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

Genotype, phenotype and treatment outcomes of 17 Malaysian patients with infantile-onset Pompe disease and the identification of 3 novel GAA variants

BACKGROUND

Pompe disease is a rare glycogen storage disorder caused by deficiency of the lysosomal enzyme acid alpha-glucosidase (GAA), leading to glycogen deposition in multiple tissues. Infantile-onset Pompe disease (IOPD) patients present within the first year of life with profound hypotonia and hypertrophic cardiomyopathy. Treatment with enzyme replacement therapy (ERT) has significantly improved survival for this otherwise lethal disorder. This study aims to describe the clinical and molecular spectrum of Malaysian IOPD patients, and to analyze their long term treatment outcomes.

METHODS

Seventeen patients diagnosed with IOPD between 2000 and 2020 were included in this retrospective cohort study. Clinical and biochemical data were collated and analyzed using descriptive statistics. GAA enzyme levels were performed on dried blood spots. Molecular analysis of the GAA gene was performed by polymerase chain reaction and Sanger sequencing. Structural modelling was used to predict the effect of the novel mutations on enzyme structure.

RESULTS

Our cohort had a median age of presentation of 3 months and median age of diagnosis of 6 months. Presenting features were hypertrophic cardiomyopathy (100%), respiratory insufficiency (94%), hypotonia (88%), failure to thrive (82%), feeding difficulties (76%), and hepatomegaly (76%). Fourteen different mutations in the GAA gene were identified, with three novel mutations, c.1552-14_1552-1del, exons 2-3 deletion and exons 6-10 deletion. The most common mutation identified was c.1935C > A p.(D645E), with an allele frequency of 33%. Sixteen patients received ERT at the median age of 7 months. Overall survival was 29%. Mean age of death was 17.5 months. Our longest surviving patient has atypical IOPD and is currently 20 years old.

CONCLUSIONS

This is the first study to analyze the genotype and phenotype of Malaysian IOPD patients, and has identified the c.1935C > A p.(D645E) as the most common mutation. The three novel mutations reported in this study expands the mutation spectrum for IOPD. Our low survival rate underscores the importance of early diagnosis and treatment in achieving better treatment outcomes.

Novel Mutation in the Feline GAA Gene in a Cat with Glycogen Storage Disease Type II (Pompe Disease)

Glycogen storage disease type II (Pompe disease: PD) is an autosomal recessively inherited fatal genetic disorder that results from the deficiency of a glycogen hydrolyzing enzyme, acid α-glucosidase encoded by the GAA gene. Here, we describe the molecular basis of genetic defects in an 8-month-old domestic short-haired cat with PD. The cat was previously diagnosed with PD based on the clinical and pathological findings of hypertrophic cardiomyopathy and excessive accumulation of glycogen in the cardiac muscles. Sanger sequencing was performed on 20 exons of the feline GAA gene using genomic DNA extracted from paraffin-embedded liver tissues. The affected cat was found to be homozygous for the GAA:c.1799G>A mutation resulting in an amino acid substitution (p.R600H) of acid α-glucosidase, a codon position of which is identical with three missense mutations (p.R600C, p.R600L, and p.R600H) causing human infantile-onset PD (IOPD). Several stability and pathogenicity predictors have also shown that the feline mutation is deleterious and severely decreases the stability of the GAA protein. The clinical, pathological, and molecular findings in the cat were similar to those of IOPD in humans. To our knowledge, this is the first report of a pathogenic mutation in a cat. Feline PD is an excellent model for human PD, especially IOPD.

Pompe disease ascertained through The Lantern Project, 2018-2021: Next-generation sequencing and enzymatic testing to overcome obstacles to diagnosis

