Pseudodeficiency Allele Research Articles

Newborn screening for Pompe disease in Japan: report and literature review of mutations in the GAA gene in Japanese and Asian patients.

A newborn screening program for Pompe disease using dried blood spots (DBSs) was initiated in Japan. Here, we summarized this screening program and described the results of the GAA gene analysis. From April 2013 to November 2016, 103,204 newborns were screened; 71 had low acid alpha-glucosidase (AαGlu) activity. GAA sequencing showed that 32 (45.1%) and 37 (52.1%) of these newborns were homozygous and heterozygous for pseudodeficiency alleles c.[1726G>A; 2965G>A], respectively. Moreover, 24 of 32 newborns with homozygous c.[1726G>A; 2965G>A] alleles had no mutations, and the other eight had one mutation each. Thirty-five of 37 newborns with heterozygous c.[1726G>A; 2965G>A] alleles had one mutation, and the other two had two mutations each. Only one newborn who had two mutations did not harbor c.[1726G>A; 2965G>A] alleles. Thus, it was difficult to distinguish newborns with c.[1726G>A; 2965G>A] alleles from newborns with pre-symptomatic Pompe disease using AαGlu assays in DBSs or fibroblasts; GAA gene sequencing was necessary. Seventy-one newborns had 50 variants, including 21 mutations or predictably pathogenic variants, and 29 polymorphisms or predictably non-pathogenic variants. Four of 21 mutations or predictably pathogenic variants and four of 29 polymorphisms or predictably non-pathogenic variants were novel. No infantile-onset Pompe disease was detected, and three newborns were diagnosed with potential late-onset Pompe disease. In the literature, 156 variants have been reported for 296 patients from 277 families in 41 articles from Japan, Korea, Taiwan, and China. Our results provide insights into GAA gene mutation profiles and the relationship between GAA and Pompe disease in Asian populations.

Exon Sequencing for the Presence of Late Onset Tay‐Sachs

Tay‐Sachs is a disease that causes rapid developmental stagnation and death in infants. It primarily affects people of French Canadian, Cajun, and Ashkenazi Jewish descent. In recent years an alternate form of the disease, called late onset Tay‐Sachs (LOTS), has been described. LOTS is caused by the inheritance of one null allele and a pseudodeficiency allele of the hexosaminidase A (HEXA) gene. The mutation rate of the pseudodeficiency is not well known. The aim of this experiment was to examine the DNA of the descendants of an Ashkenazi Jewish individual who was believed to have undiagnosed LOTS. The purpose of this case study is to attempt to confirm this suspected diagnosis by identifying potential mutations in the family members. DNA of the HEXA gene from three family members of the suspected LOTS patient (wife and 2 daughters) and one control set (unrelated female) was sequenced. The sequences were aligned and compared both by hand and using the NCBI Blast database and the Benchling tool. No known mutations or confirmed novel mutations have been found in all fourteen exons sequenced. Currently re‐sequencing of some regions that showed potential single nucleotide polymorphisms (SNPs) as well as sequencing the promoter region of the gene is underway. If a mutation is confirmed this research could help pave the way for further genetic testing in the broader population in order to fully grasp the prevalence of LOTS pseudodeficiency alleles within the Ashkenazi population.Support or Funding InformationHamline Undergraduate Collaborative ResearchRidgeway Forum FundThis abstract is from the Experimental Biology 2018 Meeting. There is no full text article associated with this abstract published in The FASEB Journal.

