Analysis of gene mutations in Chinese patients with maple syrup urine disease

Identification of gene mutations in six Chinese patients with maple syrup urine disease

Background: Maple syrup urine disease (MSUD) is a rare autosomal recessive amino acid metabolic disease. This study is to identify the pathogenic genetic factors of six cases of MUSD and evaluates the application value of high-throughput sequencing technology in the early diagnosis of MUSD. Methods: Clinical examination was carried out for patients and used blood tandem mass spectrometry (MS/MS), urine gas chromatography-mass spectrometry (GC/MS), and the application of high-throughput sequencing technology for detection. Validate candidate mutations by polymerase chain reaction (PCR)-Sanger sequencing technology. Bioinformatics software analyzed the variants' pathogenicity. Using Swiss PDB Viewer software to predict the effect of mutation on the structure of BCKDHA and BCKDHB proteins. Result: A total of six MSUD patients were diagnosed, including four males and two females. Nine variants were found in three genes of six MSUD families by high-throughput sequencing, including four missense mutations: c.659C>T(p.A220V), c.818C>T(p.T273I), c.1134C>G(p.D378E), and c.1006G>A(p.G336S); two non-sense mutations: c.1291C>T(p.R431*) and c.331C>T(p.R111*); three deletion mutations: c.550delT (p.S184Pfs*46), c.718delC (p.P240Lfs*14), and c.795delG (p.N266Tfs*64). Sanger sequencing's results were consistent with the high-throughput sequencing. The bioinformatics software revealed that the mutations were harmful, and the prediction results of Swiss PDB Viewer suggest that variation affects protein conformation. Conclusion: This study identified nine pathogenic variants in the BCKDHA, BCKDHB, and DBT genes in six MSUD families, including two novel pathogenic variants in the BCKDHB gene, which enriched the genetic mutational spectrum of the disease. High-throughput sequencing is essential for the MSUD's differential diagnosis, early treatment, and prenatal diagnosis.

Three novel mutations of the BCKDHA, BCKDHB and DBT genes in Chinese children with maple syrup urine disease

BACKGROUND

Maple syrup urine disease (MSUD) is a rare metabolic autosomal recessive disorder caused by deficiency of the branched-chain α-ketoacid dehydrogenase complex. Mutations in the BCKDHA, BCKDHB and DBT genes are responsible for MSUD. This study presents the clinical and molecular characterizations of four MSUD patients.

METHODS

Clinical data of patients were retrospectively analyzed, and genetic mutations were identified by whole-exome sequencing. CLUSTALX was employed to analyzed cross-species conservation of the mutant amino acid. The impact of the mutations was analyzed with PolyPhen-2 software. The I-TASSER website and PyMOL software were used to predict the protein three-position structure of the novel mutations carried by the patients.

RESULTS

Vomiting, irritability, feeding difficulties, seizures, dyspnoea, lethargy and coma were the main clinical presentations of MSUD. Cranial MRI showed abnormal symmetrical signals in accordance with the presentation of inherited metabolic encephalopathy. Seven mutations were detected in four patients, including three novel pathogenic mutations in the BCKDHA (c.656C>A), BCKDHB (deletion of a single-copy of BCKDHB) and DBT (c.1219dup) genes. Structural changes were compatible with the observed phenotypes.

CONCLUSIONS

Different types of MSUD can display heterogeneous clinical manifestations. Exhaustive molecular studies are necessary for a proper differential diagnosis. The newly identified mutation will play a key role in the prenatal diagnosis of MSUD in the future.

Genetic analysis by targeted next-generation sequencing and novel variation identification of maple syrup urine disease in Chinese Han population