The Lantern Project is an ongoing complimentary diagnostic program for patients in the United States sponsored by Sanofi and implemented by PerkinElmer Genomics. It combines specific enzymatic, biomarker, and genetic testing to facilitate rapid, accurate laboratory diagnosis of Pompe disease and several other lysosomal storage diseases, and a multigene next-generation sequencing panel including Pompe disease, LGMD, and other neuromuscular disorders. This article reports data for Pompe disease collected from October 2018 through December 2021, including acid α-glucosidase (GAA) enzyme assay and GAA sequencing (standard or expedited for positive newborn screening [NBS] to rule out infantile-onset Pompe disease [IOPD]) and the Focused Neuromuscular Panel, which includes GAA. One hundred forty patients (12 received only GAA enzyme testing, 128 had GAA sequencing alone or in addition to enzyme assay) have been confirmed with Pompe disease in this project. Eight of the 140 had a variant of unknown significance, but GAA activity ≤2.10 μmol/L/h, thus were confirmed with Pompe disease. Three diagnosed patients 0-2 years old had cross-reactive immunologic material (CRIM)-negative GAA variants and thus IOPD. One additional infant with presumptive IOPD had a homozygous frameshift c.1846del, likely CRIM-negative; symptoms were not provided. Among the 128 patients with molecular results, the c.-32-13T>G splice variant was homozygous in 11, compound-heterozygous in 98, and absent in 19. Proximal muscle weakness (58 patients) was the most common sign reported at testing; elevated creatine kinase (29 patients) was the most common laboratory result. The most common symptom categories were muscular (73 patients), musculoskeletal (13 patients), and respiratory (23 patients). Clinical information was not available for 42 samples, and 17 infants had only "abnormal NBS" or "low GAA" reported. Cardiac symptoms in 7 included potentially age-related conditions in five c.-32-13T>G-compound-heterozygous adults (myocardial infarction, heart murmur/palpitations, congestive heart failure: 1 each; 2 with atrial fibrillation) and hypertrophic cardiomyopathy in 2 children (1 and 2 years old) with presumptive IOPD. One novel GAA variant was observed in a patient with enzyme activity 0.31 μmol/L/h: c.1853_1854ins49, a frameshift pathogenic variant. The Lantern Project demonstrates the combinatorial utility of enzyme assay, targeted single-gene testing, and a focused neuromuscular next-generation sequencing panel in diagnosing Pompe disease.

LMNA-related muscular dystrophy: Identification of variants in alternative genes and personalized clinical translation

Background: Laminopathies are caused by rare alterations in LMNA, leading to a wide clinical spectrum. Though muscular dystrophy begins at early ages, disease progression is different in each patient. We investigated variability in laminopathy phenotypes by performing a targeted genetic analysis of patients diagnosed with LMNA-related muscular dystrophy to identify rare variants in alternative genes, thereby explaining phenotypic differences. Methods: We analyzed 105 genes associated with muscular diseases by targeted sequencing in 26 pediatric patients of different countries, diagnosed with any LMNA-related muscular dystrophy. Family members were also clinically assessed and genetically analyzed. Results: All patients carried a pathogenic rare variant in LMNA. Clinical diagnoses included Emery-Dreifuss muscular dystrophy (EDMD, 13 patients), LMNA-related congenital muscular dystrophy (L-CMD, 11 patients), and limb-girdle muscular dystrophy 1B (LGMD1B, 2 patients). In 9 patients, 10 additional rare genetic variants were identified in 8 genes other than LMNA. Genotype-phenotype correlation showed additional deleterious rare variants in five of the nine patients (3 L-CMD and 2 EDMD) with severe phenotypes. Conclusion: Analysis f known genes related to muscular diseases in close correlation with personalized clinical assessments may help identify additional rare variants of LMNA potentially associated with early onset or most severe disease progression.

Detection of Structural Variants by NGS: Revealing Missing Alleles in Lysosomal Storage Diseases

Lysosomal storage diseases (LSDs) are a heterogeneous group of rare multisystem metabolic disorders occurring mostly in infancy and childhood, characterized by a gradual accumulation of non-degraded substrates inside the cells. Although biochemical enzymatic assays are considered the gold standard for diagnosis of symptomatic patients, genotyping is a requirement for inclusion in enzyme replacement programs and is a prerequisite for carrier tests in relatives and DNA-based prenatal diagnosis. The emerging next-generation sequencing (NGS) technologies are now offering a powerful diagnostic tool for genotyping LSDs patients by providing faster, cheaper, and higher-resolution testing options, and are allowing to unravel, in a single integrated workflow SNVs, small insertions and deletions (indels), as well as major structural variations (SVs) responsible for the pathology. Here, we summarize the current knowledge about the most recurrent and private SVs involving LSDs-related genes, review advantages and drawbacks related to the use of the NGS in the SVs detection, and discuss the challenges to bring this type of analysis in clinical diagnostics.

