Determining mutations in G6PC and SLC37A4 genes in a sample of Brazilian patients with glycogen storage disease types Ia and Ib

Glycogen storage disease (GSD) comprises a group of autosomal recessive disorders characterized by deficiency of the enzymes that regulate the synthesis or degradation of glycogen. Types Ia and Ib are the most prevalent; while the former is caused by deficiency of glucose-6-phosphatase (G6Pase), the latter is associated with impaired glucose-6-phosphate transporter, where the catalytic unit of G6Pase is located. Over 85 mutations have been reported since the cloning of G6PC and SLC37A4 genes. In this study, twelve unrelated patients with clinical symptoms suggestive of GSDIa and Ib were investigated by using genetic sequencing of G6PC and SLC37A4 genes, being three confirmed as having GSD Ia, and two with GSD Ib. In seven of these patients no mutations were detected in any of the genes. Five changes were detected in G6PC, including three known point mutations (p.G68R, p.R83C and p.Q347X) and two neutral mutations (c.432G > A and c.1176T > C). Four changes were found in SLC37A4: a known point mutation (p.G149E), a novel frameshift insertion (c.1338_1339insT), and two neutral mutations (c.1287G > A and c.1076-28C > T). The frequency of mutations in our population was similar to that observed in the literature, in which the mutation p.R83C is also the most frequent one. Analysis of both genes should be considered in the investigation of this condition. An alternative explanation to the negative results in this molecular study is the possibility of a misdiagnosis. Even with a careful evaluation based on laboratory and clinical findings, overlap with other types of GSD is possible, and further molecular studies should be indicated.     

Molecular analysis of glycogen storage disease type Ia in Iranian Azeri Turks: identification of a novel mutation

Glycogen storage diseases (GSDs) are caused by abnormalities in enzymes that are involved in the regulation of gluconeogenesis and glycogenolysis. GSD I, an autosomal recessive metabolic disorder, is the most common GSD and has four subtypes. Here, we examined GSD Ia caused by the defective glucose-6-phosphatase catalytic (G6PC) gene. We investigated the frequency of GSD Ia and clarified its molecular aspect in patients with the main clinical and biochemical characteristics of GSD, including 37 unrelated patients with a mean age of three years at the time of diagnosis. All patients belonged to the Azeri Turkish population. Hypoglycaemia and hypertriglyceridaemia were the most frequent laboratory findings. Mutations were detected by performing direct sequencing. Mutation analysis of the G6PC gene revealed that GSD Ia accounted for 11% in GSD patients with involvement of liver. Three patients were homozygous for R83C mutation. In addition, a novel stop mutation, Y85X, was identified in a patient with the typical features of GSD Ia.     

A novel type heterozygous mutation in the glucose-6-phosphatase gene in a Chinese patient with glycogen storage disease Ia

Mutations in the glucose-6-phosphatase (G6Pase) gene are responsible for glycogen storage disease type Ia (GSD Ia). By genotype analysis of the affected pedigree, we identified a novel type mutation in a Chinese patient with GSD Ia. Mutation analysis was performed for the coding region of G6Pase gene using DNA sequencing and TaqMan gene expression assay was used to further confirm the novel mutation. The proband was compound heterozygous for c.311A > T/c.648G > T. Our report expands the spectrum of G6Pase gene mutation in China.     

Distribution of mutations of acid β-D-glucosidase Gene (GBA) among 68 Russian patients with Gaucher’s disease

Gaucher disease (GD) is the most frequent lysosomal storage disease presenting in all populations. Mutations in the acid β-D-glucosidase gene (GBA) cause development of GD, resulting in a decrease or full loss of activity of this enzyme. We report here the results of the molecular-genetic analysis in 68 Russian GD patients from 65 families with the three types of this disease. The GD genotype has been completely elucidated in 58 patients and in all patients we have found at least one mutant allele (92.6%). Besides frequent mutations (p.N370S, c.1263_1317del (del55), p.L444P, p.R463C, Rec NciI) we have identified rare mutations p.R120W, p.R170C, p.R184W, p.G202R, Rec C (p.R120W; p.W184R; p.N188K; p.V191G; p.S196P; p.G202R; p.F213I), presenting in other populations of GD patients. The mutations p.P236T, p.L249Q, p.L288P, p.P319S, p.V352M, p.W381X, p.A384D identified in this study had not been described before. The GBA mutations identified in Russian patients have been compared with those found in patients of other European countries. Genotype-phenotype correlations in GD are discussed.     

