Siraprapa Tongkobpetch

Carbamazepine and phenytoin induced Stevens‐Johnson syndrome is associated with HLA‐B*1502 allele in Thai population

Purpose:u2002 Previous studies found a strong association between HLA‐B*1502 and carbamazepine (CBZ)‐induced Stevens‐Johnson syndrome (SJS) in Han Chinese, but not in Caucasian populations. Even in Han Chinese, the HLA‐B*1502 was not associated with CBZ‐induced maculopapular eruptions (MPE). This study seeks to identify whether HLA‐B*1502 is associated with CBZ‐ or phenytoin (PHT)‐induced SJS or MPE in a Thai population.

MSX1 mutations contribute to nonsyndromic cleft lip in a Thai population

AbstractPrevious studies observed that MSX1 mutations could contribute to nonsyndromic cleft lip with or without cleft palate (CL/P) in some populations. Of the proposed pathogenic mutations, the P147Q variant was predominant in Vietnamese and present in Filipino populations. We investigated whether MSX1 mutations also contribute to nonsyndromic CL/P in the Thai population. Specifically, we performed mutation analysis covering all the coding regions of the MSX1 gene for 100 Thai patients with nonsyndromic CL/P. A total of eight variant sites were identified. Six were in coding regions, including four nonsynonymous changes, 101C>G (A34G), 440C>A (P147Q), 799G>T (G267C), and 832C>T (P278S). The G267C and P278S variants were predicted to be “probably damaging” by PolyPhen, changed themselves as potential exonic splicing enhancers for serine/arginine-rich proteins, and were not present in 162 control individuals of Thai ethnic background. Unlike all of the previously reported potential missense mutations in MSX1, these two novel potential mutations were found in exon 2 on the C-terminal side of the homeodomain protein. Moreover, in contrast to previous reports, we found the P147Q variant in 8 out of 100 Thai controls and an association between the variant and CL/P in our population could not be detected, suggesting that it is not pathogenic. Our data support that MSX1 mutations are found in 2% of cases of CL/P and should be considered for genetic counseling implications, but suggest that the P147Q variant is not pathogenic.

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.

MBTPS2 mutations cause defective regulated intramembrane proteolysis in X-linked osteogenesis imperfecta

Osteogenesis imperfecta (OI) is a collagen-related bone dysplasia. We identified an X-linked recessive form of OI caused by defects in MBTPS2, which encodes site-2 metalloprotease (S2P). MBTPS2 missense mutations in two independent kindreds with moderate/severe OI cause substitutions at highly conserved S2P residues. Mutant S2P has normal stability, but impaired functioning in regulated intramembrane proteolysis (RIP) of OASIS, ATF6 and SREBP transcription factors, consistent with decreased proband secretion of type I collagen. Further, hydroxylation of the collagen lysine residue (K87) critical for crosslinking is reduced in proband bone tissue, consistent with decreased lysyl hydroxylase 1 in proband osteoblasts. Reduced collagen crosslinks presumptively undermine bone strength. Also, proband osteoblasts have broadly defective differentiation. These mutations provide evidence that RIP plays a fundamental role in normal bone development.

PDGFRa mutations in humans with isolated cleft palate

Isolated cleft palate (CP) is common in humans and has complex genetic etiologies. Many genes have been found to contribute to CP, but the full spectrum of genes remains unknown. PCR-sequencing of the entire coding regions and the 3′ untranslated region (UTR) of the platelet-derived growth factor receptor alpha (PDGFRa) and the microRNA (miR), miR-140 identified seven novel single base-pair substitutions in the PDGFRa in 9/102 patients with CP (8.8%), compared with 5/500 ethnic-matched unaffected controls (1%) (the two-tailed P-value<0.0001). Of these seven, four were missense mutations in the coding regions and three in the 3′UTR. Frequencies of four changes (three in coding, one in 3′UTR) were statistically different from those of controls (P-value<0.05). The c.*34G>A was identified in 1/102 cases and 0/500 controls. This position is conserved in primates and located 10u2009bp away from a predicted binding site for the miR-140. Luciferase assay revealed that, in the presence of miR-140, the c.*34G>A significantly repressed luciferase activity compared with that of the wild type, suggesting functional significance of this variant. This is the first study providing evidence supporting a role of PDGFRa in human CP.

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.

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 α tail of the p63α protein isotypes. This observation supports that majority of patients with RHS are caused by mutations affecting the tail of p63α, a region that also contains most of the pathogenic mutations in ankyloblepharon‐ectodermal dysplasia‐clefting (AEC) syndrome.

Disorders with similar clinical phenotypes reveal underlying genetic interaction: SATB2 acts as an activator of the UPF3B gene

Two syndromic cognitive impairment disorders have very similar craniofacial dysmorphisms. One is caused by mutations of SATB2, a transcription regulator and the other by heterozygous mutations leading to premature stop codons in UPF3B, encoding a member of the nonsense-mediated mRNA decay complex. Here we demonstrate that the products of these two causative genes function in the same pathway. We show that the SATB2 nonsense mutation in our patient leads to a truncated protein that localizes to the nucleus, forms a dimer with wild-type SATB2 and interferes with its normal activity. This suggests that the SATB2 nonsense mutation has a dominant negative effect. The patient’s leukocytes had significantly decreased UPF3B mRNA compared to controls. This effect was replicated both in vitro, where siRNA knockdown of SATB2 in HEK293 cells resulted in decreased UPF3B expression, and in vivo, where embryonic tissue of Satb2 knockout mice showed significantly decreased Upf3b expression. Furthermore, chromatin immunoprecipitation demonstrates that SATB2 binds to the UPF3B promoter, and a luciferase reporter assay confirmed that SATB2 expression significantly activates gene transcription using the UPF3B promoter. These findings indicate that SATB2 activates UPF3B expression through binding to its promoter. This study emphasizes the value of recognizing disorders with similar clinical phenotypes to explore underlying mechanisms of genetic interaction.

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.

Two novel EBP mutations in Conradi-Hünermann-Happle syndrome

Conradi-Hünermann-Happle syndrome, also known as chondrodysplasia punctata type 2 (CDPX2), is an X-linked dominant disorder characterized by skin defects, skeletal and ocular abnormalities. CDPX2 was shown to be caused by mutations in the gene encoding emopamil binding protein (EBP). At least 58 different mutations have been described. Here we present clinical and molecular findings in two unrelated Thai girls with CDPX2. Mutation analysis by PCR-sequencing the entire coding region of EBP successfully revealed two potentially pathogenic, novel mutations, c.616G-->T and c.382delC. This study has expanded the spectrum of the EBP gene mutations causing CDPX2.