features characterizing late onset GSD II. By direct sequence analysis of PCR-amplified genomic DNA obtained from patients' skeletal muscle or peripheral leukocytes, we identified four missense mutations. Two of them (p.266Pro>Ser and p.439Met>Lys) were new missense mutations causing late onset GSD II, which had not been reported elsewhere before. One of them (p.439Met>Lys) was found in two alleles from each patient, suggesting it could be a recurrent mutation among Korean population.

Pompe disease (glycogen storage disease type II) in Argentineans: clinical manifestations and identification of 9 novel mutations

Pompe disease is an autosomal recessive disorder caused by a deficiency in 1,4-alpha-glucosidase (EC.3.2.1.3), the enzyme required to hydrolyze lysosomal glycogen to glucose. While previous studies have focused on Pompe patients from Europe, the United States, and Taiwan, we have analyzed a group of South American Pompe patients to better understand the molecular basis of their disease. From 14 Argentinean patients diagnosed with either infantile or late-onset disease, we identified 14 distinct mutations in the acid alpha-glucosidase (GAA) gene including nine novel variants (c.236_246del, c.377G>A, c.1099T>C, c.1397T>G, c.1755-1G>A, c.1802C>G, c.1978C>T, c.2281delGinsAT, and c.2608C>T). Three different families displayed the c.377G>A allelic variant, suggesting a higher frequency among a subset of Argentineans. Comparison of patients with similar or identical variations in the GAA gene highlights the phenotypic diversity of late-onset disease and supports a role for other genetic and environmental factors in disease presentation.

The natural course of infantile Pompe's disease: 20 original cases compared with 133 cases from the literature

OBJECTIVE

Infantile Pompe's disease is a lethal cardiac and muscular disorder. Current developments toward enzyme replacement therapy are promising. The aim of our study is to delineate the natural course of the disease to verify endpoints of clinical studies.

METHODS

A total of 20 infantile patients diagnosed by the collaborative Dutch centers and 133 cases reported in literature were included in the study. Information on clinical history, physical examination, and diagnostic parameters was collected.

RESULTS

The course of Pompe's disease is essentially the same in the Dutch and the general patient population. Symptoms start at a median age of 1.6 months in both groups. The median age of death is 7.7 and 6 months, respectively. Five percent of the Dutch patients and 8% of all reported patients survive beyond 1 year of age. Only 2 patients from literature became older than 18 months. A progressive cardiac hypertrophy is characteristic for infantile Pompe's disease. The diastolic thickness of the left ventricular posterior wall and cardiac weight at autopsy increase significantly with age. Motor development is severely delayed and major developmental milestones are generally not achieved. For the Dutch patient group, growth deviates significantly from normal despite start of nasogastric tube feeding. Levels of aspartate aminotransferase, alanine aminotransferase, lactate dehydrogenase, creatine kinase, or creatine kinase-myocardial band isoenzyme are typically elevated, although aspartate aminotransferase, alanine aminotransferase, and lactate dehydrogenase increase significantly with age. The patients have fully deleterious mutations. Acid alpha-glucosidase activity is severely deficient.

CONCLUSIONS

Survival, decrease of the diastolic thickness of the left ventricular posterior wall, and achievement of major motor milestones are valid endpoints for therapeutic studies of infantile Pompe's disease. Mutation analysis and measurement of the alpha-glucosidase activity should be part of the enrollment program.

