Joannie Hui

Spectrum of mutations in the MECP2 gene in patients with infantile autism and Rett syndrome

Editor—Rett syndrome (RTT, MIM 312750) is a progressive neurological disorder, occurring almost exclusively in females during their first two years of life . RTT is one of the most common causes of mental retardation in females, with an incidence of 1 in 10 000-15 000 female births. Patients with classical RTT appear to develop normally until 6-18 months of age, then gradually lose speech and purposeful hand use, and, eventually, develop microcephaly, seizures, autism, ataxia, hyperventilation, and stereotypic hand movements. After the initial regression, the clinical condition stabilises and patients usually survive into adulthood. Laboratory investigations have not shown any metabolic abnormalities in affected subjects.1 RTT is included in the differential diagnosis of autistic disorder in girls.1-3 Qualitative abnormalities in social and communicative development and stereotypic behaviour are typically present in RTT. Definitive diagnosis is often delayed until after the loss of purposeful hand movements and the relatively characteristic hyperventilation later in childhood,1 and earlier diagnosis would be desirable. The occurrence of a few familial cases with maternal inheritance suggests that RTT is an X linked dominant mutation with lethality in hemizygous males. Previous exclusion mapping studies using RTT families identified a locus in Xq28.4-6 Using a systematic gene screening approach, Amir et al 7and Wan et al 8 have identified mutations in the MECP2 gene, which encodes methyl-CpG binding protein 2, as the cause of some RTT cases. Most of the mutations are de novo and occur at a CpG dinucleotide. The cytosine in the CpG dinucleotide is a frequent site for DNA methylation and deamination of methylated cytosine to thymine causes the transition. The MeCP2 protein silences methylated chromatin by recruiting a histone deacetylase complex.9 Unlike most other transcriptional repressor proteins, however, the binding site of MeCP2 occurs frequently in genomic DNA …

Mutational analysis of 65 Wilson disease patients in Hong Kong Chinese: Identification of 17 novel mutations and its genetic heterogeneity

AbstractWilson disease (WD), an autosomal recessive disorder of copper transport, is the most common inherited liver disorder in Hong Kong Chinese. This was the first local study to elucidate the molecular basis and establish an effective DNA-based diagnostic protocol. The ATP7B genes of 65 patients were amplified by polymerase chain reaction (PCR) and sequenced. Haplotype analysis was performed using D13S301, D13S314, and D13S316. The p.L770L/p.R778L status in 660 subjects was determined to estimate WD prevalence. Allele age of p.R778L was determined by the smallest homozygosity region between D13S301 and D13S270. We identified 42 different mutations with 17 being novel. p.R778L (17.3%) was the most prevalent. Exons 2, 8, 12, 13, and 16 harbored 70% mutations. Thirty-two haplotypes were associated with WD chromosomes. The estimated prevalence rate was 1 in 5,400. Three out of 660 normal subjects had p.L770L/p.R778L. In the remaining 657 individuals, neither p.L770L nor p.R778L was found. We characterized a Hong Kong Chinese-specific ATP7B mutation spectrum with great genetic diversity. Exons 2, 8, 12, 13, and 16 should be screened first. The perfect linkage disequilibrium suggested that p.R778L and its private polymorphism p.L770L originated from a single ancestor. This East-Asian-specific mutation p.R778L/p.L770L is aged at least 5,500 years.

Novel mutations in ETFDH gene in Chinese patients with riboflavin-responsive multiple acyl-CoA dehydrogenase deficiency.

BACKGROUND Multiple acyl-CoA dehydrogenase deficiency (MADD, OMIM 231680) or glutaric aciduria type II (GAII) is an inherited autosomal recessive disease affecting fatty acid, amino acid and choline metabolism, due to mutations in one of three genes namely, electron transfer flavoprotein alpha-subunit, ETFA (OMIM 608053), electron transfer flavoprotein beta-subunit, ETFB (OMIM 130410) and electron transfer flavoprotein dehydrogenase, ETFDH (OMIM 231675). Some MADD patients are responsive to riboflavin treatment with an excellent prognosis. Recently, mutations in ETFDH were found to be responsible for all riboflavin-responsive MADD patients. In this study, we present the clinical features and molecular studies of 2 Chinese families with riboflavin-responsive MADD. METHODS Genomic DNA was extracted from peripheral blood samples or skin fibroblast cultures from the patients and normal controls. The thirteen exons of ETFDH were amplified by PCR. PCR products were sequenced in both forward and reverse directions. To rule out mutations in other genes, phenotype segregation was studied in the families by microsatellite markers in the proximity of the 3 genes, ETFA, ETFB and ETFDH. RESULTS Four novel mutations in ETFDH were detected in the 2 families. In family 1, a frame shift mutation, c.1355delG which introduced a premature-termination codon (PTC), I454X in exon 11 of ETFDH was found. Another mutation was a c.250G>A transition in exon 3 of ETFDH, A84T. In family 2, two novel missense mutations were identified, P137S, in exon 4 and G467R in exon 11. No carrier of these four mutations was identified from about 150 alleles of healthy Chinese control subjects. CONCLUSIONS Four novel mutations (3 missenses and 1 deletion) in ETFDH were found in Chinese families that presented with riboflavin-responsive MADD, which further expands the list of mutations found in patients with riboflavin-responsive MADD. Furthermore, we illustrated the utility of phenotype-genotype segregation in MADD families to prioritize genes for sequencing or to rule out the presence of disease causing mutation in other genes in MADD and other diseases caused by multiple genes.