Classic infantile-onset Pompe disease with histopathological neurologic findings linked to a novel GAA gene 4 bp deletion: A case study

Pompe disease (PD) is an autosomal recessive disorder by a deficiency of acid α‐glucosidase (GAA) with intralysosomal glycogen accumulation in multiple tissues. We present the case of a 5‐month‐old male with hypertrophic cardiomyopathy, hypotony, feeding difficulties, and oxygen requirement since birth. At 3 months of age, he develops heart failure, respiratory impairment, and neurological deterioration. The echocardiogram revealed concentric hypertrophic cardiomyopathy with left‐diastolic dysfunction. We found increased creatine‐phosphokinase, lactate dehydrogenase, and urinary glucose tetrasaccharide levels, 50% of PAS‐positive vacuolated lymphocytes in the peripheral blood smear, and low GAA activity. Sequencing of coding exons and flanking intronic sequences revealed a novel homozygous 4 bp deletion in exon 15 of the GAA gene (c.2066_2069delAGCC/p.Glu689Glyfs*6). IOPD was diagnosed. At 5 months old, we started enzyme replacement therapy with an alpha‐alglucosidase of 20 mg/kg weekly and immunomodulation with intravenous immunoglobulin. He developed two cardiorespiratory arrests with subsequent neurologic deterioration, convulsive crisis, and respiratory failure and died at 9 months old. We found the usual PD hallmarks in the heart, striated muscle, and liver but also we found neuronal lesions characterized by cytoplasm vacuolization with PAS‐positive granules in the central nervous system and myenteric plexus. We describe a novel GAA gene pathogenic variant with a particular phenotype characterized by classic IOPD and neurologic histopathological findings. Enhancing the knowledge of lysosomal diseases is critical to improving the diagnosis and treatment of these patients.

Genetic analysis of 76 Spanish Pompe disease patients: Identification of 12 novel pathogenic GAA variants and functional characterization of splicing variants

Glycogenosis type II (GSDII), or Pompe disease (MIM 232300), is an inherited autosomal recessive disorder caused by deficiency of the lysosomal acid-α-glucosidase. Mutations in the GAA gene alter normal enzyme production and lead to progressive buildup of intralysosomal glycogen, which plays an essential role in the severity and progression of the disease. We report here the study of 76 patients from Spain with either infantile or late onset form of Pompe disease. The analysis consisted in the molecular study of exons and intron flanking fragments of GAA gene. We have identified 55 different molecular pathogenic variants, 12 of them not previously described. In addition, we have determined a frequency of 84.37% for the c.-32-13T>G mutation in patients with the late-onset form of the disease. Functional characterization of some splice mutations showed deleterious mechanisms on the processing of mRNA.

Genotype-phenotype correlation of 17 cases of Pompe disease in Spanish patients and identification of 4 novel GAA variants

Background

Pompe disease (PD) is an autosomal recessive metabolic disorder caused by pathogenic variants in the acid -glucosidase gene (GAA) that produces defects in the lysosomal acid -1,4-glucosidase. We aimed to identify genetic variations and clinical features in Spanish subjects to establish genotypephenotype correlation.

Methods

A total of 2637 samples of patients who showed symptoms or susceptible signs of PD were enrolled in this observational study. Enzymatic activity was detected by fluorometric techniques and the genetic study was carried out using Next-Generation Sequencing.

Results

Fourteen different variants from 17 diagnosed patients were identified, seven males and nine females with LOPD (mean age 36.07, SD 20.57, range 764) and a 2-day-old boy with IOPD, four genetic variants had not been described in the literature previously, including a homozygous variant. In all of them -glucosidase activity was decreased. Muscle weakness, respiratory distress, exercise intolerance, hypotonia, dysphagia and myalgia were commonly observed in patients.

Conclusions

This study report four new genetic variants that contribute to the pathogenic variants spectrum of the GAA gene. We confirm that patients in Spain have a characteristic profile of a European population, with c.-32-13T>G being the most prevalent variant. Furthermore, it was confirmed that the c.236_246delCCACACAGTGC pathogenic variant in homozygosity is associated with early disease and a worse prognosis.