Molecular genetic assay of mucopolysaccharidosis IVA in South China

Mucopolysaccharidosis IVA (MPS IVA) is an autosomal recessive lysosomal storage disorder caused by the deficiency of N-acetylgalactosamine-6-sulfate sulfatase (GALNS). Molecular mutational analysis was performed by PCR product sequencing for fourteen exons and exon–intron boundaries of GALNS gene in 21 patients from 19 unrelated families with severe MPS IVA in South China. We identified fifteen different mutations, including 10 reported mutations (p.P125L, p.G290S, p.M318R, p.G340D, p.L366P, p.R386C, p.A392V, c.1243-1G>C, p.L440RfsX54 and p.X523E) and five novel mutations (p.N177S, p.G290R, p.F306S, p.W403_T404delinsCS, p.W520X). All five novel mutations were inherited from parents of the patients and not found in 100 normal control alleles. Three mutations, p.M318R, p.L366P and p.R386C were common, accounting for 36.8% of mutant alleles investigated. One patient homozygous of p.A392V and the other two unrelated patients homozygous of p.L366P presented classical disease course. The results show that the GALNS gene has a different mutational spectrum in South China as compared to other regions. The p.A392V and p.L366P mutations were associated with severe phenotype of MPS IVA.     

Identification of novel mutations in HEXA gene in children affected with Tay Sachs disease from India

Tay Sachs disease (TSD) is a neurodegenerative disorder due to β-hexosaminidase A deficiency caused by mutations in the HEXA gene. The mutations leading to Tay Sachs disease in India are yet unknown. We aimed to determine mutations leading to TSD in India by complete sequencing of the HEXA gene. The clinical inclusion criteria included neuroregression, seizures, exaggerated startle reflex, macrocephaly, cherry red spot on fundus examination and spasticity. Neuroimaging criteria included thalamic hyperdensities on CT scan/T1W images of MRI of the brain. Biochemical criteria included deficiency of hexosaminidase A (less than 2% of total hexosaminidase activity for infantile patients). Total leukocyte hexosaminidase activity was assayed by 4-methylumbelliferyl-N-acetyl-β-D-glucosamine lysis and hexosaminidase A activity was assayed by heat inactivation method and 4-methylumbelliferyl-N-acetyl-β-D-glucosamine-6-sulphate lysis method. The exons and exon-intron boundaries of the HEXA gene were bidirectionally sequenced using an automated sequencer. Mutations were confirmed in parents and looked up in public databases. In silico analysis for mutations was carried out using SIFT, Polyphen2, MutationT@ster and Accelrys Discovery Studio softwares. Fifteen families were included in the study. We identified six novel missense mutations, c.340 G>A (p.E114K), c.964 G>A (p.D322N), c.964 G>T (p.D322Y), c.1178C>G (p.R393P) and c.1385A>T (p.E462V), c.1432 G>A (p.G478R) and two previously reported mutations. c.1277_1278insTATC and c.508C>T (p.R170W). The mutation p.E462V was found in six unrelated families from Gujarat indicating a founder effect. A previously known splice site mutation c.805+1 G>C and another intronic mutation c.672+30 T>G of unknown significance were also identified. Mutations could not be identified in one family. We conclude that TSD patients from Gujarat should be screened for the common mutation p.E462V.     

Misdiagnosis as steatohepatitis in a family with mild glycogen storage disease type 1a

The manifestations of glycogen storage disease type 1a (GSD 1a) are usually so prominent in childhood that it is readily diagnosed by pediatricians. However, a mild form of the disease may only become apparent during adolescence or adulthood. We observed a brother and sister with subtle manifestations of the disease, which was discovered after the brother's son was diagnosed with typical GSD 1a. The adult siblings never suffered from hypoglycemia, had normal fasting blood glucose and liver transaminases at the time of diagnosis, and were taller than average for Chinese. Their only notable disease manifestations were recurrent gouty arthritis associated with hyperuricemia and hyperlipidemia during adolescence. When diagnosed, the brother had multiple benign and malignant hepatic tumors, and died of fulminant metastatic hepatocellular carcinoma 6months after liver transplantation. p.M121V/p.R83H and p.M121V/p.M121V genotypic constellations of the G6PC gene were identified in this family. Both siblings were homozygous for the newly identified p.M121V mutation. The infant had compound heterozygous mutations, p.R83H and p.M121V. We recommend that mild GSD should be considered in the adolescents with unexplained hyperuricemia and hyperlipidemia, despite the presence of normal blood glucose levels. This report also reminds us that hepatocellular carcinoma could develop even in very mild GSD 1a patients.     