Maple syrup urine disease (MSUD) is a rare autosomal recessive disorder that affects the degradation of branched chain amino acids (BCAAs). Only a few cases of MSUD have been documented in Mainland China. In this report, 8 patients (4 females and 4 males) with MSUD from 8 unrelated Chinese Han families were diagnosed at the age of 6 days to 4 months. All the coding regions and exon/intron boundaries of BCKDHA, BCDKHB, DBT and DLD genes were analyzed by targeted NGS in the 8 MSUD pedigrees. Targeted NGS revealed 2 pedigrees with MSUD Ia, 5 pedigrees with Ib, 1 pedigree with MSUD II. Totally, 13 variants were detected, including 2 variants (p.Ala216Val and p.Gly281Arg) in BCKDHA gene, 10 variants (p.Gly95Ala, p.Ser171Pro, p.Phe175Leu, p.Arg183Trp, p.Lys222Thr, p.Arg285Ter, p.Arg111Ter, p.S184Pfs*46, p.Arg170Cys, p.I160Ffs*25) in BCKDHB gene, 1 variant (p.Arg431Ter) in DBT gene. In addition, 4 previously unidentified variants (p.Gly281Arg in BCKDHA gene, p.Ser171Pro, p.Gly95Ala and p.Lys222Thr in BCKDHB gene) were identified. NGS plus Sanger sequencing detection is effective and accurate for gene diagnosis. Computational structural modeling indicated that these novel variations probably affect structural stability and considered as likely pathogenic variants.

Maple syrup urine disease in Brazilian patients: variants and clinical phenotype heterogeneity

Background

Maple syrup urine disease (MSUD) is an autosomal recessive inherited metabolic disease caused by deficient activity of the branched-chain α-keto acid dehydrogenase (BCKD) enzymatic complex. BCKD is a mitochondrial complex encoded by BCKDHA, BCKDHB, DBT, and DLD genes. MSUD is predominantly caused by Variants in BCKDHA, BCKDHB, and DBT genes encoding the E1α, E1β, and E2 subunits of BCKD complex, respectively. The aim of this study was to characterize the genetic basis of MSUD by identifying the point variants in BCKDHA, BCKDHB, and DBT genes in a cohort of Brazilian MSUD patients and to describe their phenotypic heterogeneity. It is a descriptive cross-sectional study with 21 MSUD patients involving molecular genotyping by Sanger sequencing.

Results

Eight new variants predicted as pathogenic were found between 30 variants (damaging and non-damaging) identified in the 21 patients analyzed: one in the BCKDHA gene (p.Tyr120Ter); five in the BCKDHB gene (p.Gly131Val, p.Glu146Glnfs * 13, p.Phe149Cysfs * 9, p.Cys207Phe, and p.Lys211Asn); and two in the DBT gene (p.Glu148Ter and p.Glu417Val). Seventeen pathogenic variants were previously described and five variants showed no pathogenicity according to in silico analysis.

Conclusion

Given that most of the patients received late diagnoses, the study results do not allow us to state that the molecular features of MSUD variant phenotypes are predictive of clinical severity.

Identification of eight novel mutations in 11 Chinese patients with maple syrup urine disease

BACKGROUND

Maple syrup urine disease (MSUD) is an autosomal recessive inherited disorder that affects the degradation of branched-chain amino acids and is associated with acute and chronic brain dysfunction. This study presents 11 new patients with MSUD and describes the clinical characteristics and gene mutations reported in Chinese individuals.

METHODS

During 2011-2018, 11 pedaitric patients with MSUD from 11 Chinese families were analyzed based on clinical characteristics and mass spectrometry, with confirmation via gene sequencing. Novel mutations affecting protein function were predicted with Mutation-Taster, PolyPhen-2, CADD and SIFT software. 3D models of the mutated proteins were generated by using the SWISS-MODEL online server, and the models were visualized in PyMOL. The characteristics and gene mutations in patients with MSUD were analyzed retrospectively.

RESULTS

Seventeen mutations in the BCKDHA, BCKDHB and DBT genes were found, 8 of which are novel: c.55C>/T, c.349C>T, c.565C>T, c.808G>A, c.859C>G, and c.1270dupC in BCKDHA; c.275-2A>G in BCKDHB; and c.1291C>T in DBT. Eight patients died. Two patients had severe mental retardation and were physically handicapped. One patient with the intermediate type had relatively good prognosis, with mild psychomotor retardation and adiposity. Four mothers underwent amniocentesis for prenatal diagnosis during their second pregnancy; two fetuses were wild type, and two were carriers of one heterozygous mutation.

CONCLUSIONS

Eight novel mutations were associated with MSUD in Chinese patients. Prenatal diagnosis was successfully performed by genetic analysis. Mutations in the BCKDHB gene were found in the majority of Chinese patients with MSUD.

