A novel frameshift PHKA2 mutation in a family with glycogen storage disease type IXa: A first report in Vietnam and review of literature.

BACKGROUND: Glycogen storage diseases (GSDs) are clinically and genetically heterogeneous disorders. Overlapping features between liver GSDs are a major challenge in the clinical diagnosis of them. Genetic testing can provide an early and accurate diagnosis of patients suspected with GSDs. CASE PRESENTATION: In this study, we report two siblings born to healthy, non-consanguineous Vietnamese parents with hepatomegaly. The proband presented with hepatomegaly, normal spleen, elevated transaminases, without hypoglycemia, normal lactate dehydrogenase and creatine kinase. Liver biopsy revealed degeneration and swollen hepatocytes, suggesting a diagnosis with GSDs. METHODS: Whole exome sequencing was applied to identify genetic variants in the proband. Variant validation and familial co-segregation analysis were examined using Sanger sequencing. RESULTS: A novel frameshift duplication mutation c.3308_3312dupATGTC (p.L1105Mfs*11) of the PHKA2 gene was identified in the proband and his elder brother at the hemizygous state. This mutation was inherited from their mother. Their father and younger brother were normal genotype. CONCLUSIONS: The two siblings were accurately diagnosed with GSD type XIa. This is the first case report of GSD type IXa in Vietnamese patients with a mutation in the PHKA2 gene. This finding may support for genetics diagnosis of unknown cause of hepatomegaly.

Autosomal recessive Noonan syndrome associated with biallelic LZTR1 variants.

PURPOSE: To characterize the molecular genetics of autosomal recessive Noonan syndrome. METHODS: Families underwent phenotyping for features of Noonan syndrome in children and their parents. Two multiplex families underwent linkage analysis. Exome, genome, or multigene panel sequencing was used to identify variants. The molecular consequences of observed splice variants were evaluated by reverse-transcription polymerase chain reaction. RESULTS: Twelve families with a total of 23 affected children with features of Noonan syndrome were evaluated. The phenotypic range included mildly affected patients, but it was lethal in some, with cardiac disease and leukemia. All of the parents were unaffected. Linkage analysis using a recessive model supported a candidate region in chromosome 22q11, which includes LZTR1, previously shown to harbor mutations in patients with Noonan syndrome inherited in a dominant pattern. Sequencing analyses of 21 live-born patients and a stillbirth identified biallelic pathogenic variants in LZTR1, including putative loss-of-function, missense, and canonical and noncanonical splicing variants in the affected children, with heterozygous, clinically unaffected parents and heterozygous or normal genotypes in unaffected siblings. CONCLUSION: These clinical and genetic data confirm the existence of a form of Noonan syndrome that is inherited in an autosomal recessive pattern and identify biallelic mutations in LZTR1.

An ABCC8 Nonsense Mutation Causing Neonatal Diabetes Through Altered Transcript Expression.

The pancreatic ATP-sensitive K+ (K-ATP) channel is a key regulator of insulin secretion. Gain-of-function mutations in the genes encoding the Kir6.2 (KCNJ11) and SUR1 (ABCC8) subunits of the channel cause neonatal diabetes, whilst loss-of-function mutations in these genes result in congenital hyperinsulinism. We report two patients with neonatal diabetes in whom we unexpectedly identified recessively inherited loss-of-function mutations. The aim of this study was to investigate how a homozygous nonsense mutation in ABCC8 could result in neonatal diabetes. The ABCC8 p.Glu747* was identified in two unrelated Vietnamese patients. This mutation is located within the in-frame exon 17 and RNA studies confirmed (a) the absence of full length SUR1 mRNA and (b) the presence of the alternatively spliced transcript lacking exon 17. Successful transfer of both patients to sulphonylurea treatment suggests that the altered transcript expression enhances the sensitivity of the K-ATP channel to Mg-ADP/ATP. This is the first report of an ABCC8 nonsense mutation causing a gain-of-channel function and these findings extend the spectrum of K-ATP channel mutations observed in patients with neonatal diabetes.

Hematopoietic Stem Cell Transplantation for Patients with Mucopolysaccharidosis II.