Eight novel CARD15 variants detected by DNA sequence analysis of the CARD15 gene in 111 patients with inflammatory bowel disease

We performed a limited DNA sequence analysis of the CARD15 gene in 89 patients with Crohn’s disease (CD), 19 patients with ulcerative colitis (UC), and three patients with indeterminate colitis (IC), who were heterozygous carriers of one of the common CARD15 mutations [c.2104C>T (p.R702W), c.2722G>C (p.G908R), or c.3019_3020insC (p.Leu1007fsX1008)], the c.2462+10A>C variant, or of a new amino acid substitution in the 3′-end of exon 4. CARD15 exons 4, 5, 6, 8, and 11 were amplified by PCR and completely sequenced, thereby theoretically covering 73.9% of the described CARD15 variants and 96.6% of the mutated alleles. Using this approach, eight novel amino acid substitutions [c.1171C>T (p.R391C), c.1387C>G (p.P463A), c.2138G>A (p.R713H), c.2278C>T (p.R760C), c.2368C>T (p.R790W), c.2371C>T (p.R791W), c.2475C>G (p.N825K), and c.2546C>T (p.A849V)] were detected in six CD and two IC patients, and one UC patient. A severe disease phenotype was observed especially in patients who are compound-heterozygous for a common and a novel CARD15 mutation.Schnitzler and Brand contributed equally     

Analysis of the sphingomyelin phosphodiesterase 1 gene (SMPD1) in Turkish Niemann–Pick disease patients: Mutation profile and description of a novel mutation

Niemann–Pick disease (NPD) is a lysosomal storage disorder that results from the deficiency of a lysosomal enzyme, acid sphingomyelinase. Niemann–Pick disease type A and B is caused by mutations in the sphingomyelin phosphodiesterase gene (SMPD1) coding for ASM. The aim of this study was to evaluate the spectrum of SMPD1 gene mutations in Turkish NPD patients and to study genotype–phenotype associations. We present a molecular analysis of 10 Turkish NPD type A/B patients. Four of the patients had type A and six had type B NPD. All mutant SMPD1 alleles were identified, including 5 different mutations, 1 of which was novel. These mutations included three missense mutations: c.409T>C (p.L137P), c.1262 A>G (p.H421R) and c.1552T>C (p.L549P), a common frameshift mutation in codon 189, identified in three patients, is caused by the deletion of the 567T, introducing a stop codon 65 amino acids downstream (p.P189fsX65), and a novel frameshift mutation c.1755delC (p.P585PfsX24) which was not reported previously.     

Late-onset Krabbe disease is predominant in Japan and its mutant precursor protein undergoes more effective processing than the infantile-onset form

Krabbe disease is an autosomal recessive leukodystrophy caused by the deficiency of the galactocerebrosidase (GALC) enzyme. It is pathologically characterized by demyelination of the central and peripheral nervous systems by accumulation of galactosylsphingosine. To date, more than 120 mutations in the GALC gene have been reported worldwide and genotype–phenotype correlations have been reported in some types of mutations. In this study, we analyzed 22 unreported Japanese patients with Krabbe disease and summarized a total of 51 Japanese patients, including 29 previously reported patients. To elucidate how GALC mutations impair enzymatic activity, multiple disease-causing mutations including common mutations and polymorphisms were investigated for enzymatic activity and precursor processing ability with transient expression system. We also performed 3-D enzyme structure analysis to determine the effect of each new mutation. Five novel mutations were detected including one deletion c.1808delT [p.L603X], one nonsense mutation c.1023C>G [p.Y341X], and three missense mutations c.209T>C [p.L70P], c.1054G>A [p.G352R], and c.1937G>C [p.G646A]. For the total of 51 patients, 59% had late-onset forms of Krabbe disease. Seven common mutations accounted for 58% of mutant alleles of patients with Krabbe disease in Japan. Infantile-onset mutations had almost no enzyme activity, while late-onset mutations had 4%–20% of normal enzyme activity. The processing rate of precursor GALC protein to mature form was slower for infantile-onset mutations. Heat stability of the mutant proteins revealed that p.G270D was more stable compared to the other mutations. The constructed 3D-model showed that the residues for Krabbe mutations were less solvent-accessible and located in the core region of GALC protein. In conclusion, we have demonstrated that the most common phenotype in Japan is the late-onset type, that the enzyme activity for GALC mutants is correlated with mutational severity, and that the most pathogenic factor is due to the processing rate from the precursor to the mature protein.     