P.214 - Interim analysis of an investigator-initiated multi-site late-onset Pompe disease screening study

Late-onset Pompe disease (LOPD) is an inherited lysosomal storage disease, in which the enzyme acid alpha-glucosidase (GAA) is deficient. It is characterized by proximal limb-girdle muscle weakness and respiratory insufficiency. The disease is progressive, and if left untreated, may result in significant motor disability and respiratory failure. As of 2010, nine studies have been published documenting the incidence of LOPD. In the U.S. the incidence of the disease is 1 in 40,000. Recently Pompe disease has become part of the newborn screening panel in multiple states. Due to the relatively high frequency of Pompe disease reported, we would expect that large medical centers specializing in neuromuscular diseases would see a higher incidence of LOPD among their patients than what is currently reported. The objective of this multi-site investigator-initiated study is to determine true prevalence of LOPD in patients presenting to academic tertiary geographically disparate neuromuscular centers in the US and Canada using specific selection criteria. Clinic patients who present with symptoms of undiagnosed proximal muscle weakness, neck weakness or elevation of creatinine kinase, are screened for LOPD. Total recruitment goal is 1,500 subjects across 14 sites. Since study initiation we have enrolled 465 subjects. 42/465 (9.0%) had abnormal GAA enzyme levels (<10 pmol/punch/hr). 5/465 (1.1%) were diagnosed, confirmed by gene sequencing, with LOPD. 6/465 (1.3%) were carriers of one GAA gene mutation, 3/465 (0.6%) had one GAA variant of uncertain significance, and 3/465 (0.6%) had the pseudodeficiency allele. The study is ongoing however behind schedule. The feasibility of enrolling 1500 subjects in an investigator-initiated study has proven to be more challenging than anticipated.

Enzyme activities of α-glucosidase in Japanese neonates with pseudodeficiency alleles

Lysosomal storage disorders (LSDs) are caused by defective enzyme activities in lysosomes, characterized by the accumulation of sphingolipids, glycolipids, oligosaccharides, mucopolysaccharides, the oxidation products of cholesterol, and other biological substances. A growing number of clinical studies have suggested the enhanced efficacy of existing therapies, including enzyme replacement therapy, which is effective when it is initiated during the presymptomatic period. Thus, the identification of disease-affected individuals by newborn screening has been considered an effective platform. Previous studies have suggested that the discrimination of infantile-onset Pompe disease (IOPD) requires multi-step examination of GAA enzyme activity using the fluorometric technique. In sharp contrast, the MS/MS-based technique can identify the population of IOPD and the pseudodeficiency alleles of the GAA enzyme [Liao HC et al. Clin Chem (2017) in press; doi: http://dx.doi.org/10.1373/clinchem.2016.269027]. To determine whether MS/MS-based assay can identify these two populations in Japanese neonates, we first performed a validation study of this assay using flow-injection analysis (FIA)-MS/MS and liquid chromatography (LC)-MS/MS followed by examination of GAA enzyme activity in our population. By minimizing the effect of substrate-derived in-source decomposition products, the activities of 6 LSD enzymes were quantified in FIA-MS/MS and LC-MS/MS. The mean value of GAA activity with IOPD, pseudodeficiency alleles, and healthy controls by FIA-MS/MS were 1.0±0.3μmol/h/L (max, 1.3; min, 0.7; median, 1.2; n=3), 2.7±0.7μmol/h/L (max, 4.5; min, 1.5; median, 2.5; n=19), and 12.9±5.4μmol/h/L (max, 29.6; min, 2.5; median, 11.0; n=83), respectively. These results suggest that the population of GAA with pseudodeficiency alleles has approximately 20% of GAA enzyme activity compared to controls, providing the preliminary evidence to estimate the cut-off values in the Japanese population using this technique.

Mass Spectrometry but Not Fluorimetry Distinguishes Affected and Pseudodeficiency Patients in Newborn Screening for Pompe Disease.

