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.

Circulating thyrotropin receptor messenger ribonucleic acid is not an effective marker in the follow-up of differentiated thyroid carcinoma.

BACKGROUND: Circulating thyrotropin receptor messenger ribonucleic acid (TSHR mRNA) assay has been validated in the follow-up of differentiated thyroid carcinoma (DTC) because of its high sensitivity during thyroid hormone therapy and no interference with endogenous anti-thyroglobulin antibodies (TgAb) compared to serum thyroglobulin (Tg). We investigated the efficacy of TSHR mRNA assay in 160 DTC patients using quantitative PCR (qPCR). FINDINGS: Only TSHR mRNA level of structural persistent disease with TgAb-positive (3.47 (2.97-9.53) pg equivalents/µg total RNA; p = 0.013) and its subgroup of distant metastasis patients with TgAb-positive (5.55 (3.28-12.52) pg equivalents/µg total RNA; p = 0.009) were significantly different from patients with no evidence of disease (2.32 (1.44-3.94) pg equivalents/µg total RNA). Applying cutoff at 2.00 pg equivalents/µg total RNA enabled us to predict structural persistent disease patients with a sensitivity of 62.3 % and a specificity of 42.9 %. Although, the sensitivity of TSHR mRNA assay in TgAb-postive patients (88.2 %) was superior than serum Tg (47.1 %) (p = 0.00002), the accuracy of the test is only 54.5 %. CONCLUSIONS: This study demonstrated that TSHR mRNA assay has good sensitivity in TgAb-positive patients but it is neither specific enough as a first-line of testing nor a surrogate marker in the follow-up of our DTC patients.

A newly identified locus for benign adult familial myoclonic epilepsy on chromosome 3q26.32-3q28.

Benign Adult Familial Myoclonic Epilepsy (BAFME) is an autosomal dominant disorder characterized by adult-onset cortical tremor or action myoclonus predominantly in the upper limbs, and generalized seizures. We investigated a Thai BAFME family. Clinical and electrophysiological studies revealed that 13 were affected with BAFME. There were a total of 24 individuals studied. Genetic analysis by genome-wide linkage study (GWLS) was performed using 400 microsatellite markers and excluded linkage of the previous BAFME loci, 8q23.3-q24.1, and 2p11.1-q12.2. GWLS showed that the disease-associated region in our Thai family was linked to a newly identified locus on chromosome 3q26.32-3q28. This locus represents the fourth chromosomal region for BAFME.

PTPRF is disrupted in a patient with syndromic amastia.

BACKGROUND: The presence of mammary glands distinguishes mammals from other organisms. Despite significant advances in defining the signaling pathways responsible for mammary gland development in mice, our understanding of human mammary gland development remains rudimentary. Here, we identified a woman with bilateral amastia, ectodermal dysplasia and unilateral renal agenesis. She was found to have a chromosomal balanced translocation, 46,XX,t(1;20)(p34.1;q13.13). In addition to characterization of her clinical and cytogenetic features, we successfully identified the interrupted gene and studied its consequences. METHODS: Characterization of the breakpoints was performed by molecular cytogenetic techniques. The interrupted gene was further analyzed using quantitative real-time PCR and western blotting. Mutation analysis and high-density SNP array were carried out in order to find a pathogenic mutation. Allele segregations were obtained by haplotype analysis. RESULTS: We enabled to identify its breakpoint on chromosome 1 interrupting the protein tyrosine receptor type F gene (PTPRF). While the patient's mother and sisters also harbored the translocated chromosome, their non-translocated chromosomes 1 were different from that of the patient. Although a definite pathogenic mutation on the paternal allele could not be identified, PTPRF's RNA and protein of the patient were significantly less than those of her unaffected family members. CONCLUSIONS: Although ptprf has been shown to involve in murine mammary gland development, no evidence has incorporated PTPRF in human organ development. We, for the first time, demonstrated the possible association of PTPRF with syndromic amastia, making it a prime candidate to investigate for its spatial and temporal roles in human breast development.

A novel p.E276K IDUA mutation decreasing α-L-iduronidase activity causes mucopolysaccharidosis type I.