Three novel α-L-iduronidase mutations in 10 unrelated Chinese mucopolysaccharidosis type I families

Mucopolysaccharidosis type I (MPS I) arises from a deficiency in the α-L-iduronidase (IDUA) enzyme. Although the clinical spectrum in MPS I patients is continuous, it was possible to recognize 3 phenotypes reflecting the severity of symptoms, viz., the Hurler, Scheie and Hurler/Scheie syndromes. In this study, 10 unrelated Chinese MPS I families (nine Hurler and one Hurler/Scheie) were investigated, and 16 mutant alleles were identified. Three novel mutations in IDUA genes, one missense p.R363H (c.1088G > A) and two splice-site mutations (c.1190-1G > A and c.792+1G > T), were found. Notably, 45% (nine out of 20) and 30% (six out of 20) of the mutant alleles in the 10 families studied were c.1190-1G > A and c.792+1G > T, respectively. The novel missense mutation p.R363H was transiently expressed in CHO cells, and showed retention of 2.3% IDUA activity. Neither p.W402X nor p.Q70X associated with the Hurler phenotype, or even p.R89Q associated with the Scheie phenotype, was found in this group. Finally, it was noted that the Chinese MPS I patients proved to be characterized with a unique set of IDUA gene mutations, not only entirely different from those encountered among Europeans and Americans, but also apparently not even the same as those found in other Asian countries.     

Analysis of the CTNS gene in nephropathic cystinosis Mexican patients: report of four novel mutations and identification of a false positive 57-kb deletion genotype with LDM-2/exon 4 multiplex PCR assay

Objective: Identify CTNS gene mutations in nephropathic cystinosis Mexican patients. Subjects and Methods: Eleven patients were included, nine presenting infantile nephropathic cystinosis and two siblings with the juvenile phenotype. The common 57-kb deletion was detected by multiplex PCR using large deletion marker-2 (LDM-2)/exon 4 set primers. Those alleles negative for 57-kb deletion were screened by single strand confirmation polymorphism (SSCP) and subsequent direct sequencing. Results: In our sample, five mutations previously reported are identified: 57-kb deletion, EX4_EX5del, c.985_986insA, c.357_360delGACT, and c.537_557del. We detect a false assignation of 57-kb deletion homozygous genotype by using the LDM-2/exon 4 primers. In addition, four novel and severe mutations are identified: c.379delC, c.1090_1093delACCAinsCG, c.986C>G (p.T216R), and c.400+5G>A. Conclusions: Our sample of Mexican patients display allelic heterogeneity as compared to European or North American cystinosis cases. The identification of novel mutations might suggest the presence of exclusive American CTNS alleles in Mexican population. In order to prevent the false positive assignation of 57-kb deletion genotype, as caused by the presence of another type of intragenic CTNS gross deletion, we propose to analyze a different control CTNS exon to those originally reported in both LDM multiplex PCR assays, especially when parental DNA samples are not available.     

Genetic Basis of Glycogen Storage Disease Type 1a: Prevalent Mutations at the Glucose-6-Phosphatase Locus

Diagnosis of glycogen storage disease (GSD) type 1a currently is established by demonstrating the lack of glucose-6-phosphatase (G6Pase) activity in the patient's biopsied liver specimen. Recent cloning of the G6Pase gene and identification of mutations within the gene that causes GSD type 1a allow for the development of a DNA-based diagnostic method. Using SSCP analysis and DNA sequencing, we characterized the G6Pase gene of 70 unrelated patients with enzymatically confirmed diagnosis of GSD type 1a and detected mutations in all except 17 alleles (88%). Sixteen mutations were uncovered that were shown by expression to abolish or greatly reduce G6Pase activity and that therefore are responsible for the GSD type 1a disorder. R83C and Q347X are the most prevalent mutations found in Caucasians, 130X and R83C are most prevalent in Hispanics, and R83H is most prevalent in Chinese. The Q347X mutation has thus far been identified only in Caucasian patients, and the 130X mutation has been identified only in Hispanic patients. Our results demonstrate that the DNA-based analysis can accurately, rapidly, and noninvasively detect the majority of mutations in GSD type 1a. This DNA-based diagnosis now permits prenatal diagnosis among at-risk patients and serves as a database in screening and counseling patients clinically suspected of having this disease.     

