Clinical and molecular characterization of Thai patients with Wiskott-Aldrich syndrome.

Wiskott-Aldrich syndrome (WAS) is an X-linked recessive primary immunodeficiency disorder caused by mutations in the gene encoding the WAS protein (WASP). Classic WAS is characterized by thrombocytopenia with small-sized platelets, recurrent infections, eczema and increased susceptibility to autoimmune diseases and haematologic malignancies. Here, we reported on seven unrelated Thai individuals with classic WAS. In addition to clinical and immunologic characterization, mutation analysis by PCR-sequencing the entire coding region of WASP was performed. Recurrent and novel mutations were successfully identified. A nonsense mutation, the c.55C>T (p.Q19X), has not been previously described, expanding the mutational spectrum of WASP. The patient with this newly described mutation developed cow's milk allergy manifesting as angioedema and urticaria and had cytomegalovirus infection that was successfully treated with long-term ganciclovir. This study reported long-term follow-up of seven patients with molecular confirmation of WAS and infrequent features in the patient with classic WAS carrying the novel nonsense mutation.

Pathogenic mechanism of mutations in the thyroid hormone receptor ß gene.

BACKGROUND: Resistance to thyroid hormone (RTH) is characterized by a variable degree of reduced tissue sensitivity to thyroid hormone (TH). It is usually caused by mutations in the TH receptor-ß (TRß) gene. AIMS: To characterize clinical and molecular features of a Thai patient with RTH. Functional significance of the identified mutation as well as other uncharacterized TRß mutations was also investigated. MATERIALS AND METHODS: Exons 3-10 of the TRß gene were assessed by PCR-sequencing. Functional characterization of the mutant TRß was determined by the luciferase reporter system. RESULTS: A mutation in exon 9 of the TRß gene resulting in a methionine to threonine substitution at codon 313 was identified. The functional consequence of this mutation and other uncharacterized known mutations (p.I276L, p.I280S, p.L330S, p.G344A, p.M442T) was evaluated by transfection studies. Four out of 6 had a significant impairment of T3-dependent transactivation. When co-transfected with the wild-type TRß, all exhibited a dominant negative effect. CONCLUSION: A de novo mutation was identified in the patient with clinical diagnosis of RTH. Our findings provide a strong support that interfering with the T3-mediated transcriptional activation of the wild-type TRß independent of the ability to activate transcription is a major pathogenic mechanism causing RTH.

Holocarboxylase synthetase deficiency: novel clinical and molecular findings.

Multiple carboxylase deficiency (MCD) is an autosomal recessive metabolic disorder caused by defective activity of biotinidase or holocarboxylase synthetase (HLCS) in the biotin cycle. Clinical symptoms include skin lesions and severe metabolic acidosis. Here, we reported four unrelated Thai patients with MCD, diagnosed by urine organic acid analysis. Unlike Caucasians, which biotinidase deficiency has been found to be more common, all of our four Thai patients were affected by HLCS deficiency. Instead of the generally recommended high dose of biotin, our patients were given biotin at 1.2 mg/day. This low-dose biotin significantly improved their clinical symptoms and stabilized the metabolic state on long-term follow-up. Mutation analysis by polymerase chain reaction-sequencing of the entire coding region of the HLCS gene revealed the c.1522C>T (p.R508W) mutation in six of the eight mutant alleles. This suggests it as the most common mutation in the Thai population, which paves the way for a rapid and unsophisticated diagnostic method for the ethnic Thai. Haplotype analysis revealed that the c.1522C>T was on three different haplotypes suggesting that it was recurrent, not caused by a founder effect. In addition, a novel mutation, c.1513G>C (p.G505R), was identified, expanding the mutational spectrum of this gene.

Prenatal diagnosis of a novel mutation, c.529C>T (p.Q177X), in the BCKDHA gene in a family with maple syrup urine disease.

Maple syrup urine disease (MSUD) is an autosomal recessive metabolic disorder caused by defective activity of the branched-chain alpha-keto-acid dehydrogenase (BCKD) complex. The disease-causing mutations can affect the BCKDHA, BCKDHB or DBT genes encoding for the E1a, E1b, and E2 subunits, respectively, of the BCKD complex. Here we report a girl who first presented to our clinic at 4 years of age with profound mental retardation. A diagnosis of MSUD was subsequently made based on the results of plasma amino acid analysis. Mutation analysis confirmed that she was homozygous for a novel mutation, c.529C>T (p.Q177X) in BCKDHA, while both parents, who were first cousins, were heterozygous. This enabled us to give an option of prenatal diagnosis to the parents. The prenatal testing for MSUD was performed during the mother's subsequent pregnancy and revealed that the fetus was heterozygous for the mutation. The healthy male neonate was born and his genotype was tested by restriction enzyme analysis, which confirmed the result of the prenatal testing. In summary, a late diagnosis of MSUD in patients without an unusual odour could occur especially in countries without neonatal screening programs as seen in the index patient. Mutation detection was, however, still beneficial to the family since prenatal testing could be performed in subsequent pregnancies. In addition, a novel mutation was found, expanding the mutation spectrum of this disease.