PURPOSE: To characterize the pathogenic mutations causing mucopolysaccharidosis type I (MPS I) in two Thai patients: one with Hurler syndrome (MPS IH), the most severe form, and the other with Scheie syndrome (MPS IS), the mildest. Both presented with distinctive phenotype including corneal clouding. METHODS: The entire coding regions of the α-L-iduronidase (IDUA) gene were amplified by PCR and sequenced. Functional characterization of the mutant IDUA was determined by transient transfection of the construct into COS-7 cells. RESULTS: Mutation analyses revealed that the MPS IH patient was homozygous for a previously reported mutation, c.252insC, while the MPS IS patient was found to harbor a novel c.826G>A (p.E276K) mutation. The novel p.E276K mutation was not detected in 100 unaffected ethnic-matched control chromosomes. In addition, the glutamic acid residue at codon 276 was located at a well conserved residue. Transient transfection of the p.E276K construct revealed a significant reduction of IDUA activity compared to that of the wild-type IDUA suggesting it as a disease-causing mutation. CONCLUSIONS: This study reports a novel mutation, expanding the mutational spectrum for MPS I.

PKHD1 sequence variations in 78 children and adults with autosomal recessive polycystic kidney disease and congenital hepatic fibrosis.

PKHD1, the gene mutated in autosomal recessive polycystic kidney disease (ARPKD)/congenital hepatic fibrosis (CHF), is an exceptionally large and complicated gene that consists of 86 exons and has a number of alternatively spliced transcripts. Its longest open reading frame contains 67 exons that encode a 4074 amino acid protein called fibrocystin or polyductin. The phenotypes caused by PKHD1 mutations are similarly complicated, ranging from perinatally-fatal PKD to CHF presenting in adulthood with mild kidney disease. To date, more than 300 mutations have been described throughout PKHD1. Most reported cohorts include a large proportion of perinatal-onset ARPKD patients; mutation detection rates vary between 42% and 87%. Here we report PKHD1 sequencing results on 78 ARPKD/CHF patients from 68 families. Differing from previous investigations, our study required survival beyond 6 months and included many adults with a CHF-predominant phenotype. We identified 77 PKHD1 variants (41 novel) including 19 truncating, 55 missense, 2 splice, and 1 small in-frame deletion. Using computer-based prediction tools (GVGD, PolyPhen, SNAP), we achieved a mutation detection rate of 79%, ranging from 63% in the CHF-predominant group to 82% in the remaining families. Prediction of the pathogenicity of missense variants will remain challenging until a functional assay is available. In the meantime, use of PKHD1 sequencing data for clinical decisions requires caution, especially when only novel or rare missense variants are identified.

Novel mutations in the STK11 gene in Thai patients with Peutz-Jeghers syndrome.

Peutz-Jeghers syndrome (PJS), a rare autosomal dominant inherited disorder, is characterized by hamartomatous gastrointestinal polyps and mucocutaneous pigmentation. Patients with this syndrome have a predisposition to a variety of cancers in multiple organs. Mutations in the serine/threonine kinase 11 (STK11) gene have been identified as a major cause of PJS. Here we present the clinical and molecular findings of two unrelated Thai individuals with PJS. Mutation analysis by Polymerase Chain Reaction-sequencing of the entire coding region of STK11 revealed two potentially pathogenic mutations. One harbored a single nucleotide deletion (c.182delG) in exon 1 resulting in a frameshift leading to premature termination at codon 63 (p.Gly61AlafsX63). The other carried an in-frame 9-base-pair (bp) deletion in exon 7, c.907_915del9 (p.Ile303_Gln305del). Both deletions were de novo and have never been previously described. This study has expanded the genotypic spectrum of the STK11 gene.

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.

A novel mutation in EFNB1, probably with a dominant negative effect, underlying craniofrontonasal syndrome.

Craniofrontonasal syndrome (CFNS) is an X-linked disorder whose main clinical manifestations include coronal craniosynostosis and frontonasal dysplasia. Very recently, CFNS was shown to be caused by mutations in EFNB1 encoding ephrin-B1, and 20 mutations have been described. We report a Thai woman with CFNS, in whom a novel mutation was discovered: c.685_686insG, in exon 5 of EFNB1. It is the first insertion and the most 3' point mutation in EFNB1 reported to date. The mutation is expected to result in a truncated ephrin-B1 of 230 amino acids, composed of a nearly complete extracellular part of ephrin-B1 with no transmembrane and cytoplasmic domains. This truncated protein might become a soluble form of the ligand, which previously was shown to be able to bind to receptors, but fail to cluster and to activate them--in other words, acting as a dominant negative protein. Nonetheless, further studies to detect the protein are needed to substantiate the hypothesis.