Summary Purpose:  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. Methods:  Eighty‐one Thai epileptic patients between 1994 and 2007 from the Chulalongkorn Comprehensive Epilepsy Program were recruited. Thirty‐one subjects had antiepileptic drug (AED)‐induced SJS or MPE (6 CBZ‐SJS, 4 PHT‐SJS, 9 CBZ‐MPE, 12 PHT‐MPE), and 50 were AED‐tolerant controls. Results:  For the first time, a strong association between HLA‐B*1502 and PHT‐induced SJS was found (p = 0.005). A strong association was also found between the HLA‐B*1502 and CBZ‐induced SJS (p = 0.0005), making Thai the first non‐Chinese population demonstrating such an association. Some patients, who were HLA‐B*1502 and suffered from CBZ‐induced SJS, could be tolerant to PHT and vice versa. This suggests that HLA‐B*1502 may be a common attribute required for a Thai patient to develop SJS from these two AEDs; other different elements, however, are also needed for each AED. In addition, no association between HLA‐B alleles and CBZ‐ or PHT‐induced MPE was found. Conclusions:  CBZ‐ and PHT‐induced SJS, but not MPE, is associated with HLA‐B*1502 allele in Thai population.

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.

Previous 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.

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.

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 0 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-valueo0.0001). Of these seven, four were missense mutations in the coding regions and three in the 3 0 UTR. Frequencies of four changes (three in coding, one in 3 0 UTR) were statistically different from those of controls (P-valueo0.05). The c.*34G4A was identified in 1/102 cases and 0/500 controls. This position is conserved in primates and located 10 bp away from a predicted binding site for the miR-140. Luciferase assay revealed that, in the presence of miR-140, the c.*34G4A 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.

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 knock-out 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 acts as an activator 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.

Pfeiffer syndrome (PS) (MIM 101600) is one of the most common syndromic forms of craniosynostosis. It is characterized by craniosysnostosis, midface hypoplasia, broad and medially deviated thumbs, and great toes with partial syndactyly of the digits. Here, we described clinical and genetic features of 12 unrelated Thai individuals with PS. All 12 patients were sporadic, and advanced paternal age was found in 50% of the cases. Polymerase chain reaction sequencing of FGFR1 exon 5 and FGFR2 exons 8, 10, 15, 16, and 17 was performed in all PS patients and revealed 9 recurrent mutations in all patients. Most of the mutations clustered in exons 8 and 10 (9/12) accounting for 75% of PS cases. The most frequently detected mutation, p.S351C, was associated with the severe form of PS in the Thai population. Less frequent mutations in exons 16 (p.K641R) and 17 (p.G663E) were also identified. In addition, the p.P252R mutation in FGFR1 was detected in 1 PS patient with unilateral coronal craniosynostosis expanding the phenotypic spectrum of PS with this particular mutation. Knowing the mutation spectrum of the responsible genes could lead to the most effective strategy in identifying mutations causing Pfeiffer syndrome in the Thai population.

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.