Identification of six novel mutations in five infants with suspected maple syrup urine disease based on blood and urine metabolism screening

Maple syrup urine disease (MSUD) is a rare autosomal recessive genetic metabolic disease, with a high incidence rate in infants. We analyzed the data of molecular genetic analysis of five infants whose metabolism screening suspected MSUD and described their clinical symptoms. Further, we performed next-generation sequencing and Sanger sequencing to determine the genetic causes of the disease. Bioinformatics tools were used to predict the pathogenicity of novel mutations by performing structural modeling. All the five infants showed symptoms before one year of age and had elevated plasma leucine and valine levels. Among them, four infants presented an obvious increase in the urine lactic acid level. We identified the genetic cause of the disease in four infants and analyzed the pathogenicity of six novel mutations, viz., two mutations in BCKDHA (p.Gly180Asp and p.Arg265Gln), three in BCKDHB (p.Tyr169Cys, p.Ala331Thr, and p.Gly336Ser), and one in DBT (p.Leu69Arg), using in silico analysis. We also reviewed previously reported mutations in Chinese patients and summarized their genotypic and phenotypic characteristics. Our study has confirmed or corrected the clinical diagnosis and enriched the mutation spectrum of BCKDHA, BCKDHB, and DBT. We suggest blood and urine metabolism screening combined with next generation sequencing to diagnose MSUD, especially in infants, to achieve early diagnosis and early treatment.

Maple syrup urine disease mutation spectrum in a cohort of 40 consanguineous patients and insilico analysis of novel mutations

Maple syrup urine disease is the primary aminoacidopathy affecting branched-chain amino acid (BCAA) metabolism. The disease is mainly caused by the deficiency of an enzyme named branched-chained α-keto acid dehydrogenase (BCKD), which consist of four subunits (E1α, E1β, E2, and E3), and encoded by BCKDHA, BCKDHB, DBT, and DLD gene respectively. BCKD is the main enzyme in the catabolism pathway of BCAAs. Hight rate of autosomal recessive disorders is expected from consanguineous populations like Iran. In this study, we selected two sets of STR markers linked to the four genes, that mutation in which can result in MSUD disease. The patients who had a homozygous haplotype for selected markers of the genes were sequenced. In current survey, we summarized our recent molecular genetic findings to illustrate the mutation spectrum of MSUD in our country. Ten novel mutations including c.484 A > G, c.834_836dup CAC, c.357del T, and c. (343 + 1_344-1) _ (742 + 1_743-1)del in BCKDHB, c.355-356 ins 7 nt ACAAGGA, and c.703del T in BCKDHA, and c.363delCT/c.1238 T > C, c. (433 + 1_434-1) _ (939 + 1_940-1)del, c.1174 A > C, and c.85_86ins AACG have been found in DBT gene. Additionally, structural models of MSUD mutations have been performed to predict the pathogenicity of the newly identified variants.

Fourteen new mutations of BCKDHA, BCKDHB and DBT genes associated with maple syrup urine disease (MSUD) in Malaysian population

Maple syrup urine disease (MSUD) is a rare autosomal recessive metabolic disorder. This disorder is usually caused by mutations in any one of the genes; BCKDHA, BCKDHB and DBT, which represent E1α, E1β and E2 subunits of the branched-chain α-keto acid dehydrogenase (BCKDH) complex, respectively. This study presents the molecular characterization of 31 MSUD patients. Twenty one mutations including 14 new mutations were identified. The BCKDHB gene was the most commonly affected (45.2%) compared to BCKDHA gene (16.1%) and DBT gene (38.7%). In silico webservers predicted all mutations were disease-causing. In addition, structural evaluation disclosed that all new missenses in BCKDHA, BCKDHB and DBT genes affected stability and formation of E1 and E2 subunits. Majority of the patients had neonatal onset MSUD (26 of 31). Meanwhile, the new mutation; c.1196C > G (p.S399C) in DBT gene was noted to be recurrent and found in 9 patients. Conclusion: Our findings have expanded the mutational spectrum of the MSUD and revealed the genetic heterogeneity among Malaysian MSUD patients. We also discovered the p.S399C from DBT gene was noted as a recurrent mutation in Malay community and it suggested the existence of common and unique mutation in Malay population.

Two novel mutations in the BCKDHB gene that cause maple syrup urine disease

BACKGROUND

Maple syrup urine disease (MSUD) is a rare metabolic disorder of autosomal recessive inheritance caused by decreased activity of branched-chain α-ketoacid dehydrogenase complex (BCKD). Mutations in the three genes (BCKDHA, BCKDHB and DBT) are associated with MSUD. Here, we describe the presenting symptoms, clinical course and gene mutation analysis of a Chinese boy with MSUD.