Deficiency of the lysosomal enzyme acid α-glucosidase (GAA) causes Pompe disease. Newborn screening for Pompe disease is ongoing, and improved methods for distinguishing affected patients from those with pseudodeficiency, especially in the Asian population, would substantially reduce the number of patient referrals for clinical follow-up. We measured the enzymatic activity of GAA in dried blood spots on newborn screening cards (DBS) using a tandem mass spectrometry (MS/MS) assay. The assay displayed a relatively large analytical range compared to the fluorimetric assay with 4-methylumbelliferyl-α-glucoside. DBS from newborns confirmed to have infantile-onset Pompe disease (IOPD, n = 11) or late-onset Pompe disease (LOPD) (n = 12) and those from patients bearing pseudodeficiency alleles with or without Pompe mutations, or Pompe disease carriers (n = 230) were studied. With use of the MS/MS GAA assay in DBS, 96% of the pseudodeficiency newborns and all of the Pompe disease carriers were well separated from the IOPD and LOPD newborns. The fluorimetric assay separated <10% of the pseudodeficiencies from the IOPD/LOPD group. The relatively large analytical range MS/MS GAA assay but not the fluorimetric assay in DBS provides a robust approach to reduce the number of referrals and should dramatically facilitate newborn screening of Pompe disease.

Targeted population screening of late onset Pompe disease in unspecified myopathy patients for Korean population

We performed targeted population screening of late onset Pompe disease (LOPD) in unspecified myopathy patients, because early diagnosis is difficult due to its heterogeneous clinical features. We prospectively enrolled 90 unrelated myopathic patients who had one or more signs out of five LOPD-like clinical findings (proximal weakness, axial weakness, lingual weakness, respiratory difficulty, idiopathic hyperCKemia). Acid alpha glucosidase activity was evaluated with dried blood spot and mixed leukocyte simultaneously. For a final diagnosis of LOPD, 16 patients with decreased enzyme activity were genotyped by GAA molecular analysis. We found two patients with LOPD (2.2%), and the remaining 14 patients had at least one G576S or E689K mutation, known as the pseudodeficiency allele. Acid alpha glucosidase activity of LOPD patients was significantly lower than that of patients with at least one pseudodeficiency allele (p = 0.017). This study is the first LOPD screening study for targeted Korean population, and more generally, an Asian population. Our findings suggest that for diagnosis of LOPD in Asian population, modified cutoff value of acid alpha glucosidase activity with dry blood spot considering that of patients having heterozygote pathogenic variants or pseudodeficiency alleles may reduce time and cost requirements and increase the comfort of patients.

Research Article Pseudo deficiency of acid α-glucosidase: a challenge in the newborn screening for Pompe diseases

When a low activity of acid α-glucosidase (GAA) is found, particularly in newborn screening programs, to differentiate α-glucosidase pseudo deficiency from true Pompe disease is important and urgent, as the result generates parental stress and also because this differentiation drives decisions related to the management of the case. Here, we report a case of GAA pseudo deficiency detected in a newborn screening performed by a private laboratory in Brazil. The confirmatory laboratory investigation performed at our service showed reduction of GAA activity on the dried blood spot, with inconclusive results when GAA activity was assayed in leukocytes. Genotyping of the GAA gene with next-generation sequencing revealed the common pathogenic mutation c.-32-13T>G and the “pseudo deficiency allele” p. [Gly576Ser; Glu689Lys], each one in heterozygous state and in trans. This report illustrates the need of newborn screening programs to have the adequate support to perform a comprehensive investigation whenever an abnormality is found in the initial screening test

Determination of frequencies of alleles, associated with the pseudodeficiency of lysosomal hydrolases, in population of Ukraine.