Risk of Vitamin A Toxicity From Candy-Like Chewable Vitamin Supplements for Children

Numerous vitamin supplements are available over-the-counter to the general public. Some such supplements are available as candy-like chewable preparations to encourage consumption by children. We report 3 cases of overdose of such preparations. Each patient had taken an estimated 200000 to 300000 IU of vitamin A. Their circulating vitamin A (retinol and retinyl palmitate) concentrations were monitored over a 6-month period. There were no clinical or biochemical complications noted. However, there were marked increases in both retinol and retinyl palmitate concentrations above age-related reference ranges. In particular, it took 1 to 3 weeks for the serum retinol concentrations to peak and many months for them to normalize. Parents should be warned about the dangers of excessive vitamin consumption. Clinicians should be aware of the late peak in serum retinol concentrations, which may lead to late complications of vitamin A overdose.

Recurrent and Novel Mutations of GCDH Gene in Chinese Glutaric Acidemia Type I Families

Glutaric acidemia type I is caused by mutations of the glutaryl‐CoA dehydrogenase (GCDH) gene resulting in loss of GCDH enzyme activity. Patients present with progressive dystonia and lesions in basal ganglia. Dietary treatment, when instituted from the early neonatal period, markedly reduces dystonia and morbidity. Early diagnosis and prenatal diagnosis will be facilitated by knowledge of locally prevalent GCDH mutations. Several common GCDH mutations have been found in different ethnic groups. GCDH mutations were studied in 5 Chinese glutaric acidemia type I families. We detected two novel recurrent mutations (A219T and IVS10‐2A>C) which were found in two unrelated families. An asymptomatic carrier of IVS10‐2A>C was also found on screening of 120 individuals. Other mutations were identified, including two other novel (R386G & IVS3+1G>A) and two known mutations (G178R & R355H). Fibroblasts from patients carrying the novel mutations were confirmed to be deficient for GCDH activity. This is the first report of GCDH mutations describing recurrent mutations in Chinese patients. The carrier rate of IVS10‐2A>C may be particularly high in Chinese.

Expanding phenotype and clinical analysis of tyrosine hydroxylase deficiency

This study included 12 Chinese patients with a wide spectrum of phenotypes of tyrosine hydroxylase deficiency. Seven females and 5 males, aged 2.2 to 41 years, had phenotypes ranging from severe type with onset at infancy to mild type with onset after 3 years of age. Patients with the severe type had encephalopathy with poor treatment response or infantile parkinsonism with motor delay. Patients with the less common mild type had dopa-responsive dystonia or a newly recognized predominant symptom of myopathy. Female siblings had more severe phenotypes. The phenotype and treatment outcomes were strongly related to a homovanillic acid level and homovanillic acid/5-hydroxyindolacetic acid ratio of less than 1 in the cerebrospinal fluid. Hyperprolactinemia was found in 50% of the severe cases. Levodopa was the mainstay of treatment, and early addition of selegiline resulted in a remarkable response in some patients. Treatment response for mild-type patients is universally good even with a treatment delay of 10 years after onset of neurological symptoms.