Late onset Pompe Disease in India - Beyond the Caucasian phenotype

We evaluated the clinical histories, motor and pulmonary functions, cardiac phenotypes and GAA genotypes of an Indian cohort of twenty patients with late onset Pompe disease (LOPD) in this multi-centre study. A mean age at onset of symptoms and diagnosis of 9.9 ± 9.7 years and 15.8 ± 12.1 years respectively was identified. All patients had lower extremity limb-girdle muscle weakness. Seven required ventilatory support and seven used mobility assists. Of the four who used both assists, two received ventilatory support prior to wheelchair use. Cardiac involvement was seen in eight patients with various combinations of left ventricular hypertrophy, tricuspid regurgitation, cardiomyopathy, dilated ventricles with biventricular dysfunction and aortic regurgitation. Amongst 20 biochemically diagnosed patients (low residual GAA enzyme activity) GAA genotypes of 19 patients identified homozygous variants in eight and compound heterozygous in 11: 27 missense, 3 nonsense, 2 initiator codon, 3 splice site and one deletion. Nine variants in 7 patients were novel. The leaky Caucasian, splice site LOPD variant, c.-32-13T>G mutation was absent. This first study from India provides an insight into a more severe LOPD phenotype with earlier disease onset at 9.9 years compared to 33.3 years in Caucasian patients, and cardiac involvement more than previously reported. The need for improvement in awareness and diagnosis of LOPD in India is highlighted.

Pompe disease: pathogenesis, molecular genetics and diagnosis

Pompe disease (PD) is a rare autosomal recessive disorder caused by mutations in the GAA gene, localized on chromosome 17 and encoding for acid alpha-1,4-glucosidase (GAA). Currently, more than 560 mutations spread throughout GAA gene have been reported. GAA catalyzes the hydrolysis of α-1,4 and α-1,6-glucosidic bonds of glycogen and its deficiency leads to lysosomal storage of glycogen in several tissues, particularly in muscle. PD is a chronic and progressive pathology usually characterized by limb-girdle muscle weakness and respiratory failure. PD is classified as infantile and childhood/adult forms. PD patients exhibit a multisystemic manifestation that depends on age of onset.

Early diagnosis is essential to prevent or reduce the irreversible organ damage associated with PD progression. Here, we make an overview of PD focusing on pathogenesis, clinical phenotypes, molecular genetics, diagnosis, therapies, autophagy and the role of miRNAs as potential biomarkers for PD.

Splice modulating antisense oligonucleotides restore some acid-alpha-glucosidase activity in cells derived from patients with late-onset Pompe disease

Pompe disease is caused by mutations in the GAA gene, resulting in deficient lysosomal acid-α-glucosidase activity in patients, and a progressive decline in mobility and respiratory function. Enzyme replacement therapy is one therapeutic option, but since not all patients respond to this treatment, alternative interventions should be considered. One GAA mutation, c.-32-13T > G, impacts upon normal exon 2 splicing and is found in two-thirds of late-onset cases. We and others have explored a therapeutic strategy using splice modulating phosphorodiamidate morpholino oligomers to enhance GAA exon 2 inclusion in the mature mRNA of patients with one c.-32-13T > G allele. We designed 20 oligomers and treated fibroblasts derived from five patients to identify an oligomer sequence that maximally increased enzyme activity in all fibroblasts. The most effective splice correcting oligomer was chosen to treat forced-myogenic cells, derived from fibroblasts from nine patients carrying the c.-32-13T > G mutation. After transfection, we show increased levels of the full-length GAA transcript, acid-α-glucosidase protein, and enzyme activity in all patients’ myogenic cells, regardless of the nature of the mutation in the other allele. This data encourages the initiation of clinical trials to assess the therapeutic efficacy of this oligomer for those patients carrying the c.-32-13T > G mutation.

Molecular genetics of Pompe disease: a comprehensive overview

Pompe disease (PD) is an autosomal recessive lysosomal disorder caused by the deficient activity of acid alpha-glucosidase (GAA) enzyme due to mutations in the GAA gene. The enzymatic deficiency leads to the accumulation of glycogen within the lysosomes. Clinically, the disease has been classically classified in infantile and childhood/adult forms. The GAA gene has been localized to chromosome 17q25.2-q25.3 and to date, 582 mutations distributed throughout the whole gene have been reported (HGMD: http://www.hgmd.cf.ac.uk/ac/). All types of mutations have been described; missense variants are the most frequent type followed by small deletions. Most GAA mutations are private or found in a small number of families. However, an exception is represented by the c.-32-13T>G splice mutation that is very common in patients of Caucasian origin affected by the childhood/adult form of the disease, with an allelic frequency ranging from 40% to 70%. In this article, we review the spectrum of GAA mutations, their distribution in different populations, and their classification according to their impact on GAA splicing process, protein expression and activity. In addition, whenever possible, we discuss the phenotype/genotype correlation. The information collected in this review provides an overview of the molecular genetics of PD and can be used to facilitate diagnosis and genetic counseling of families affected by this disorder.