METHODS

Plasma amino acid analysis was performed by tandem mass spectrometry and the levels of organic acids in urine were measured with gas chromatography-mass spectrometry. The BCKDHB gene was sequenced by Sanger method. Furthermore, the significance of the novel mutations was predicted by Polyphen and Mutationtaster. After diagnosis, the patient was fed with protein-restricted diet to reduce intake of BCAA and was treated with _l-carnitine. Metabolic parameters, clinical presentation and mental development were followed up.

RESULTS

The patient was diagnosed as MSUD. Two novel BCKDHB mutations (c.523 T > C and c.478-25_552del100) were identified. In silico analysis predicted that the two mutations were "disease causing". The boy tolerated the treatment well and had symptomatic improvement. He presented with mild hypotonia and had nearly normal DQ scores at the age of 10 months. The two novel mutations resulted in the clinical manifestations of MSUD. Our results may reflect the heterogeneity of the pathogenic variants found in patients with MSUD.

Silico analysis of a novel mutation c.550delT in a Chinese patient with maple syrup urine disease

Twelve days after birth, the child was admitted to hospital because of "poor response, lethargy, and poor appetite for 6 days" and developed into coma immediately. The ventilator is required. The urine had significant maple syrup odor. After different diagnosis, she was diagnosed with classical maple syrup urine disease.

Clinical characteristics and mutation analysis of five Chinese patients with maple syrup urine disease

Maple syrup urine disease (MSUD) is an autosomal recessive disorder affecting branched-chain amino acids (BCAAs) metabolism and caused by a defect in the thiamine-dependent enzyme branched chain α-ketoacid dehydrogenase (BCKD) with subsequent accumulation of BCAAs and corresponding branched-chain keto acids (BCKAs) metabolites. Presently, at least 4 genes of BCKDHA, BCKDHB, DLD and DBT have been reported to cause MSUD. Furthermore, more than 265 mutations have been identified as the cause across different populations worldwide. Some studies have reported the data of gene mutations in Chinese people with MSUD. In this study, we present clinical characteristics and mutational analyses in five Chinese Han child with MSUD, which had been screened out by tandem mass spectrometry detection of amino acids in blood samples. High-throughput sequencing, Sanger sequence and real-time qualitative PCR were performed to detect and verify the genetic mutations. Six different novel genetic variants were validated in BCKDHB gene and BCKDHA gene, including c.523 T > C, c.659delA, c.550delT, c.863G > A and two gross deletions. Interestingly, 3 cases had identical mutation of BCKDHB gene (c.659delA). We predicted the pathogenicity and analyzed the clinical characteristics. The identification of these mutations in this study further expands the mutation spectrum of MSUD and contributes to prenatal molecular diagnosis of MSUD.

MRI and clinical features of maple syrup urine disease: preliminary results in 10 cases

PURPOSE

We aimed to evaluate the magnetic resonance imaging (MRI) and clinical features of maple syrup urine disease (MSUD).

METHODS

This retrospective study consisted of 10 MSUD patients confirmed by genetic testing. All patients underwent brain MRI. Phenotype, genotype, and areas of brain injury on MRI were retrospectively reviewed.

RESULTS

Six patients (60%) had the classic form of MSUD with BCKDHB mutation, three patients (30%) had the intermittent form (two with BCKDHA mutations and one with DBT mutation), and one patient (10%) had the thiamine-responsive form with DBT mutation. On diffusion-weighted imaging, nine cases presented restricted diffusion in myelinated areas, and one intermittent case with DBT mutation was normal. The classic form of MSUD involved the basal ganglia in six cases; the cerebellum, mesencephalon, pons, and supratentorial area in five cases; and the thalamus in four cases, respectively. The intermittent form involved the cerebellum, pons, and supratentorial area in two cases. The thiamine-responsive form involved the basal ganglia and supratentorial area.

CONCLUSION

Our preliminary results indicate that patients with MSUD presented more commonly in classic form with BCKDHB mutation and displayed extensive brain injury on MRI.

Four novel mutations of the BCKDHA, BCKDHB and DBT genes in Iranian patients with maple syrup urine disease

BACKGROUND

Maple syrup urine disease (MSUD) is a rare metabolic autosomal recessive disorder caused by dysfunction of the branched-chain α-ketoacid dehydrogenase (BCKDH) complex. Mutations in the BCKDHA, BCKDHB and DBT genes are responsible for MSUD. The current study analyzed seven Iranian MSUD patients genetically and explored probable correlations between their genotype and phenotype.