Mutational and haplotype analysis of AGL in patients with glycogen storage disease type III

AbstractGlycogen storage disease type III (GSD III) is a rare autosomal recessive inherited disorder caused by a deficiency of the glycogen-debranching enzyme (AGL). We investigated two GSD III patients and identified four different mutations. Nucleotide sequence analysis revealed patient 1 of Chinese descent to be a compound heterozygote for a novel nonsense mutation, R34X, and the splicing mutation (IVS32−12A > G) reported in a Japanese patient. Patient 2 of Japanese origin was found to be compound heterozygous for a novel nonsense mutation, Y1148X, and the splicing mutation (IVS14+1G > T) that we had described previously. To determine whether splicing mutations occurred independently, we performed intense AGL haplotype analysis using 21 intragenic polymorphic markers plus a novel polymorphism IVS32−97 A/G in the vicinity of the IVS32 splicing mutation. Patient 1 of Chinese origin and the Japanese patient homozygous for the IVS32−12A > G were found to have different haplotypes, indicating the IVS32−12A > G mutation to be a recurrent mutation. This is the first recurrent mutation established by intense haplotyping in the AGL gene.

Overview of common inherited metabolic diseases in a Southern Chinese population of Hong Kong

BACKGROUND The Joint metabolic clinic at the Prince of Wales Hospital was established in January 1997 to provide a comprehensive multi-disciplinary care to patients with inherited metabolic diseases (IMDs). Patients are referred from both within and outside our hospital. Until July, 2000, more than 40 patients and families with 20 different biochemical diagnoses attend the clinic for regular follow up. A pattern of more common IMDs among Hong Kong Chinese emerged from our case registry. In order to advance the understanding of Chinese metabolic diseases, we examined the molecular basis of those diseases with unique features in Chinese or were locally prevalent. Mutations were found in patients with primary carnitine deficiency, ornithine transcarbamylase deficiency, X-linked adrenoleukodystrophy, glutaric aciduria type I, and galactosemia. We also analyzed the mutations in multiple carboxylase deficiency and Niemann-pick type C on four families. CONCLUSIONS Although IMDs are a significant cause of mortality and morbidity among pediatric patients, with a better understanding of the molecular genetics of these diseases, prenatal diagnosis of these common IMDs will be facilitated, which is currently the most effective way of controlling IMDs.

A novel mutation (G233D) in the glycogen phosphorylase gene in a patient with hepatic glycogen storage disease and residual enzyme activity.

We identified a novel mutation in the glycogen phosphorylase gene (PGYL) in a Chinese patient with glycogen storage disease (GSD) type VI. The patient presented with gross hepatomegaly since the age of two without history of any hypoglycemic attack. Otherwise, he was largely asymptomatic. Liver tissue enzyme assays revealed a mild deficiency of total glycogen phosphorylase. Both PGYL and PHKA2 genes were sequenced. The patient was homozygous of a missense mutation G233D in PGYL. This location forms a hairpin turn secondary structure and the small glycine residue is completely conserved in all the orthologous proteins from Escherichia coli to mammals. This is the sixth reported mutation of this form of GSD.

A genomic approach to mutation analysis of holocarboxylase synthetase gene in three Chinese patients with late-onset holocarboxylase synthetase deficiency

OBJECTIVE Multiple carboxylase deficiency (MCD, MIM:253270) is a common organic aciduria and caused by deficiency of either biotinidase or holocarboxylase synthetase (HLCS; EC 6.3.4.10). Patients commonly present during early infancy with acute metabolic derangements and severe metabolic acidosis. Recently, a late onset form of HLCS deficiency was also described. The different phenotypes (early and late presenting) may be related to a spectrum of mutations in HLCS gene. Applications of mutation analysis in HLCS had been limited previously by the requirement of cDNA from living tissue for study. We described here a genomic approach for molecular diagnosis of HLCS deficiency which we have used to detect mutations in Chinese patients who had the late-onset form of HLCS deficiency. In addition, a fibroblast cell line with MCD from Coriell Cell repositories was also studied. DESIGN AND METHODS Three Chinese patients with late onset HLCS deficiency were studied. The genomic sequence of HLCS was retrieved and newly designed primers were used to cover all coding sequences of the gene. PCR products were analyzed by direct sequencing. Population allelic frequencies of mutations detected were determined by genotyping of control samples by restriction fragment length polymorphism. RESULTS We found a recurrent mutation, R508W, in the three unrelated Chinese patients. Two were homozygous for this mutation. The other patient was a compound heterozygote of R508W and a novel mutation, D634N. The results suggest that R508W may be an important and relatively prevalent disease-causing mutation in Chinese MCD patients. A fibroblast cell-line from an African patient revealed an additional novel mutation, R565X and a known mutation, V550M. CONCLUSION R508W is a recurrent mutation in Chinese MCD patients which is associated with the late onset phenotype. This new genomic approach for mutation analysis of HLCS gene provides new opportunities in studies of MCD.