Reevaluating the pathogenicity of the mutation c.1194 +5 G>A in GAA gene by functional analysis of RNA in a 61-year-old woman diagnosed with Pompe disease by muscle biopsy

Glycogen storage disease type II, or Pompe disease, is an autosomal recessive disorder caused by deficiency of lysosomal acid alpha-glucosidase (GAA). We performed genetic analysis to confirm the diagnosis of Pompe disease in a 61-year-old patient with progressive weakness in extremities, severe Sleep Apnea-Hypopnea Syndrome, a significant reduction of alpha-glucosidase in liquid sample of peripheral blood and muscular biopsy diagnosis. GAA gene sequencing showed the patient is homozygous for the splice-site mutation c.1194+5G>A, considered as nonpathogenic in Pompe Center mutation database. Further molecular RNA characterization of GAA transcripts allowed us to identify abnormal processing of pre-mRNA, leading to aberrant transcripts and a significant reduction of GAA mRNA levels. Our results indicate that c.1194+5G>A is a pathogenic splice-site mutation and should be considered as such for diagnostic purposes. This study emphasizes the potential role of functional studies to determine the consequences of mutations with no evident pathogenicity.

A molecular analysis of the GAA gene and clinical spectrum in 38 patients with Pompe disease in Japan

Pompe disease is an autosomal recessive disorder caused by acid α-glucosidase (GAA) deficiency, which results in the accumulation of glycogen in lysosomes in multiple tissues, including cardiac, skeletal, and smooth muscle cells. Thus far, 558 sequence variants of the GAA gene have been published in the Pompe Disease Mutation Database, and some mutations appear with considerable frequency in particular ethnic groups, such as Caucasians, Taiwanese, Chinese, and Koreans. However, the GAA mutation pattern in Japanese patients remains poorly understood. We analyzed the relationship between the genetic and clinical features of 38 mostly Japanese patients with Pompe disease from 35 unrelated families. We identified 28 different GAA gene mutations, including 7 novel mutations, by a GAA gene analysis. c.546G > T (22.9%) and c.1857C > G (14.3%) were the most common mutations and accounted for 37.1% of the total mutant alleles. In the six patients with infantile-onset Pompe disease (IOPD), c.1857C > G was also the most common mutation. In addition, there were 13 homozygotes (5 with the c.546G > T) among the 35 families, which is the highest frequency reported thus far. Regarding the initial symptoms, cardiomegaly was the most common (3/6 = 50%) in IOPD patients, while muscle weakness was observed the most frequently in patients with late-onset Pompe disease (LOPD) (15/30 = 50%). Notably, all IOPD patients who showed respiratory distress at the time of onset require respiratory assistance at present (4/4 = 100%). Regarding the presenting symptoms, cardiomegaly (6/6 = 100%) and hepatomegaly (4/6 = 66.7%) were more commonly seen in IOPD, and muscle weakness (24/29 = 82.7%) was observed more frequently in LOPD. Respiratory assistance is required at present in 33.3% of IOPD patients and 50% of LOPD patients, and 20% of IOPD patients and 29.6% of LOPD patients are wheelchair users. These individual clinical courses may be influenced by the timing of the diagnosis and treatment; for example, in 2007, an ERT orphan drug for treatment of Pompe disease, Alglucosidase alfa, was made available in Japan, and there were 5 (5/6 = 83.3%) wheelchair users diagnosed from 2008 to 2009 (cases 32–38) and 4 (4/27 = 14.8%) from 2010 to 2015 (cases 1–31). These findings underscore the importance of the early diagnosis and treatment.

New mutations and genotype-phenotype correlation in late-onset Pompe patients

Pompe disease is a glycogen storage disease caused by acid alfa-glucosidase deficiency. Here, we report clinical properties, genetic features of our late-onset Pompe patients. Seven patients were followed during the last 10 years in our institute. The clinical and laboratory findings were reviewed. Neuropsychological evaluation was performed in four patients. Myotonic discharges of paraspinal muscles and denervation potentials were seen in all patients at the diagnosis and were disappeared during follow-up in two. Only one patient, whose MRI showed cerebral atrophy, had attention and executive dysfunction. Compound heterozygous patients with IVS 1-13T>G have a milder disease. One patient who has homozygous IVS 1-13T>G mutation had more severe disease. Two of our patients who had very severe and fatal disease course carry double mutations on both alleles (c.547-39T>G and c.858+5ins7) that previously scored as "unknown" in Erasmus Pompe Center database. Lastly, we found new mutations (c.1209 C>A, 2737dupG) in two patients carrying IVS 1-13T>G in the other allele. Systemic involvements are very rare in late-onset Pompe patients. Similarly, Pompe disease does not cause cognitive impairment in adult population. Homozygous IVS 1-13T>G mutation and c.547-39T>G mutation which are previously noted as "unknown" pathogenicities cause a more severe disease.