Detection of the frequencies of GBA gene major mutations in patients with Gaucher disease in Ukraine

The molecular diagnostics of 27 from 26 Ukrainian families has been performed. The common mutations in GBA gene (N370S, L444P and 84GG) accounted for up to 58% of all cases: mutation N370S was detected in 42.3% alleles, mutation L444P was observed in 15.4% alleles and mutation 84GG was not found at all. The other mutations were: P178S, W184R and Rec Nci I (in compounds with N370S) in the patients with nonneuronopathic form of Gaucher disease, and the genotypes G377S/c 999G --> A and D409H/R120W/G202R were detected in patients with chronic neuronopathic form of Gaucher disease. The data analysis of the genotype and disease progression in the patients allows confirming the known genotype-phenotype correlation.     

An association among iron,copper, zinc,and selenium,and antioxidative status in dyslipidemic pediatric patients with glycogen storage disease types IA and III

Dyslipidemia in patients with glycogen storage disease types Ia (GSD Ia) and III (GSD III) does not lead to premature atherosclerosis. The aim of this study was to investigate the association among serum copper (Cu), zinc (Zn), iron (Fe), and selenium (Se) concentrations, and their carrier proteins: ceruloplasmin, albumin, and related antioxidant enzyme activities [superoxide dismutase (SOD), catalase (CAT), glutathione peroxidase (GPx), paraoxonase (PON), and arylesterase (ARYL)] in 20 GSD Ia and 14 III patients compared to age and sex matched 20 healthy subjects. Erythrocyte oxidative stress was measured by erythrocyte thiobarbituric acid reactive substances (eTBARSs). Hypertriglyceridemia [333 (36–890) mg/dL] in GSD Ia and hypercholesterolemia with elevated LDL-cholesterol [188 (91–313) mg/dL] and decreased HDL-cholesterol [32(23–58) mg/dL] levels in GSD III were found. Serum Cu, Fe, and Zn showed no significant differences between groups. However, Se 60 (54–94), 81 (57–127) μg/L, ceruloplasmin 21 (10–90), 27 (23–65) μg/L, and albumin 2.4 (1.7–5.1), 2.8 (1.8–4.06) g/dL levels were decreased in GSD Ia and III groups, respectively, in comparison with the controls [Se 110 (60–136) μg/L, ceruloplasmin 72 (32–94) μg/L, and albumin 4.4 (4–4.8) g/dL)]. In spite of high oxidative stress in erythrocyte detected by elevated eTBARS/Hb levels in GSD group [674.8 (454.6–948.2) for GSD Ia, 636.3 (460.9–842.1) for GSD III, and 525.6 (449.2–612.6)], the activities of CAT, SOD, ARYL, and PON in GSD patients were not different from the controls. GPx activity was decreased in GSD Ia [3.7 (1.8–7.1) U/mL] and GSD III [4.2 (2.2–8.6) U/mL] compared with healthy controls [7.1 (2.9–16.2) U/mL].In conclusion, this study supplied the data for trace elements, their carrier, and antioxidative enzymes in the patients with GSD Ia and III. The trace elements and anti-oxidative enzyme levels in GSD patients failed to explain the atherosclerotic escape phenomenon reported in these patients.     

CFTR haplotypes in northern Iranian population

Background

Cystic fibrosis (CF) is a multiorganic autosomal recessive disorder, caused by mutation in cystic fibrosis transmembrane conductance regulator (CFTR). CF is highly heterogeneous in Iranian population and molecular diagnosis based on direct identification of mutations is not completely efficient. The use of polymorphic intragenic markers not only can facilitate phenotype prediction in prenatal diagnosis by gene tracking, but also can lead to the demonstration of possible associations between haplotypes and specific mutations.

Methods

60 CF patients and 53 fertile normal subjects originating from North of Iran were analyzed for F508del mutation and c.1210-12T(5_9), c.1408A>G and c.744-33GATT(6_8) polymorphisms.

Results

c.1210-12T[7] is the most prevalent allele in normal individuals and CF non-F508del patients with 87.7%and 86.7% frequencies respectively. c.1408A>G survey showed that frequency of allele G and A is nearly equal in both non-F508del CF patients and normal individuals. c.744-33GATT(6_8) study showed that 7 repeat is the most prevalent allele in normal individuals and non-F508del CF patients with 80.2% and 82.1% frequencies respectively. The [c.1408A; c.1210-12T[9]; c.744-33GATT[6]] haplotype was only associated with mutant alleles including F508del.

Conclusions

The allelic distribution and heterozygosity results suggest that c.1408A>G, c.1210-12T(5_9) and c.744-33GATT(6_8) can contribute to carrier detection and prenatal diagnosis of CF in Iranian families with previous history of the disease.     

