Xiao-jie Xu

Two novel mutations in TMEM38B result in rare autosomal recessive osteogenesis imperfecta.

Osteogenesis imperfecta (OI) is a group of clinically and genetically heterogeneous disorders characterized by decreased bone mass and recurrent bone fractures. Transmembrane protein 38B (TMEM38B) gene encodes trimeric intracellular cation channel type B (TRIC-B), mutations of which will lead to the rare form of autosomal recessive OI. Here we detected pathogenic gene mutations in TMEM38B and investigated its phenotypes in three children with OI from two non-consanguineous families of Chinese Han origin. The patients suffered from recurrent fractures, low bone mass, mild bone deformities and growth retardation, but did not have impaired hearing or dentinogenesis imperfecta. Next-generation sequencing and Sanger sequencing revealed a homozygous novel acceptor splice site variant (c.455-7T>G in intron 3, p.R151_G152insVL) in family 1 and a homozygous novel nonsense variant (c.507G>A in exon 4, p.W169X) in family 2. The parents of the probands were all heterozygous carriers of these mutations. We reported the phenotype and novel mutations in TMEM38B of OI for the first time in Chinese population. Our findings of the novel mutations in TMEM38B expand the pathogenic spectrum of OI and strengthen the role of TRIC-B in the pathogenesis of OI.

Genotype-phenotype analysis of a rare type of osteogenesis imperfecta in four Chinese families with WNT1 mutations.

BACKGROUNDS Osteogenesis imperfecta (OI) is a rare inherited disease characterized by increased bone fragility and vulnerability to fractures. Recently, WNT1 is identified as a new candidate gene for OI, here we detect pathogenic mutations in WNT1 and analyze the genotype-phenotype association in four Chinese families with OI. METHODS We designed a targeted next generation sequencing panel with known fourteen OI-related genes. We applied the approach to detect pathogenic mutations in OI patients and confirmed the mutations with Sanger sequencing and cosegregation analysis. Clinical fractures, bone mineral density (BMD) and the other clinical manifestations were evaluated. We also observed the effects of bisphosphonates in OI patients with WNT1 mutations. RESULTS Four compound heterozygous mutations (c.110T>C; c.505 G>T; c. 385G>A; c.506 G>A) in WNT1 were detected in three unrelated families. These four mutations had not been reported yet. A recurrent homozygous mutation (c.506dupG) was identified in the other two families. These patients had moderate to severe OI, white to blue sclera, absence of dentinogenesis imperfecta and no brain malformation. We did not observe clear genotype-phenotype correlation in WNT1 mutated OI patients. Though bisphosphonates increased BMD in WNT1 related OI patients, height did not increase and fracture continued. CONCLUSIONS We reported four novel heterozygous variants and confirmed a previous reported WNT1 mutation in four Chinese families with a clinical diagnosis of OI. Our study expanded OI spectrum and confirmed moderate to severe bone fragility induced by WNT1 defects.

SOST polymorphisms and response to alendronate treatment in postmenopausal Chinese women with osteoporosis

AIM To investigate the association between SOST gene polymorphisms and response to alendronate treatment. MATERIALS & METHODS 639 Chinese postmenopausal women with osteoporosis or osteopenia received alendronate treatment. Polymorphisms of SOST were analyzed. Bone mineral density (BMD), serum ALP and β-CTX levels were measured. The correlation of SOST polymorphisms with changes of BMD and bone biomarkers after treatment was analyzed. RESULTS rs1234612 and rs851054 polymorphisms were correlated to baseline lumbar spine BMD (p < 0.05). After 12 months of treatment rs1234612 and rs865429 polymorphisms were correlated to BMD changes at the lumbar spine (p < 0.05) or femoral neck (p < 0.05), respectively. CONCLUSION The polymorphisms of SOST are genetic factors affecting bone health and response to alendronate in Chinese postmenopausal women.

Recurrent and novel mutations in the NTRK1 gene lead to rare congenital insensitivity to pain with anhidrosis in two Chinese patients

BACKGROUND Congenital insensitivity to pain with anhidrosis (CIPA) is an extremely rare autosomal recessive autonomic and sensory neuropathy. CIPA is associated with various mutations in NTRK1. CASES Two unrelated Chinese patients presented separately with symptoms of insensitivity to pain, inability to sweat, repeated painless fractures, and Charcot arthropathy were recruited. Both of them were clinically diagnosed with CIPA. Increased serum bone resorption marker (β-CTX) levels and decreased BMD were observed in both patients. X-ray films revealed enlarged bony calli in the fracture sites, Charcot arthropathy, and bilateral lower limb osteomyelitis. Sanger sequencing demonstrated compound heterozygous mutations in NTRK1 for proband 1 (IVS7-33T>A in intron 7 and c. 2281C>T in exon 17) and for proband 2 (IVS7-33T>A in intron 7 and c.1652delA in exon 14), of which the variation in exon 14 in NTRK1 was a novel mutation. CONCLUSIONS We report the detailed phenotypes, as well as both recurrent and novel mutations in NTRK1 in 2 Chinese patients with CIPA. The genetic findings of our study expand the gene mutation spectrum of CIPA.