Diagnosis and treatment of late-onset Pompe disease in the Middle East and North Africa region: consensus recommendations from an expert group

Background

Pompe disease is a rare autosomal recessive disorder caused by a deficiency of the lysosomal enzyme alpha-glucosidase responsible for degrading glycogen. Late-onset Pompe disease has a complex multisystem phenotype characterized by a range of symptoms.

Methods

An expert panel from the Middle East and North Africa (MENA) region met to create consensus-based guidelines for the diagnosis and treatment of late-onset Pompe disease for the MENA region, where the relative prevalence of Pompe disease is thought to be high but there is a lack of awareness and diagnostic facilities.

Results

These guidelines set out practical recommendations and include algorithms for the diagnosis and treatment of late-onset Pompe disease. They detail the ideal diagnostic workup, indicate the patients in whom enzyme replacement therapy should be initiated, and provide guidance on appropriate patient monitoring.

Conclusions

These guidelines will serve to increase awareness of the condition, optimize patient diagnosis and treatment, reduce disease burden, and improve patient outcomes.

Capture-based high-coverage NGS: a powerful tool to uncover a wide spectrum of mutation types

PURPOSE

Next-generation sequencing (NGS) has been widely applied to clinical diagnosis. Target-gene capture followed by deep sequencing provides unbiased enrichment of the target sequences, which not only accurately detects single-nucleotide variations (SNVs) and small insertion/deletions (indels) but also provides the opportunity for the identification of exonic copy-number variants (CNVs) and large genomic rearrangements.

METHOD

Capture NGS has the ability to easily detect SNVs and small indels. However, genomic changes involving exonic deletions/duplications and chromosomal rearrangements require more careful analysis of captured NGS data. Misaligned raw sequence reads may be more than just bad data. Some mutations that are difficult to detect are filtered by the preset analytical parameters. "Loose" filtering and alignment conditions were used for thorough analysis of the misaligned NGS reads. Additionally, using an in-house algorithm, NGS coverage depth was thoroughly analyzed to detect CNVs.

RESULTS

Using real examples, this report underscores the importance of the accessibility to raw sequence data and manual review of suspicious sequence regions to avoid false-negative results in the clinical application of NGS. Assessment of the NGS raw data generated by the use of loose filtering parameters identified several sequence aberrations, including large indels and genomic rearrangements. Furthermore, NGS coverage depth analysis identified homozygous and heterozygous deletions involving single or multiple exons.

CONCLUSION

Our results demonstrate the power of deep NGS in the simultaneous detection of point mutations and intragenic exonic deletion in one comprehensive step.Genet Med 18 5, 513-521.

Novel GAA mutations in patients with Pompe disease

Pompe disease is an autosomal recessive disorder linked to GAA gene that leads to a multi-system intralysosomal accumulation of glycogen. Mutation identification in the GAA gene can be very important for early diagnosis, correlation between genotype-phenotype and therapeutic intervention. For this purpose, peripheral blood from 57 individuals susceptible to Pompe disease was collected and all exons of GAA gene were amplified; the sequences and the mutations were analyzed in silico to predict possible impact on the structure and function of the human protein. In this study, 46 individuals presented 33 alterations in the GAA gene sequence, among which five (c.547-67C>G, c.547-39T>G, p.R437H, p.L641V and p.L705P) have not been previously described in the literature. The alterations in the coding region included 15 missense mutations, three nonsense mutations and one deletion. One insertion and other 13 single base changes were found in the non-coding region. The mutation p.G611D was found in homozygosis in a one-year-old child, who presented low levels of GAA activity, hypotonia and hypertrophic cardiomyopathy. Two patients presented the new mutation p.L705P in association with c.-32-13T>G. They had low levels of GAA activity and developed late onset Pompe disease. In our study, we observed alterations in the GAA gene originating from Asians, African-Americans and Caucasians, highlighting the high heterogeneity of the Brazilian population. Considering that Pompe disease studies are not very common in Brazil, this study will help to better understand the potential pathogenic role of each change in the GAA gene. Furthermore, a precise and early molecular analysis improves genetic counseling besides allowing for a more efficient treatment in potential candidates.