The pseudodeficiency of lysosomal hydrolases described as a significant reduction in enzyme activi­ty in vitro in clinically healthy individuals, can lead to diagnostic errors in the process of biochemical analysis of lysosomal storage disease in case of its combination with pathology of another origin. Pseudodeficiency is mostly caused by some non-pathogenic changes in the corresponding gene. These changes lead to the in vitro lability of the enzyme molecule, whereas in vivo the enzyme retains its functional activity. To assess the prevalence of the most common lysosomal hydrolases pseudodeficiency alleles in Ukraine, we have determined the frequency of alleles c.1055A>G and c.* 96A>G in the ARSA gene, substitutions c.739C>T (R247W) and c.745C>T (R249W) in the HEXA gene, c.1726G>A (G576S) and c.2065G>A (E689K) in the GAA gene, c.937G>T (D313Y) in the GLA1 gene and c.898G>A (A300T) in the IDUA gene in a group of 117 healthy individuals from different regions of the country and 14 heterozygous carriers of pathogenic mutations in the HEXA gene (parents of children with confirmed diagnosis of Tay-Sachs disease). The total frequency of haplotypes, associated with arylsulfatase A pseudodeficiency, in healthy people in Ukraine (c.1055G/c.*96G and c.1055G/c.*96A haplotypes) was 10.3%. The frequency of c.739C>T (R247W) allele, associated with hexo­saminidase A pseudodeficiency, among Tay-Sachs carriers from Ukraine was 7.1%. The total frequency of α-glucosidase pseudodeficiency haplotypes in healthy individuals in Ukraine (c.1726A/c.2065A and c.1726G/c.2065A haplotypes) was 2.6%. No person among examined individuals with the substitution c.937G>T (D313Y) in the GLA1 gene and c.898G>A (A300T) in the IDUA gene was found. The differential diagnostics of lysosomal storage diseases requires obligatory determination of the presence of the pseudodeficiency alleles, particularly the ones with high incidence in the total population. Ignoring phenomenon of pseudodeficiency may lead to serious diagnostic errors.

Sulfatide Analysis by Mass Spectrometry for Screening of Metachromatic Leukodystrophy in Dried Blood and Urine Samples.

Metachromatic leukodystrophy (MLD) is an autosomal recessive disorder caused by deficiency in arylsulfatase A activity, leading to accumulation of sulfatide substrates. Diagnostic and monitoring procedures include demonstration of reduced arylsulfatase A activity in peripheral blood leukocytes or detection of sulfatides in urine. However, the development of a screening test is challenging because of instability of the enzyme in dried blood spots (DBS), the widespread occurrence of pseudodeficiency alleles, and the lack of available urine samples from newborn screening programs. We measured individual sulfatide profiles in DBS and dried urine spots (DUS) from MLD patients with LC-MS/MS to identify markers with the discriminatory power to differentiate affected individuals from controls. We also developed a method for converting all sulfatide molecular species into a single species, allowing quantification in positive-ion mode upon derivatization. In DBS from MLD patients, we found up to 23.2-fold and 5.1-fold differences in total sulfatide concentrations for early- and late-onset MLD, respectively, compared with controls and pseudodeficiencies. Corresponding DUS revealed up to 164-fold and 78-fold differences for early- and late-onset MLD patient samples compared with controls. The use of sulfatides converted to a single species simplified the analysis and increased detection sensitivity in positive-ion mode, providing a second option for sulfatide analysis. This study of sulfatides in DBS and DUS suggests the feasibility of the mass spectrometry method for newborn screening of MLD and sets the stage for a larger-scale newborn screening pilot study.

AB067. Glucose tetrasaccharide (Glc4) level in urine sample as a biomarker for Pompe patients.

Pompe disease is a lysosomal storage disease caused by an accumulation of glycogen in the lysosome due to deficiency of the lysosomal acid alpha-glucosidase (GAA) enzyme. Our team has started newborn screening of Pompe disease since 2008. Until now, around 800,000 newborns have been screening. Rapid diagnostic criteria for the newborns with infantile-onset Pompe disease (IOPD) has been established by our team. Through this effective program, IOPD infants can receive their first ERT within 4 hours of admission and at an average of 11.56±3.4 days of age. However, for late onset Pompe disease (LOPD) newborns, it is very difficult to distinguish them from the newborns with low GAA enzyme activity caused pseudo-deficiency allele (G576S) by clinical manifestations or enzyme activity. Therefore, we try to find a reliable biomarker to distinguish LOPD newborns from pseudo-deficiency. In this study, we analyzed urinary Glc4 levels of the newborns who have pseudo-deficiency (G576S), suspected LOPD (suspected by their genotypes), or IOPD. We found that all the pseudo-deficiency newborns and suspected LOPD newborns had normal urinary Glc4 level, while IOPD had very high urinary Glc4 level before they got ERT. The urinary Glc4 level decreased rapidly after ERT in these IOPD newborns. For long-term ERT follow up, the urinary Glc4 level elevated gradually after longer-term follow-up in some patients, especially in who received ERT later. We also found that urinary Glc4 level was correlated with serum creatine kinase (CK) level in our patients. Our data suggested that urinary Glc4 level is a good biomarker for IOPD newborns, but not LOPD, especially for the pre-symptomatic LOPD patients.