There is limited information regarding the long-term outcomes of hematopoietic stem cell transplantation (HSCT) for mucopolysaccharidosis II (MPS II). In this study, clinical, biochemical, and radiologic findings were assessed in patients who underwent HSCT and/or enzyme replacement therapy (ERT). Demographic data for 146 HSCT patients were collected from 27 new cases and 119 published cases and were compared with 51 ERT and 15 untreated cases. Glycosaminoglycan (GAG) levels were analyzed by liquid chromatography tandem mass spectrometry in blood samples from HSCT, ERT, and untreated patients as well as age-matched controls. Long-term magnetic resonance imaging (MRI) findings were investigated in 13 treated patients (6 ERT and 7 HSCT). Mean age at HSCT was 5.5 years (range, 2 to 21.4 years) in new patients and 5.5 years (range, 10 months to 19.8 years) in published cases. None of the 27 new patients died as a direct result of the HSCT procedure. Graft-versus-host disease occurred in 8 (9%) out of 85 published cases, and 9 (8%) patients died from transplantation-associated complications. Most HSCT patients showed greater improvement in somatic features, joint movements, and activity of daily living than the ERT patients. GAG levels in blood were significantly reduced by ERT and levels were even lower after HSCT. HSCT patients showed either improvement or no progression of abnormal findings in brain MRI while abnormal findings became more extensive after ERT. HSCT seems to be more effective than ERT for MPS II in a wide range of disease manifestations and could be considered as a treatment option for this condition.

Glycosaminoglycan levels in dried blood spots of patients with mucopolysaccharidoses and mucolipidoses.

Mucopolysaccharidoses (MPSs) and mucolipidoses (ML) are groups of lysosomal storage disorders in which lysosomal hydrolases are deficient leading to accumulation of undegraded glycosaminoglycans (GAGs), throughout the body, subsequently resulting in progressive damage to multiple tissues and organs. Assays using tandem mass spectrometry (MS/MS) have been established to measure GAGs in serum or plasma from MPS and ML patients, but few studies were performed to determine whether these assays are sufficiently robust to measure GAG levels in dried blood spots (DBS) of patients with MPS and ML. MATERIAL AND METHODS: In this study, we evaluated GAG levels in DBS samples from 124 MPS and ML patients (MPS I=16; MPS II=21; MPS III=40; MPS IV=32; MPS VI=10; MPS VII=1; ML=4), and compared them with 115 age-matched controls. Disaccharides were produced from polymer GAGs by digestion with chondroitinase B, heparitinase, and keratanase II. Subsequently, dermatan sulfate (DS), heparan sulfate (HS-0S, HS-NS), and keratan sulfate (mono-sulfated KS, di-sulfated KS, and ratio of di-sulfated KS in total KS) were measured by MS/MS. RESULTS: Untreated patients with MPS I, II, VI, and ML had higher levels of DS compared to control samples. Untreated patients with MPS I, II, III, VI, and ML had higher levels of HS-0S; and untreated patients with MPS II, III and VI and ML had higher levels of HS-NS. Levels of KS were age dependent, so although levels of both mono-sulfated KS and di-sulfated KS were generally higher in patients, particularly for MPS II and MPS IV, age group numbers were not sufficient to determine significance of such changes. However, the ratio of di-sulfated KS in total KS was significantly higher in all MPS patients younger than 5years old, compared to age-matched controls. MPS I and VI patients treated with HSCT had normal levels of DS, and MPS I, VI, and VII treated with ERT or HSCT had normal levels of HS-0S and HS-NS, indicating that both treatments are effective in decreasing blood GAG levels. CONCLUSION: Measurement of GAG levels in DBS is useful for diagnosis and potentially for monitoring the therapeutic efficacy in MPS.

The clinical features of osteogenesis imperfecta in Vietnam.

PURPOSE: Osteogenesis imperfecta (OI) has not been studied in a Vietnamese population before. The aim of this study was to systematically collect epidemiological information, investigate clinical features and create a clinical database of OI patients in Vietnam for future research and treatment strategy development. METHOD: Participants underwent clinical and physical examinations; also medical records were reviewed. Genealogical information was collected and family members' phenotypical manifestations recorded. Cases were classified according to the Sillence classification. RESULTS: In total, 146 OI patients from 120 families were studied: 46 with OI Type I, 46 with Type III and 54 with Type IV. Almost patients had skeletal deformations. One hundred and forty-two had a history of fractures, 117 blue sclera, 89 dentinogenesis imperfecta and 26 hearing loss. The total number of fractures was 1,932. Thirty-four patients had intra-uterine fractures and nine had perinatal fractures. Surgery was performed 163 times in 58 patients; 100 osteosyntheses and 63 osteotomies. Bisphosphonate treatment was used in 37 patients. The number of affected individuals and predominance of severe forms of OI indicate that the disease is under diagnosed in Vietnam, especially in cases without a family history or with mild form of OI. Deformities appeared in all patients with different severity and localisation, affecting mostly the lower limbs. OI medical and surgical treatment rates are low and in most cases surgery was performed due to fractures. CONCLUSIONS: Compared to previous studies, our results indicate a lower OI prevalence and greater severity of symptoms in the Vietnamese population when compared with other areas. Further investigation, improved diagnosis and treatment are needed to increase the patients' quality of life.