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.

Identification of the first deletion-insertion involving the complete structure of GAA gene and part of CCDC40 gene mediated by an Alu element

Pompe disease is an uncommon autosomal recessive glycogen storage disorder caused by deficiency of acid α-glucosidase. Classic infantile form triggers severe cardiomyopathy, hypotonia, and respiratory failure, leading to death within the first two years of life. The majority of patients with Pompe disease have been reported to have point mutations in the GAA gene. We report the first complex deletion-insertion encompassing the complete structure of GAA gene and a large fragment of the gene CCDC40 in a patient with very severe form of Pompe disease. Sequencing analysis of breakpoints allowed us to determine the potential implication of an Alu repeat in the pathogenic mechanism. We suggest that molecular strategy of Pompe disease should include systematic analysis of large rearrangements.

A cross-sectional single-centre study on the spectrum of Pompe disease, German patients: molecular analysis of the GAA gene, manifestation and genotype-phenotype correlations

BACKGROUND

Pompe disease (Glycogen storage disease type II, GSD II, acid alpha-glucosidase deficiency, acid maltase deficiency, OMIM # 232300) is an autosomal-recessive lysosomal storage disorder due to a deficiency of acid alpha-glucosidase (GAA, acid maltase, EC 3.2.1.20, Swiss-Prot P10253). Clinical manifestations are dominated by progressive weakness of skeletal muscle throughout the clinical spectrum. In addition, the classic infantile form is characterised by hypertrophic cardiomyopathy.

METHODS

In a cross-sectional single-centre study we clinically assessed 3 patients with classic infantile Pompe disease and 39 patients with non-classic presentations, measured their acid alpha-glucosidase activities and analysed their GAA genes.

RESULTS

Classic infantile patients had nearly absent residual enzyme activities and a typical clinical course with hypertrophic cardiomyopathy until the beginning of therapy. The disease manifestations in non-classic patients were heterogeneous. There was a broad variability in the decline of locomotive and respiratory function. The age of onset ranged from birth to late adulthood and correlated with enzyme activities. Molecular analysis revealed as many as 33 different mutations, 14 of which are novel. All classic infantile patients had two severe mutations. The most common mutation in the non-classic group was c.-32-13T>G. It was associated with a milder course in this subgroup.

CONCLUSIONS

Disease manifestation strongly correlates with the nature of the GAA mutations, while the variable progression in non-classic Pompe disease is likely to be explained by yet unknown modifying factors. This study provides the first comprehensive dataset on the clinical course and the mutational spectrum of Pompe disease in Germany.

Infantile Pompe disease: clinical and genetic characteristics with an experience of enzyme replacement therapy

Pompe disease is an autosomal recessive disorder caused by lysosomal acid α-glucosidase deficiency. Infantile-onset Pompe disease presents with cardiomyopathy and hypotonia, leading to premature death. This article describes 7 infantile Pompe disease cases and provides their molecular bases and clinical outcomes after enzyme replacement therapy for the first time in Korea. Molecular genetic analyses revealed the presence of 9 different mutations, including 5 novel mutations (c.2171C>A, c.2774C>T, c.1582_3de12, c.1261_1263Tms, and c.1322_1326+9de114). The most common mutation in these 7 patients was c.1316T>A (28%). Four patients received intravenous recombinant human acid α-glucosidase therapy for 2 years, on average, without significant side effects during the treatment course. They all exhibited increased muscle power, with considerable improvement in cardiac function. Pompe disease is heterogeneous regarding both clinical features and molecular characteristics. Early identification of Pompe disease is very important, considering that enzyme replacement therapy is a safe and effective treatment for early-onset patients.

Predicting cross-reactive immunological material (CRIM) status in Pompe disease using GAA mutations: lessons learned from 10 years of clinical laboratory testing experience

Enzyme replacement therapy (ERT) for Pompe disease using recombinant acid alpha-glucosidase (rhGAA) has resulted in increased survival although the clinical response is variable. Cross-reactive immunological material (CRIM)-negative status has been recognized as a poor prognostic factor. CRIM-negative patients make no GAA protein and develop sustained high antibody titers to ERT that render the treatment ineffective. Antibody titers are generally low for the majority of CRIM-positive patients and there is typically a better clinical outcome. Because immunomodulation has been found to be most effective in CRIM-negative patients prior to, or shortly after, initiation of ERT, knowledge of CRIM status is important before ERT is begun. We have analyzed 243 patients with infantile Pompe disease using a Western blot method for determining CRIM status and using cultured skin fibroblasts. Sixty-one out of 243 (25.1%) patients tested from various ethnic backgrounds were found to be CRIM-negative. We then correlated the CRIM results with GAA gene mutations where available (52 CRIM-negative and 88 CRIM-positive patients). We found that, in most cases, CRIM status can be predicted from GAA mutations, potentially circumventing the need for invasive skin biopsy and time wasted in culturing cells in the future. Continued studies in this area will help to increase the power of GAA gene mutations in predicting CRIM status as well as possibly identifying CRIM-positive patients who are at risk for developing high antibody titers.