Newborn screening for Fabry disease: Is the A143T allele a pathogenic mutation or a pseudodeficiency allele?

Newborn screening for Fabry disease: Is the A143T allele a pathogenic mutation or a pseudodeficiency allele?

Sixteen novel mutations in the arylsulfatase A gene causing metachromatic leukodystrophy

Metachromatic leukodystrophy (MLD) is a lysosomal storage disorder caused mainly by mutations in the arylsulfatase A (ARSA) gene. In this manuscript we report sixteen novel mutations identified in the ARSA gene of fifteen unrelated patients affected with MLD. Of these 16 mutations nine were missense mutations (p.L11Q, p.S44P, p.L81P, p.R84L, p.V177D, p.P284S, p.R288S, p.G301R, p.P425S), three were nonsense mutations (p.Q51X, p.Y149X, p.C156X), three were frame shift mutations (c.28delG, c.105C>A+106_124dup, c.189delC) and one was a splice-site mutation (c.1102-2A>G). In addition, three previously reported mutations were identified on an allelic background different from the one in the original reports. Two mutations, p.G309S and p.E312D, were identified on the background of the so-called pseudodeficiency (Pd) allele while previously they were reported alone. On the other hand, mutation p.R311X was identified in two unrelated patients not in cis with the Pd mutations, as previously reported.

Newborn screening for Pompe disease in Japan

Pompe disease is caused by a deficiency of acid alpha-glucosidase (GAA) that results in glycogen accumulation, primarily in muscle. Newborn screening (NBS) for Pompe disease has been initiated in Taiwan and is reportedly successful. However, the comparatively high frequency of pseudodeficiency allele makes NBS for Pompe disease complicated in Taiwan. To investigate the feasibility of NBS for Pompe disease in Japan, we obtained dried blood spots (DBSs) from 496 healthy Japanese controls, 29 Japanese patients with Pompe disease, and five obligate carriers, and assayed GAA activity under the following conditions: (1) total GAA measured at pH 3.8, (2) GAA measured at pH 3.8 in the presence of acarbose, and (3) neutral glucosidase activity (NAG) measured at pH 7.0 without acarbose. The % inhibition and NAG/GAA ratio were calculated. For screening, samples with GAA<8% of the normal mean, % inhibition>60%, and NAG/GAA ratio>30 were considered to be positive. Two false positive cases (0.3%) were found, one was a healthy homozygote of pseudodeficiency allele (c.1726G>A). The low false-positive rate suggests that NBS for Pompe disease is feasible in Japan.

Application of enzyme assay and gene analysis in the prenatal diagnosis for a family with glycogen storage disease type II

To carry out prenatal diagnosis for a glycogen storage disease type II (GSD II ) affected family. The acid-α -glucosidase (GAA) activity was measured in whole leukocytes and cultured amniocytes with 4-methylumbelliferyl-α -D-glucopyranoside as substrate and with acarbose as inhibitor. The coding regions of GAA gene were amplified by polymerase chain reaction and analyzed by direct DNA sequencing. The proband and the fetus had low GAA activity (12.3% and 1.1% of the average normal range, respectively). Mutation analysis of the GAA gene revealed a novel nonsense mutation p.W738X and a reported nonsense mutation p.E888X in both the proband and the fetus; the reported pseudodeficiency allele c.[1726G to A: 2065G to A] was found in the proband, the mother and the fetus. The proband and the fetus were both GSD II affected. A combination of GAA activity analysis and mutation analysis is efficient for the prenatal diagnosis of GSD II. Mutation analysis should be a routine method in the prenatal diagnosis of GSD II in Asian population, where pseudodeficiency allele can cause low GAA activity in normal individuals which is relatively common in Asian.