Therapies for the bone in mucopolysaccharidoses.

Patients with mucopolysaccharidoses (MPS) have accumulation of glycosaminoglycans in multiple tissues which may cause coarse facial features, mental retardation, recurrent ear and nose infections, inguinal and umbilical hernias, hepatosplenomegaly, and skeletal deformities. Clinical features related to bone lesions may include marked short stature, cervical stenosis, pectus carinatum, small lungs, joint rigidity (but laxity for MPS IV), kyphoscoliosis, lumbar gibbus, and genu valgum. Patients with MPS are often wheelchair-bound and physical handicaps increase with age as a result of progressive skeletal dysplasia, abnormal joint mobility, and osteoarthritis, leading to 1) stenosis of the upper cervical region, 2) restrictive small lung, 3) hip dysplasia, 4) restriction of joint movement, and 5) surgical complications. Patients often need multiple orthopedic procedures including cervical decompression and fusion, carpal tunnel release, hip reconstruction and replacement, and femoral or tibial osteotomy through their lifetime. Current measures to intervene in bone disease progression are not perfect and palliative, and improved therapies are urgently required. Enzyme replacement therapy (ERT), hematopoietic stem cell transplantation (HSCT), and gene therapy are available or in development for some types of MPS. Delivery of sufficient enzyme to bone, especially avascular cartilage, to prevent or ameliorate the devastating skeletal dysplasias remains an unmet challenge. The use of an anti-inflammatory drug is also under clinical study. Therapies should start at a very early stage prior to irreversible bone lesion, and damage since the severity of skeletal dysplasia is associated with level of activity during daily life. This review illustrates a current overview of therapies and their impact for bone lesions in MPS including ERT, HSCT, gene therapy, and anti-inflammatory drugs.

Mucopolysaccharidosis IVA: correlation between genotype, phenotype and keratan sulfate levels.

Mucopolysaccharidosis IVA (MPS IVA) is caused by deficiency of N-acetylgalactosamine-6-sulfate sulfatase (GALNS), leading to systemic skeletal dysplasia because of excessive storage of keratan sulfate (KS) in chondrocytes. In an effort to determine a precise prognosis and personalized treatment, we aim to characterize clinical, biochemical, and molecular findings in MPS IVA patients, and to seek correlations between genotype, phenotype, and blood and urine KS levels. Mutation screening of GALNS gene was performed in 55 MPS IVA patients (severe: 36, attenuated: 13, undefined: 6) by genomic PCR followed by direct sequence analysis. Plasma and urine KS levels were measured by ELISA method. Genotype/phenotype/KS correlations were assessed when data were available. Fifty-three different mutations including 19 novel ones (41 missense, 2 nonsense, 4 small deletions, 1 insertion, and 5 splice-site) were identified in 55 patients and accounted for 93.6% of the analyzed mutant alleles. Thirty-nine mutations were associated with a severe phenotype and ten mutations with an attenuated one. Blood and urine KS concentrations in MPS IVA patients were age-dependent and markedly higher than those in age-matched normal controls. Plasma and urine KS levels in MPS IVA patients with the severe phenotype were higher than in those with an attenuated form. This study provides evidence for extensive allelic heterogeneity of MPS IVA. Accumulation of mutations as well as clinical descriptions and KS levels allows us to predict clinical severity more precisely and should be used for evaluation of responses to potential treatment options.

Dermatan sulfate and heparan sulfate as a biomarker for mucopolysaccharidosis I.