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.

Long-term follow-up results in enzyme replacement therapy for Pompe disease: a case report

Pompe disease (PD) is a metabolic myopathy caused by a deficiency of acid-alpha glucosidase (GAA), a lysosomal enzyme that cleaves glycogen. The classic infantile-onset form is characterised by severe hypotonia and cardiomyopathy. Untreated patients usually die within the first year of life due to cardiorespiratory failure. Several studies involving patients with infantile-onset PD have shown that enzyme replacement therapy (ERT) with alglucosidase alfa, recombinant human GAA (rhGAA), significantly prolongs survival, decreases cardiomegaly, and improves cardiac function and conduction abnormalities. However, the efficacy on motor, cognitive and social milestones appears to be more related to the condition of the patient before the start of treatment. To date, the sample of early diagnosed and treated patients is small and the length of follow-up is still limited. We report the results of a long-term follow-up of one patient presenting severe bradycardia and cardiomyopathy at birth, diagnosed in the third day of life and successfully treated by ERT. Serum muscle enzymes at diagnosis were AST 200 U/L, ALT 99 U/L and CPK 731 U/L (n.v. 0-295); the molecular study identified the homozygous missense mutation c.1933 G> A p.Asp645Asn (GAA exon 14). Left Ventricular Mass Index (LVMI) at baseline was 171 g/m(2) (Z-score = 4.3) and decreased to normal values since the 3-month follow-up. A muscle biopsy performed at 18 months after the start of therapy, showed only a low degree of muscle involvement. To our knowledge, this is the longest ERT treatment follow-up in a symptomatic neonatal patient with Pompe disease.

Chorionic villi ultrastructure in the prenatal diagnosis of glycogenosis type II

OBJECTIVE

To perform the ultrastructural examination of a chorionic villi biopsy as a predictor of foetal involvement in the infantile form of glycogenosis type II (Pompe disease).

METHODS

Ultrastructural, biochemical and genetic analyses were performed on chorionic villi biopsies of three consecutive pregnancies in a woman with a previous child affected by Pompe disease.

RESULTS

In the only affected foetus, glycogen storage was observed in fibrocytes and endothelial cells of a chorionic villi sample at 11 week's gestation. Severe multi-organ involvement was demonstrated in the tissues of the aborted foetus. No abnormal material was found in the chorionic samples of two subsequent pregnancies, and a healthy boy and girl were born at term and remain unaffected. Both exhibited a partial reduction in acid maltase and were carriers of the maternal mutation.

CONCLUSIONS

Ultrastructural findings correlated with biochemical and genetic results, providing a clear and early indicator of the definite diagnosis for future pregnancy management or an early therapeutic approach.

Molecular diagnosis of German patients with late-onset glycogen storage disease type II

In patients with late-onset glycogen storage disease type II, one mutation, c.-32-13T>G, in the α-glucosidase (GAA) gene is identified frequently in European populations from different regions along with many rarer mutations. We have performed molecular genetic investigations in 18 German index patients with late-onset disease. The c.-32-13T>G, c.525delT (p.Glu176fsX45), and c.2481+102_2646+31del mutations were detected by PCR/restriction enzyme digest. Other mutations were detected by sequencing. All patients were compound heterozygous and 17 patients harboured the c.-32-13T>G mutation. Seven other previously described mutations (including the c.-32-13T>G) were identified, of which the p.C103G (c.307T>G) and the c.2481+102_2646+31del mutations were present each in three unrelated patients. Sequencing revealed five novel mutations.

CONCLUSIONS

Genetic testing was able to identify the genetic defects in all patients and screening of the c.-32-13T>G mutation identified 94% of the cases. This is important for quick and reliable diagnosis, especially in view of enzyme replacement. Among the rarer mutations, c.2481+102_2646+31del and p.C103G are rather frequent in Germany.