Novel mutations in FKBP10 in Chinese patients with osteogenesis imperfecta and their treatment with zoledronic acid

Osteogenesis imperfecta (OI) is a group of hereditary disorders characterized by decreased bone mass and increased fracture risk. The majority of OI cases have an autosomal dominant pattern of inheritance and are usually caused by mutations in genes encoding type I collagen. OI cases of autosomal recessive inheritance are rare, and OI type XI is attributable to mutation of the FKBP10 gene. Here, we used next-generation sequencing and Sanger sequencing to detect mutations in FKBP10 and to analyze their relation to the phenotypes of OI type XI in three Chinese patients. We also evaluated the efficacy of zoledronic acid treatment in these patients. Two of the affected patients had novel compound heterozygous mutations, one patient with c.343C>T (p.R115X) in exon 2 and c.1085delC (p.A362fsX1) in exon 7, and the other patient with c.879C>G (p.Y293X) in exon 5 and c.918-3C>G in intron 5. In the third proband, we identified a homozygous single base-pair duplication, c.831dupC (p.G278RfsX95) in exon 5. In conclusion, we report for the first time that these novel pathogenic mutations of FKBP10 can lead to the extremely rare type XI OI without contractures, which expands the genotypic spectrum of OI. The phenotypes of these patients are similar to patients with types III or IV OI, and zoledronic acid is effective in increasing BMD, inhibiting bone resorption biomarkers and reducing fractures of these patients.

The analysis of DKK1 polymorphisms in relation to skeletal phenotypes and bone response to alendronate treatment in Chinese postmenopausal women.

AIM To investigate the correlation between DKK1 polymorphisms with bone phenotypes and response to alendronate treatment. MATERIALS & METHODS Five tag single nucleotide polymorphisms of DKK1 were analyzed in 639 Chinese postmenopausal women with osteoporosis or osteopenia. Bone mineral density (BMD), β-CTX and ALP were measured before and after alendronate treatment. RESULTS Genotypes at rs1896367, rs1528877 and rs2241529 correlated to baseline BMD (p < 0.05). rs1528877 and rs2241529 polymorphisms correlated to baseline β-CTX levels (p < 0.05). rs2241529 polymorphisms of DKK1 had a small influence on the skeletal response to alendronate treatment (p < 0.05). CONCLUSION DKK1 polymorphisms may correlate to baseline BMD and serum β-CTX levels, but present a weak effect on the response to alendronate.

A cryptic balanced translocation involving COL1A2 gene disruption cause a rare type of osteogenesis imperfecta

BACKGROUND Osteogenesis imperfecta (OI) is a group of hereditary disorders characterized by low bone mass and recurrent fractures. Most OI cases follow an autosomal dominant pattern of inheritance and are attributed to mutations in genes encoding type I collagen (COL1A1/COL1A2). Genomic structural variations involving type I collagen genes are extremely rare in OI. CASE REPORT In this study, we characterized a de novo balanced translocation of t(5;7)(q32;q21.3) that caused an extremely rare type of OI in a patient from a non-consanguineous family. The clinical phenotypes of this OI included recurrent fractures, low bone mass, macrocephaly, blue sclera and failure to thrive. Next-generation sequencing was used to identify the translocation, and Sanger sequencing was used to validate and map the breakpoints. The breakpoint on chromosome 7 disrupted the COL1A2 gene in the 17th exon, presumed to affect type I collagen production and give rise to OI. The breakpoint on chromosome 5 disrupted the protein phosphatase 2 regulatory subunit B, beta gene (PPP2R2B) within the first intron. CONCLUSIONS This is the first report of a copy-neutral structural variant involving COL1A2 that leads to a rare type of OI. This study expands the genotypic spectrum of OI and demonstrates the effectiveness of targeted sequencing for breakpoint mapping.