Molecular and structural analysis of metachromatic leukodystrophy patients in Indian population

Metachromatic leukodystrophy (MLD) is an autosomal recessive disorder caused by mutations in arylsulfatase A ( ARSA) gene. No work on molecular genetics of MLD has been reported from India and the mutational spectrum in Indian patients is not known. The present study was undertaken to identify mutations in arylsulfatase A gene in Indian MLD patients, to evaluate genotype–phenotype correlation, and to see the effect of the novel mutants on the protein. Twenty MLD patients (16 families) were screened by ARMS PCR for the most common mutation (c.459+1G>A). Pseudodeficiency alleles were tested by RFLP method whereas rare and novel mutations were scanned by Conformation Sensitive Gel Electrophoresis (CSGE), followed by sequencing. The genotype–phenotype correlation was also attempted. Protein homology modeling analysis was carried out for two novel missense mutations identified, to assess the effect of these mutations on the protein conformation. Nine pathogenic alleles were found in 13 patients (65%). Four previously reported mutations and five novel variants were identified. Five patients (35%) were found to have pseudodeficiency alleles, c.1049A>G (p.Asn350Ser) and c.1524+95A>G. Genotype–phenotype correlation was found to be difficult to establish. Protein modeling studies showed that the mutations cause loss of interactions leading to conformational change in ASA protein. The study identified the mutational spectrum of Indian MLD patients, which will be helpful in genetic counseling, carrier detection and establishing prenatal diagnosis. Homology modeling helped to study conformational change in protein and has implications in generating novel therapeutic molecules.

Frequency of Fabry disease in male and female haemodialysis patients in Spain

BackgroundFabry disease (FD), an X-linked lysosomal storage disorder, is caused by a reduced activity of the lysosomal enzyme α-galactosidase A. The disorder ultimately leads to organ damage (including renal failure) in males and females. However, heterozygous females usually present a milder phenotype with a later onset and a slower progression.MethodsA combined enzymatic and genetic strategy was used, measuring the activity of α-galactosidase A and genotyping the α-galactosidase A gene (GLA) in dried blood samples (DBS) of 911 patients undergoing haemodialysis in centers across Spain.ResultsGLA alterations were found in seven unrelated patients (4 males and 3 females). Two novel mutations (p.Gly346AlafsX347 and p.Val199GlyfsX203) were identified as well as a previously described mutation, R118C. The R118C mutation was present in 60% of unrelated patients with GLA causal mutations. The D313Y alteration, considered by some authors as a pseudo-deficiency allele, was also found in two out of seven patients.ConclusionsExcluding the controversial D313Y alteration, FD presents a frequency of one in 182 individuals (0.55%) within this population of males and females undergoing haemodialysis. Moreover, our findings suggest that a number of patients with unexplained and atypical symptoms of renal disease may have FD. Screening programmes for FD in populations of individuals presenting severe kidney dysfunction, cardiac alterations or cerebrovascular disease may lead to the diagnosis of FD in those patients, the study of their families and eventually the implementation of a specific therapy.

Improving Accuracy of Tay Sachs Carrier Screening of the Non-Jewish Population: Analysis of 34 Carriers and Six Late-Onset Patients With HEXA Enzyme and DNA Sequence Analysis

The purpose of this study was to determine whether combining different testing modalities namely beta-hexosaminidase A (HEXA) enzyme analysis, HEXA DNA common mutation assay, and HEXA gene sequencing could improve the sensitivity for carrier detection in non-Ashkenazi (AJ) individuals. We performed a HEXA gene sequencing assay, a HEXA DNA common mutation assay, and a HEXA enzyme assay on 34 self-reported Tay-Sachs disease (TSD) carriers, six late-onset patients with TSD, and one pseudodeficiency allele carrier. Sensitivity of TSD carrier detection was 91% for gene sequencing compared with 91% for the enzyme assay and 52% for the DNA mutation assay. Gene sequencing combined with enzyme testing had the highest sensitivity (100%) for carrier detection. Gene sequencing detected four novel mutations, three of which are predicted to be disease causing [118.delT, 965A-->T (D322V), and 775A-->G (T259A)]. Gene sequencing is useful in identifying rare mutations in patients with TSD and their families, in evaluating spouses of known carriers for TSD who have indeterminate enzyme analysis and negative for common mutation analysis, and in resolving ambiguous enzyme testing results.