Study of the poliovirus receptor related-1 gene in Thai patients with non-syndromic cleft lip with or without cleft palate.

Non-syndromic cleft lip with or without cleft palate (CL/P) has a complex etiology with several genetic and environmental factors playing a role. The poliovirus receptor related-1 gene (PVRL1) has been shown to underlie a syndromic form of CL/P and, in some populations, contribute to non-syndromic CL/P. To investigate whether mutations in PVRL1 play a part in the formation of non-syndromic CL/P in the Thai population, 100CL/P patients were analyzed for mutations in PVRL1 by polymerase chain reaction amplification and direct sequencing of all the coding regions of its alpha isoform. Of this series of patients, one was found to be heterozygous for 1183G>A in exon 6, expected to result in the substitution of a valine by a methionine at position 395 (V395M). This mutation was not found in 200 unaffected Thai control individuals. The valine position is conserved across all known mammalian PVRL1 sequences. In conclusion, a novel non-synonymous PVRL1 mutation was found in a Thai patient with non-syndromic CL/P, suggesting a possible etiologic role of PVRL1 in non-syndromic CL/P across different populations.

TBX22 mutations are a frequent cause of non-syndromic cleft palate in the Thai population.

Mutations in the TBX22 gene underlie an X-linked malformation syndrome with cleft palate (CP) and ankyloglossia. Its mutations also result in non-syndromic CP in some populations. To investigate whether mutations in TBX22 play a part in the formation of non-syndromic CP in the Thai population, we performed mutation analysis covering all the coding regions of the TBX22 gene in 53 unrelated Thai patients with non-syndromic CP. We identified four potentially pathogenic mutations, 359G-->A (R120Q), 452G-->T (R151L), 1166C-->A (P389Q), and 1252delG in four different patients. All mutations were not detected in at least 112 unaffected ethnic-matched control chromosomes and had never been previously reported. R120Q and R151L, found in two sporadic cases, were located in the DNA binding T-box domain. P389Q and 1252delG, found in two familial cases, were at the carboxy-terminal region, which has never been described. Our study indicates that TBX22 mutations are responsible for a significant proportion of Thai non-syndromic CP cases confirming its importance as a frequent cause of non-syndromic CP across different populations.

Expanding the phenotypic spectrum of Caffey disease.

Infantile cortical hyperostosis (ICH) is an inherited disorder characterized by hyperirritability, acute inflammation of soft tissues, and massive subperiosteal new bone formation. It typically appears in early infancy and is considered a benign self-limiting disease. We report a three-generation Thai family with ICH, the oldest being a 75-year-old man. A heterozygous mutation for a 3040C-->T in exon 41 of COL1A1 was found in affected individuals, further confirming the autosomal dominance of Caffey disease that is caused by this particular mutation. The novel findings in our studies include short stature and persistent bony deformities in the elderly. The height mean Z-score of the five affected individuals was -1.75, compared to 0.53 of the other seven unaffected individuals giving a p-value of 0.008. Short stature may be partly due to progressive height loss from scoliosis, compression fractures of the spine and genu varus. These features, which have not previously been described, expand the phenotypic spectrum of the Caffey disease.

Two novel frameshift mutations of the EBP gene in two unrelated Thai girls with Conradi-Hünermann-Happle syndrome.

Conradi-Hünermann-Happle syndrome, also known as X-linked dominant chondrodysplasia punctata (CDPX2), is characterized by skeletal abnormalities, cutaneous anomalies and cataracts. CDPX2 is caused by mutations in the emopamil-binding protein (EBP). We report two unrelated Thai female patients with clinically typical CDPX2, in which we discovered two novel and de novo frameshift mutations: 506-507delAG and 540-541delCC. This study demonstrates that EBP is the gene responsible for CDPX2 across different populations and extends the total number of confirmed mutations to 55.

De novo missense mutation, S541Y, in the p63 gene underlying Rapp-Hodgkin ectodermal dysplasia syndrome.

Rapp-Hodgkin syndrome (RHS) is an autosomal dominant disorder characterized by ectodermal dysplasia and cleft lip/cleft palate. Very recently, mutations in p63 have been identified as a cause of RHS; to date five such mutations have been identified. We describe a Thai girl with RHS. She had short stature, ectodermal dysplasia, epiphora, cleft lip, cleft palate, and normal development. Mutation analysis for the entire coding region of p63 identified a novel and de novo mutation, 1622C--> A (S541Y), in the SAM domain, predicting an abnormal alpha tail of the p63alpha protein isotypes. This observation supports that majority of patients with RHS are caused by mutations affecting the tail of p63alpha, a region that also contains most of the pathogenic mutations in ankyloblepharon-ectodermal dysplasia-clefting (AEC) syndrome.