METHODS

The panel of genes, including BCKDHA, BCKDHB and DBT, was evaluated, using routine the polymerase chain reaction (PCR)-sequencing method. In addition, protein modeling (homology and threading modeling) of the deduced novel mutations was performed. The resulting structures were then analyzed, using state-of-the-art bioinformatics tools to better understand the structural and functional effects caused by mutations.

RESULTS

Seven mutations were detected in seven patients, including four novel pathogenic mutations in BCKDHA (c.1198delA, c.629C>T), BCKDHB (c.652C>T) and DBT (c.1150A>G) genes. Molecular modeling of the novel mutations revealed clear changes in the molecular energy levels and stereochemical traits of the modeled proteins, which may be indicative of strong correlations with the functional modifications of the genes. Structural deficiencies were compatible with the observed phenotypes.

CONCLUSIONS

Any type of MSUD can show heterogeneous clinical manifestations in different ethnic groups. Comprehensive molecular investigations would be necessary for differential diagnosis.

Two homozygous mutations in the exon 5 of BCKDHB gene that may cause the classic form of maple syrup urine disease

Maple syrup urine disease (MSUD) is a rare autosomal recessive genetic disorder caused by defects in the catabolism of the branched-chain amino acids (BCAAs). Classic form of MSUD (CMSUD) is caused by mutations in BCKDHA, BCKDHB, DBT genes mostly. In this study, we analyzed the clinical and genetic characteristics of two patients with CMSUD. Two homozygous mutations, c.517G > T (p.Asp173Tyr) and c.503G > A (p.Arg168His), both in the exon 5 of BCKDHB were detected respectively. The novel mutation p.Asp173Tyr of patient A, inherited from his parents, is predicted to affect conformation of protein by computer analysis. The reported mutation p.Arg168His observed in patient B seemed to occur in a maternal uniparental disomy inheritance manner. Review of related literature revealed that most missense mutations in exon 5 of BCKDHB in homozygous genotype often result in CMSUD because of its incorrect conformation, and exon 5 of BCKDHB might be a susceptible region. Thus the novel homozygous mutation p.Asp173Tyr and the founder homozygous mutation p.Arg168His may be responsible for the clinical presentation of the two CMSUD patients, facilitating the future genetic counselling and prenatal diagnosis.

Identification of six novel mutations in Iranian patients with maple syrup urine disease and their in silico analysis

Maple syrup urine disease (MSUD) is a rare inborn error of branched-chain amino acid metabolism. The disease prevalence is higher in populations with elevated rate of consanguineous marriages such as Iran. Different types of disease causing mutations have been previously reported in BCKDHA, BCKDHB, DBT and DLD genes known to be responsible for MSUD phenotype. In this study, two sets of multiplex polymorphic STR (Short Tandem Repeat) markers linked to the above genes were used to aid in homozygosity mapping in order to find probable pathogenic change(s) in the studied families. The families who showed homozygote haplotype for the BCKDHA gene were subsequently sequenced. Our findings showed that exons 2, 4 and 6 contain most of the mutations which are novel. The changes include two single nucleotide deletion (i.e. c. 143delT and c.702delT), one gross deletion covering the whole exon four c.(375+1_376-1)_(8849+1_885-1), two splice site changes (c.1167+1G>T, c. 288+1G>A), and one point mutation (c.731G>A). Computational approaches were used to analyze these two novel mutations in terms of their impact on protein structure. Computational structural modeling indicated that these mutations might affect structural stability and multimeric assembly of branched-chain α-keto acid dehydrogenase complex (BCKDC).