Genetic heterozygosity and pseudodeficiency in the Pompe disease newborn screening pilot program

Pompe disease is an autosomal recessive lysosomal storage disorder (LSD) caused by deficiency of lysosomal acid α-glucosidase (GAA) activity. This is the first LSD in which newborn screening has been shown to improve clinical outcomes. Newborn screening also identified multiple rare gene variants in this population. Among 132,538 newborns screened, 107 babies (1 in 1239) who had low dried blood spot GAA activity were genotyped. Sixty-nine (64.5%) babies had a total of 54 mutations and 35 novel predictably pathogenic mutations; 36 babies (33.6%) who had no mutation were homozygous for the c.[1726A; 2065A] pseudodeficiency allele. Because 81% of the chromosomes (14% in the controls) were in haplotype ∗03, we found a link between the pseudodeficiency allele and other mutated alleles. The newborns with Pompe disease detected by screening had lymphocyte GAA activities 0.45 to 1.65 nmol/mg/h (normal 66.7 ± 33.8), while only 2 of the 100 false-positive cases had GAA activity less than 2.00 nmol/mg/h (or 3% of the normal mean). Therefore, newborn screening for Pompe disease could be successfully conducted by including genotyping and lymphocyte GAA assay, even in a population with mutation heterozygosity and pseudodeficiency.

Mutations and polymorphisms in GUSB gene in mucopolysaccharidosis VII (Sly Syndrome)

Mucopolysaccharidosis VII (MPS VII; Sly syndrome) is an autosomal recessive disorder caused by a deficiency of beta-glucuronidase (GUS, EC 3.2.1.31; GUSB). GUS is required to degrade glycosaminoglycans (GAGs), including heparan sulfate (HS), dermatan sulfate (DS), and chondroitin-4,6-sulfate (CS). Accumulation of undegraded GAGs in lysosomes of affected tissues leads to mental retardation, short stature, hepatosplenomegaly, bone dysplasia, and hydrops fetalis. We summarize information on the 49 unique, disease-causing mutations determined so far in the GUS gene, including nine novel mutations (eight missense and one splice-site). This heterogeneity in GUS gene mutations contributes to the extensive clinical variability among patients with MPS VII. One pseudodeficiency allele, one polymorphism causing an amino acid change, and one silent variant in the coding region are also described. Among the 103 analyzed mutant alleles, missense mutations accounted for 78.6%; nonsense mutations, 12.6%; deletions, 5.8%; and splice-site mutations, 2.9%. Transitional mutations at CpG dinucleotides made up 40.8% of all the described mutations. The five most frequent mutations (accounting for 44/103 alleles) were exonic point mutations, p.L176F, p.R357X, p.P408S, p.P415L, and p.A619 V. Genotype/phenotype correlation was attempted by correlating the effects of certain missense mutations or enzyme activity and stability within phenotypes. These were in turn correlated with the location of the mutation in the tertiary structure of GUS. A total of seven murine, one feline, and one canine model of MPS VII have been characterized for phenotype and genotype.

79. Pseudo-deficiency allele of the N-acetylgalactosamine-4-sulfatase gene identified in a family with Maroteaux–Lamy syndrome (mucopolysaccharidosis type VI)

79. Pseudo-deficiency allele of the N-acetylgalactosamine-4-sulfatase gene identified in a family with Maroteaux–Lamy syndrome (mucopolysaccharidosis type VI)