Mucopolysaccharidosis I (MPS I) is an autosomal recessive disorder caused by deficiency of alpha-L-iduronidase leading to accumulation of its catabolic substrates, dermatan sulfate (DS) and heparan sulfate (HS), in lysosomes. This results in progressive multiorgan dysfunction and death in early childhood. The recent success of enzyme replacement therapy (ERT) for MPS I highlights the need for biomarkers that reflect response to such therapy. To determine which biochemical markers are better, we determined serum and urine DS and HS levels by liquid chromatography tandem mass spectrometry in ERT-treated MPS I patients. The group included one Hurler, 11 Hurler/Scheie, and two Scheie patients. Seven patients were treated from week 1, whereas the other seven were treated from week 26. Serum and urine DS (DeltaDi-4S/6S) and HS (DeltaDiHS-0S, DeltaDiHS-NS) were measured at baseline, week 26, and week 72. Serum DeltaDi-4S/6S, DeltaDiHS-0S, and DeltaDiHS-NS levels decreased by 72%, 56%, and 56%, respectively, from baseline at week 72. Urinary glycosaminoglycan level decreased by 61.2%, whereas urine DeltaDi-4S/6S, DeltaDiHS-0S, and DeltaDiHS-NS decreased by 66.8%, 71.8%, and 71%, respectively. Regardless of age and clinical severity, all patients showed marked decrease of DS and HS in blood and urine samples. We also evaluated serum DS and HS from dried blood-spot samples of three MPS I newborn patients, showing marked elevation of DS and HS levels compared with those in control newborns. In conclusion, blood and urine levels of DS and HS provide an intrinsic monitoring and screening tool for MPS I patients.

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.

Acidic amino acid tag enhances response to enzyme replacement in mucopolysaccharidosis type VII mice.

We have tested an acidic oligopeptide-based targeting system for delivery of enzymes to tissues, especially bone and brain, in a murine mucopolysaccharidosis type VII (MPS VII) model. This strategy is based upon tagging a short peptide consisting of acidic amino acids (AAA) to N terminus of human beta-glucuronidase (GUS). The pharmacokinetics, biodistribution, and the pathological effect on MPS VII mouse after 12 weekly infusions were determined for recombinant human untagged and tagged GUS. The tagged GUS was taken up by MPS VII fibroblasts in a mannose 6-phosphate receptor-dependent manner. Intravenously injected AAA-tagged enzyme had five times more prolonged blood clearance compared with the untagged enzyme. The tagged enzyme was delivered effectively to bone, bone marrow, and brain in MPS VII mice and was effective in reversing the storage pathology. The storage in osteoblasts was cleared similarly with both enzyme types. However, cartilage showed a little response to any of the enzymes. The tagged enzyme reduced storage in cortical neurons, hippocampus, and glia cells. A highly sensitive method of tandem mass spectrometry on serum indicated that the concentration of serum dermatan sulfate and heparan sulfate in mice treated with the tagged enzyme decreased more than the untagged enzyme. These preclinical studies suggest that this AAA-based targeting system may enhance enzyme-replacement therapy.

Murine model (Galns(tm(C76S)slu)) of MPS IVA with missense mutation at the active site cysteine conserved among sulfatase proteins.

Mucopolysaccharidosis IVA (MPS IVA) is an autosomal recessive disorder caused by deficiency of N-acetylgalactosamine-6-sulfate sulfatase (GALNS), required for degradation of keratan sulfate and chondroitin-6-sulfate. In order to study the effects of a missense mutation in the active site cysteine in the GALNS gene that is conserved in all mammalian sulfatases, we produced a p.C76S (an active site replacement) knock-in mouse by replacing the Cys76 with Ser in the endogenous murine Galns by targeted mutagenesis. Homozygous Galns(tm(C76S)slu) mice had no detectable GALNS enzyme activity. At age of 2-4 months, lysosomal storage was present primarily within reticuloendothelial cells such as Kupffer cells and spleen sinusoidal lining cells. Vacuolar change was present in glomerular visceral epithelial cells and was not present in hepatocytes or renal tubular cells. In the brain, hippocampal and neocortical neurons and meningeal cells showed lysosomal storage. Radiographs revealed no change in the skeletal bones of mice up to 12 months old. Thus, the Galns(tm(C76S)slu) mice had visceral storage of GAGs in organs but lacked the skeletal features of human MPS IVA. In contrast to a previously reported transgenic model (Galns(tm(hC79S.mC76S)slu)), in which the inactive human GALNS transgene was overexpressed, no reduction in other sulfatases was observed. In addition, the Galns(tm(C76S)slu) mice displayed milder storage. We conclude that the milder phenotype is characteristic of isolated GALNS deficiency while the more severe phenotype reflected in the Galns(tm(hC79S.mC76S)slu) mice was due to deficiency of other sulfatases caused by oversaturation of the sulfate modifying enzyme by the inactive human gene product.