Twenty-two novel mutations in the lysosomal ?-glucosidase gene (GAA) underscore the genotype-phenotype correlation in glycogen storage disease type II

Patients with glycogen storage disease type II (GSDII, Pompe disease) suffer from progressive muscle weakness due to acid alpha-glucosidase deficiency. The disease is inherited as an autosomal recessive trait with a spectrum of clinical phenotypes. We have investigated 29 cases of GSDII and thereby identified 55 pathogenic mutations of the acid alpha-glucosidase gene (GAA) encoding acid maltase. There were 34 different mutations identified, 22 of which were novel. All of the missense mutations and two other mutations with an unpredictable effect on acid alpha-glucosidase synthesis and function were transiently expressed in COS cells. The effect of a novel splice-site mutation was investigated by real-time PCR analysis. The outcome of our analysis underscores the notion that the clinical phenotype of GSDII is largely dictated by the nature of the mutations in the GAA alleles. This genotype-phenotype correlation makes DNA analysis a valuable tool to help predict the clinical course of the disease.

Identification of six novel mutations in the acid alpha-glucosidase gene in three Spanish patients with infantile onset glycogen storage disease type II (Pompe disease)

Glycogen storage disease type II is an autosomal recessive muscle disorder due to deficiency of lysosomal acid alpha-glucosidase and the resulting intralysosomal accumulation of glycogen. We found six novel mutations in three Spanish classic infantile onset glycogen storage disease type II patients with involvement of both cardiac and skeletal muscle; three missense mutations (G219R, E262K, M408V), a nonsense mutation (Y191X), a donor splice site mutation (IVS18 +2gt>ga) and an in frame deletion of an asparagine residue (nt1408-1410). The missense mutations were not found in 100 normal chromosomes and therefore are not normal polymorphic variants. The splice site mutation was subsequently detected in an additional 'Spanish' infantile onset glycogen storage disease type II patient from El Salvador. Further studies will be required to determine if the IVS18 +2gt>ga splice site mutation might in fact be a relatively common Spanish mutation. Mutations among Spanish glycogen storage disease type II patients appear to be genetically heterogeneous and differ from common mutations in neighboring countries.

Muscle glycogenoses

There are 11 hereditary disorders of glycogen metabolism affecting muscle alone or together with other tissues, and they cause two main clinical syndromes: episodic, recurrent exercise intolerance with cramps, myalgia, and myoglobinuria; or fixed, often progressive weakness. Great strides have been made in our understanding of the molecular bases of these disorders, all of which show remarkable genetic heterogeneity. In contrast, the pathophysiological mechanisms underlying acute muscle breakdown and chronic weakness remain unclear. Although glycogen storage diseases have been studied for decades, new biochemical defects are still being discovered, especially in the glycolytic pathway. In addition, the pathogenesis of polyglucosan deposition is being clarified both in traditional glycogenoses and in disorders such as Lafora's disease. In some conditions, combined dietary and exercise regimens may be of help, and gene therapy, including recombinant enzyme replacement, is being actively pursued.

Aberrant splicing at catalytic site as cause of infantile onset glycogen storage disease type II (GSDII): molecular identification of a novel IVS9 (+2GT-->GC) in combination with rare IVS10 (+1GT-->CT)

Glycogen storage disease type II (GSDII) results from deleterious mutations in acid alpha-glucosidase gene. To date several mutant alleles have been studied including missense and nonsense mutations, insertions, small and large deletions as well as splice site mutations. Apart from IVS1 (- 13-->G), 525delT, and Delta18, the other mutations are rare and often unique to single patients. Moreover, the molecular findings also observed in the different ethnic groups makes it difficult to attempt to correlate genotype and phenotype to explain the origin of clinical variability. Even though there are no conclusive genotype phenotype correlations, the in frame splice site mutations identified up until now have been found associated with the juvenile/adult onset of GSDII. In this study we describe a novel in frame splicing defect, IVS9 (+2GT-->GC), identified in combination with the rare IVS10 (+1GT-->CT) mutation in a patient with classic infantile GSDII disease. Because both mutations occur at the catalytic site region, it is likely that the alteration of both catalytic function and steric conformation of the enzyme may be responsible for the most severe form of the disease.