Two novel compound heterozygous mutations in the BCKDHB gene that cause the intermittent form of maple syrup urine disease

Intermittent maple syrup urine disease (MSUD) is a potentially life-threatening metabolic disorder caused by a deficiency of branched chain α-ketoacid dehydrogenase (BCKD) complex. In contrast to classic MSUD, children with the intermittent form usually have an atypical clinical manifestation. Here, we describe the presenting symptoms and clinical course of a Chinese boy with intermittent MSUD. Mutation analysis identified two previously unreported mutations in exon 7 of the BCKDHB gene: c.767A > G (p.Y256C) and c.768C > G (p.Y256X); the parents were each heterozygous for one of these mutations. In silico analysis predicted Y256C probably affects protein structure; Y256X leads to a premature stop codon. This case demonstrates intermittent MSUD should be suspected in cases with symptoms of recurrent encephalopathy, especially ataxia or marked drowsiness, which usually present after the neonatal period and in conjunction with infection. symmetrical basal ganglia damage but normal myelination in the posterior limb will assist differential diagnosis; alloisoleucine is a useful diagnostic marker and mutation analysis may be of prognostic value. These novel mutations Y256C and Y256X result in the clinical manifestation of a variant form of MSUD, expanding the mutation spectrum of this disease.

Evolution of maple syrup urine disease in patients diagnosed by newborn screening versus late diagnosis

Maple syrup urine disease (MSUD) is a rare metabolic disorder for which the newborn screening (NBS) is possible but it has not been yet implemented for most Spanish regions. In the present study, we assess the clinical features and outcome of 14 MSUD Spanish patients with similar treatment protocol diagnosed either by NBS or by clinical symptoms. Eight patients were detected by NBS, four classic and four moderate MSUD. The average age at detection was 4.6 days, the mean plasmatic concentration of leucine at diagnosis was 1807 μM; the average number of days with leucine >1000 μM was 0.7 (0-4) and the mean number of total hospitalizations was 1.6 (0-5). Mean follow-up time was 70 months. They had good evolution: all remain asymptomatic, but 2 patients have attention deficit and hyperactivity disorder. Six patients with late diagnosis of classic MSUD were followed during 41 months. All presented with acute encephalopathy during the first month of life, mean leucine levels of 2355 μM, mean number of days with leucine >1000 μM of 6.6 (1-13) and mean number of total hospitalizations of 5.3 (4-7). Only two patients have a psychomotor development index in the lower limit (80 and 83). For all patients a good genotype-phenotype correlation was found and four novel mutations were identified: p.A311H, p.T84S, p.T397L, pL398P. Our study support that NBS improves prognosis of MSUD patients. But early diagnosis and an aggressive treatment together with a close monitoring of leucine levels improve neurological evolution in MSUD patients, even for those not detected by NBS.

QDPR gene mutation and clinical follow-up in Chinese patients with dihydropteridine reductase deficiency

BACKGROUND

This study aimed to investigate the mutation spectrum of the QDPR gene, to determine the effect of mutations on dihydropteridine reductase (DHPR) structure/function, to discuss the potential genotypephenotype correlation, and to evaluate the clinical outcome of Chinese patients after treatment.

METHODS

Nine DHPR-deficient patients were enrolled in this study and seven of them underwent neonatal screening. QDPR gene mutations were analyzed and confirmed by routine methods. The potential pathogenicity of missense variants was analyzed using Clustal X, PolyPhen program and Swiss-PDB Viewer 4.04_OSX software, respectively. The clinical outcomes of the patients were evaluated after long-term treatment.

RESULTS

In 10 mutations of the 9 patients, 4 were novel mutations (G20V, V86D, G130S and A175R), 4 were reported by us previously, and 2 known mutations were identified. R221X was a hotspot mutation (27.7%) in our patients. Eight missense mutations probably had damage to protein. Six patients in this series were treated with a good control of phenylalanine level. The height and weight of the patients were normal at the age of 4 months to 7.5 years. Four patients, who underwent a neonatal screening and were treated early, showed a normal mental development. In 2 patients diagnosed late, neurological symptoms were significantly improved.

CONCLUSIONS

The mutation spectrum of the QDPR gene is different in the Chinese population. Most mutations are related to severe phenotype. The determination of DHPR activity should be performed in patients with hyperphenylalaninemia. DHPR-deficient patients who were treated below the age of 2 months may have a near normal mental development.