Novel Mutations in PLOD2 Cause Rare Bruck Syndrome

Bruck syndrome is a rare autosomal recessive form of osteogenesis imperfecta (OI), which is mainly characterized by joint contractures and recurrent fragility fractures. Mutations in FKBP10 and PLOD2 were identified as the underlying genetic defects of Bruck syndrome. Here we investigated the phenotypes and the pathogenic mutations of three unrelated Chinese patients with Bruck syndrome. Clinical fractures, bone mineral density (BMD), bone turnover biomarkers, and skeletal images were evaluated in detail. The pathogenic mutations were identified by targeted next-generation sequencing and subsequently confirmed by Sanger sequencing and cosegregation analysis. We also evaluated the effects of zoledronic acid on bone fracture incidence and BMD of the patients. Three patients had congenital joint contractures, recurrent fragility fractures, camptodactyly, clubfoot, scoliosis, but without dentinogenesis imperfecta and hearing loss. Five novel heterozygous mutations were detected in PLOD2, including three heterozygous missense mutations (c.1138C>T, p.Arg380Cys; c.1153T>C, p.Cys385Arg; and c.1982G>A, p.Gly661Asp), one heterozygous nonsense mutation (c.2038C>T, p.Arg680X), and one heterozygous splice-site mutation (c.503-2A>G). Their parents were all heterozygous carriers of these mutations in PLOD2. No clear genotype–phenotype correlations were found in these patients with PLOD2 mutations. Z-score of BMD was significantly increased, but scoliosis progressed and new bone fractures occurred during the treatment of zoledronic acid. Our findings expanded the spectrum of gene mutations of Bruck syndrome.

THE CLINICAL CHARACTERISTICS AND EFFICACY OF BISPHOSPHONATES IN AUDLT PATIENTS WITH OSTEOGENESIS IMPERGECTA

OBJECTIVE Osteogenesis imperfecta (OI) is characterized by low bone mass and recurrent fractures. Adults with OI are often treated with oral or intravenous bisphosphonates (BPs). We investigated the clinical phenotypes of adult OI patients and prospectively compared the efficacy of oral alendronate (ALN) with intravenous zoledronic acid (ZOL) in OI patients. METHODS This 24-month, observational, randomized clinical study included 60 adult patients with OI. We compared the differences in bone mineral density (BMD) and bone turnover biomarkers between OI adults and healthy subjects. Thereafter, OI patients were randomized at a 2:1 ratio to receive either weekly oral ALN 70 mg or once-yearly infusion of ZOL 5 mg. The efficacy outcomes were changes in BMD, bone turnover biomarkers, and fracture incidence. RESULTS Adult OI patients had significantly lower BMD and significantly higher cross-linked C-telopeptide of type I collagen (β-CTX) levels than age-/sex-/BMI-matched healthy subjects. A total of 52 patients completed the 24-month clinical study. BMD at lumbar spine, femoral neck, and total hip were equivalently elevated in the ALN (10.5, 13.2, and 14.7%, respectively) and ZOL (11.3, 13.7, and 11.7%, respectively; all P>.05) groups. Serum alkaline phosphatase decreased by 30.3% in the ALN group and 37.3% in the ZOL group (P = .12), and β-CTX decreased by 58.0% in the ALN group and 63.6% in the ZOL group (P = .48). Compared to the prior fracture rates, clinical fracture incidences were decreased in the ALN and ZOL groups (both P<.05). CONCLUSION Adults with OI present significantly lower bone mass and higher bone resorption biomarkers than healthy populations. Oral ALN and intravenous ZOL are equally effective at increasing BMD and inhibiting bone turnover in adults with OI. The treatment may reduce fractures in this study, but further efforts are still needed to demonstrate the anti-fracture efficacy of BPs. ABBREVIATIONS 25OHD = 25-hydroxyvitamin D ALN = alendronate ALP = alkaline phosphatase BMD = bone mineral density BMI = body mass index BP = bisphosphonate β-CTX = cross-linked C-telopeptide of type I collagen FN = femoral neck LS = lumbar spine OI = osteogenesis imperfecta RCT = randomized controlled trial TH = total hip ZOL = zoledronic acid.

A novel mutation in CLDN16 results in rare familial hypomagnesaemia with hypercalciuria and nephrocalcinosis in a Chinese family

BACKGROUND Familial hypomagnesaemia with hypercalciuria and nephrocalcinosis (FHHNC) is a rare autosomal recessively inherited disease characterized by excessive wasting of renal tubular magnesium and calcium. FHHNC is associated with various mutations in CLDN16 and CLDN19. CASES Two children from a consanguineous family of Chinese Han origin demonstrated manifestations of rickets, polyuria, polydipsia, hematuria and failure to thrive. Hypomagnesaemia (0.49-0.50mmol/L), hypercalciuria or a trend to hypercalciuria (24hour urine calcium: 3.8-5.1mg/kg/day), and secondary hyperparathyroidism (serum PTH level: 94.7-200pg/mL) were revealed upon laboratory examination. Using targeted next-generation sequencing and subsequent confirmation by Sanger sequencing, a novel homozygous mutation was identified in the CLDN16 gene of both FHHNC patients. This specific mutation, a 16bp deletion followed by a 23bp insertion in exon 3, led to the generation of a premature termination codon. The parents and an unaffected sister were all heterozygous carriers of this mutation. CONCLUSIONS We detected a novel mutation in CLDN16 for the first time. The clinical and genetic findings from this study will help to expand the understanding of this rare disease, FHHNC.