Polymorphism of the endoglin gene in patients with intracranial saccular aneurysms

OBJECT

Endoglin, a transforming growth factor beta-binding protein, is a glycoprotein expressed on the surface of human vascular endothelial cells. Mutations of this gene are responsible for hereditary hemorrhagic telangiectasis and are associated with sporadic intracerebral hemorrhage as a risk factor. The purpose of this study was to examine the polymorphism of this gene in patients with intracranial aneurysms.

METHODS

The authors identified the mutations and insertion polymorphism around exon 7 of the endoglin gene in 82 patients with intracranial saccular aneurysms (aneurysm group) and 114 control volunteers (control group). A 6-base insertion (GGGGGA) was found in intron 7 at 26 bases beyond the 3' end of exon 7. The homozygous insertion of intron 7 of the gene was present in 20.7% of the aneurysm group compared with 6.1% of the control group (chi2 = 9.837, p = 0.0073). The insertion allele frequency was significantly higher in the aneurysm group (67 [40.8%] of 164) than that in the control group (63 [27.6%] of 228) (chi2 = 7.48, p = 0.0062). The most notable clinical characteristic of the 17 patients with homozygous insertion in the aneurysm group was the relatively high percentage of patients with hypertension and of those with multiple aneurysms.

CONCLUSIONS

The data provide evidence of an association between aneurysm development and a polymorphism at a genetic variant of endoglin in patients with these lesions.

Glycogen storage diseases of muscle

Ten specific enzyme defects of glycogen metabolism affect skeletal muscle alone or in combination with other tissues. The newest addition to this group of disorders is the defect of aldolase A (glycogenosis type XII), a block in terminal glycolysis associated with myopathy and a hemolytic trait. The muscle glycogenoses cause two major syndromes, one characterized by exercise intolerance, cramps, and myoglobinuria, and the other dominated by fixed, often progressive weakness. This review considers sequentially recent advances in the following: clinical features or clinical variants, including a brief description of glycogenosis type XII; animal models, both spontaneous and genetically engineered; physiopathologic mechanisms, especially of the exercise intolerance and myoglobinuria; biochemical and molecular features--molecular defects are just beginning to be discovered for some glycogenoses (e.g. phosphorylase-b-kinase deficiency or branching enzyme deficiency), whereas they form long lists for others, such as acid maltase deficiency and myophosphorylase deficiency; and therapeutic approaches, including enzyme replacement and gene therapy.

Targeted disruption of the acid alpha-glucosidase gene in mice causes an illness with critical features of both infantile and adult human glycogen storage disease type II

We have used gene targeting to create a mouse model of glycogen storage disease type II, a disease in which distinct clinical phenotypes present at different ages. As in the severe human infantile disease (Pompe Syndrome), mice homozygous for disruption of the acid alpha-glucosidase gene (6(neo)/6(neo)) lack enzyme activity and begin to accumulate glycogen in cardiac and skeletal muscle lysosomes by 3 weeks of age, with a progressive increase thereafter. By 3.5 weeks of age, these mice have markedly reduced mobility and strength. They grow normally, however, reach adulthood, remain fertile, and, as in the human adult disease, older mice accumulate glycogen in the diaphragm. By 8-9 months of age animals develop obvious muscle wasting and a weak, waddling gait. This model, therefore, recapitulates critical features of both the infantile and the adult forms of the disease at a pace suitable for the evaluation of enzyme or gene replacement. In contrast, in a second model, mutant mice with deletion of exon 6 (Delta6/Delta6), like the recently published acid alpha-glucosidase knockout with disruption of exon 13 (Bijvoet, A. G., van de Kamp, E. H., Kroos, M., Ding, J. H., Yang, B. Z., Visser, P., Bakker, C. E., Verbeet, M. P., Oostra, B. A., Reuser, A. J. J., and van der Ploeg, A. T. (1998) Hum. Mol. Genet. 7, 53-62), have unimpaired strength and mobility (up to 6.5 months of age) despite indistinguishable biochemical and pathological changes. The genetic background of the mouse strains appears to contribute to the differences among the three models.