Defects of thiamine transport and metabolism

Thiamine, in the form of thiamine pyrophosphate, is a cofactor for a number of enzymes which play important roles in energy metabolism. Although dietary thiamine deficiency states have long been recognised, it is only relatively recently that inherited defects in thiamine uptake, activation and the attachment of the active cofactor to target enzymes have been described, and the underlying genetic defects identified. Thiamine is transported into cells by two carriers, THTR1 and THTR2, and deficiency of these results in thiamine-responsive megaloblastic anaemia and biotin-responsive basal ganglia disease respectively. Defective synthesis of thiamine pyrophosphate has been found in a small number of patients with episodic ataxia, delayed development and dystonia, while impaired transport of thiamine pyrophosphate into the mitochondrion is associated with Amish lethal microcephaly in most cases. In addition to defects in thiamine uptake and metabolism, patients with pyruvate dehydrogenase deficiency and maple syrup urine disease have been described who have a significant clinical and/or biochemical response to thiamine supplementation. In these patients, an intrinsic structural defect in the target enzymes reduces binding of the cofactor and this can be overcome at high concentrations. In most cases, the clinical and biochemical abnormalities in these conditions are relatively non-specific, and the range of recognised presentations is increasing rapidly at present as new patients are identified, often by genome sequencing. These conditions highlight the value of a trial of thiamine supplementation in patients whose clinical presentation falls within the spectrum of documented cases.

Different gene preferences of maple syrup urine disease in the aboriginal tribes of Taiwan

BACKGROUND

Maple syrup urine disease (MSUD) is a rare inborn error of metabolism caused by a deficiency of the branched-chain α-ketoacid dehydrogenase (BCKD) complex. Mutations in any one of the three different genes encoding for the BCKD components, namely, BCKDHA, BCKDHB, and DBT, may be responsible for this disease. In Taiwan, few MSUD cases were diagnosed clinically, and most of these patients are from Aboriginal tribes.

MATERIALS AND METHODS

To identify and detect the carrier frequency of MSUD in Taiwanese Aboriginal tribes, we performed biochemical and molecular studies from peripheral blood in MSUD patients and dried blood on filter paper in the enrolled screened populations.

RESULTS

Homozygous A208T and I281T of BCKDHA were found in two patients from Hans (non-Aboriginal Taiwanese), respectively; compound heterozygous mutations of the DBT gene [4.7 kb deletion/c.650-651insT (L217F or L217fsX223) and c.650-651insT/c.88-89delAT] were found in two patients from Amis, respectively, after direct DNA sequencing and polymerase chain reaction-restriction fragment length polymorphism studies. There were no cases of deleted 4.7-kb heterozygote out of 302 normal people (Hans, n = 125; Atayal, n = 156; and Saisiyat, n = 21); by contrast, the DBT mutations c.650-651insT and deleted 4.7-kb heterozygote were noted in 2/121 and 1/121, respectively, from the general population of the Amis, a southeastern Taiwanese tribe.

CONCLUSION

Although the Taiwanese Austronesian Aboriginal tribes are considered to share a common origin, different gene preferences of MSUD were noted. The novel DBT mutation c.650-651insT was more prevalent than the deleted 4.7-kb heterozygote in the Amis population. The reported 4.7-kb deletion indicating a possible founder mutation may be preserved in the southern and eastern, but not in northern Aboriginal tribes of Taiwan.

A systematic review and meta-analysis of the association between angiotensin II type 1 receptor A1166C gene polymorphism and myocardial infarction susceptibility

BACKGROUND AND AIM

Many reported studies have been conducted to investigate the association of angiotensin II type 1 receptor (AT1R) A1166C gene polymorphism with myocardial infarction (MI) susceptibility. However, the results from those reports are still conflicting. This meta-analysis was performed to study the relationship between AT1R A1166C gene polymorphism and MI risk.

METHOD

The databases of PubMed, Embase, and Cochrane Library were searched as of 1 March 2012, and eligible investigations were recruited into this meta-analysis.

RESULTS

Eighteen investigations were identified for the analysis of association between AT1R A1166C gene polymorphism and MI risk, 11 in Caucasians, three in Asians, two in Africans, one in the population of Brazil and one in the population of Durban, South Africa . There was a marked association between AT1R C allele and MI susceptibility for overall populations (odds ratio (OR)=1.12, 95% confidence interval (CI): 1.01-1.25, p=0.03), and AT1R AA genotype was associated with a lower risk of MI in overall populations (OR=0.87, 95% CI: 0.78-0.98, p=0.02). However, AT1R A1166C gene polymorphism was not associated with MI risk in the sub-groups of Caucasians, Asians, Africans, Brazil and Durban populations.

CONCLUSIONS

C allele is a risk factor for the MI susceptibility in overall populations, and AA genotype might be a protective factor against the MI risk in overall populations. However, more case-control association investigations on larger, stratified populations are required in the future.