Characterization of seven novel mutations on the HEXB gene in French Sandhoff patients

Sandhoff disease (SD) is an autosomal recessive lysosomal storage disease caused by mutations in the HEXB gene encoding the beta subunit of hexosaminidases A and B, two enzymes involved in GM2 ganglioside degradation. Eleven French Sandhoff patients with infantile or juvenile forms of the disease were completely characterized using sequencing of the HEXB gene. A specific procedure was developed to facilitate the detection of the common 5′-end 16 kb deletion which was frequent (36% of the alleles) in our study. Eleven other disease-causing mutations were found, among which four have previously been reported (c.850C>T, c.793T>G, c.115del and c.800_817del). Seven mutations were completely novel and were analyzed using molecular modelling. Two deletions (c.176del and c.1058_1060del), a duplication (c.1485_1487dup) and a nonsense mutation (c.552T>G) were predicted to strongly alter the enzyme spatial organization. The splice mutation c.558+5G>A affecting the intron 4 consensus splice site led to a skipping of exon 4 and to a truncated protein (p.191X). Two missense mutations were found among the patients studied. The c.448A>C mutation was probably a severe mutation as it was present in association with the known c.793T>G in an infantile form of Sandhoff disease and as it significantly modified the N-terminal domain structure of the protein. The c.171G>C mutation resulting in a p.W57C amino acid substitution in the N-terminal region is probably less drastic than the other abnormalities as it was present in a juvenile patient in association with the c.176del. Finally, this study reports a rapid detection of the Sandhoff disease-causing alleles facilitating genetic counselling and prenatal diagnosis in at-risk families.     

Identifying a novel mutation of CYP17A1 gene from five Chinese 17α-hydroxylase/17, 20-lyase deficiency patients

Mutations of CYP17A1 gene could cause complete or partial, combined or isolated 17α-hydroxylase/17,20-lyase enzyme deficiencies (17OHD). We intended to investigate the CYP17A1 mutation in five unrelated patients and analyze its possible influence on phenotype of an atypical 17OHD patient presented with micropenis, hypertension and intermittent hypokalemia. Steroid hormones were assayed in these patients. A novel missense mutation (c.1169C>G, p. Thr390Arg) located in exon 7 was detected in one of the patients. Homozygous c. 985_987delinsAA, p. Tyr329fs mutation was found in two patients, while compound heterozygous mutations (c. 985_987delinsAA, p. Tyr329fs/c. 932–939 del, p. Val311fs and c. 287G>A, p. Arg96Gln/c. 985_987delinsAA, p. Tyr329fs) were found in two other patients, respectively. Then, steric model analysis of CYP17A1 showed that the novel mutation T390R changed the local structure as well as the electrostatic potential of the nearby beta sheet. Finally, site-directed mutagenesis and in vitro expression were used to analyze the activity of novel mutant CYP17A1. It indicated the T390R mutant retained part of enzyme activity, which was consistent to the clinical features. In conclusion, we identified a novel missense mutation of CYP17A1 gene from a patient with micropenis, hypertension and intermittent hypokalemia, which varied from other four patients. It also expanded our understanding of genotype–phenotype correlation of the disease.     

Mutations in the glucose-6-phosphate transporter (G6PT) gene in patients with glycogen storage diseases type 1b and 1c.

Glycogen storage diseases type 1 (GSD 1) are a group of autosomal recessive disorders characterized by impairment of terminal steps of glycogenolysis and gluconeogenesis. Mutations of the glucose-6-phosphatase gene are responsible for the most frequent form of GSD 1, the subtype 1a, while mutations of the glucose-6-phosphate transporter gene (G6PT) have recently been shown to cause the non 1a forms of GSD, namely the 1b and 1c subtypes. Here, we report on the analysis by single-stranded conformation polymorphism (SSCP) and/or DNA sequencing of the exons of the G6PT in 14 patients diagnosed either as affected by the GSD 1b or 1c subtypes. Mutations in the G6PT gene were found in all patients. Four of the detected mutations were novel mutations, while the others were previously described. Our results confirm that the GSD 1b and 1c forms are due to mutations in the same gene, i.e. the G6PT gene. We also show that the same kind of mutation can be associated or not with evident clinical complications such as neutrophil impairment. Since no correlation between the type and position of the mutation and the severity of the disease was found, other unknown factors may cause the expression of symptoms, such as neutropenia, which dramatically influence the severity of the disease.