Novel mutations of TCIRG1 cause a malignant and mild phenotype of autosomal recessive osteopetrosis (ARO) in four Chinese families.

Human autosomal recessive osteopetrosis (ARO), also known as infantile malignant osteopetrosis, is a rare genetic bone disorder that often causes death. Mutations in T-cell immune regulator 1 (TCIRG1) are a frequent cause of human ARO. Six additional genes (TNFSF11, TNFRSF11A, CLCN7, OSTM1, SNX10, PLEKHM1) were also found to be associated with human ARO. In order to expand the mutation spectrum and clinical diversity for a better understanding of the ARO phenotype and to further investigate the clinical characteristics of benign subjects with ARO, we here report five individuals with ARO from four unrelated Chinese families. X-ray examination was conducted and bone turnover markers were assayed. The gene of T-cell immune regulator 1 (TCIRG1) was screened and analyzed. Monocyte-induced osteoclasts were prepared and their resorption ability was studied in vitro. We identified five novel mutations (c.66delC, c.1020+1_1020+5dup, c.2181C>A, c.2236+6T>G, c.692delA) in these patients. Four patients displayed a malignant phenotype, three of them died, and one who received bone marrow transplantation survived. The remaining one, a 24-year-old male from a consanguineous family, was diagnosed based on radiological findings but presented no neurological or hematological defects. He was homozygous for c.2236+6T>G in intron 18; this mutation influenced the splicing process. An in vitro functional study of this novel splicing defect showed no resorption pits on dentine slices. TCIRG1-dependent osteopetrosis with a mild clinical course was observed for the first time in Chinese population. The present findings add to the wide range of phenotypes of Chinese patients with TCIRG1-dependent ARO and enrich the database of TCIRG1 mutations.

Targeted resequencing of phosphorus metabolism­related genes in 86 patients with hypophosphatemic rickets/osteomalacia.

Hypophosphatemic rickets/osteomalacia is characterized by defective renal phosphate reabsorption and abnormal bone mineralization. Hypophosphatemic rickets/osteomalacia consists of inherited and acquired forms, many of which have unknown aetiology. In the present study, next­generation sequencing­based resequencing was used on samples from Chinese subjects with hypophosphatemic rickets/osteomalacia, aiming to detect the spectrum of pathogenic genes in these patients. A total of 86 hypophosphatemic rickets/osteomalacia patients (ranging from 3 to 70 years old) were recruited. Patients with tumour­induced osteomalacia (TIO), renal tubular acidosis, renal osteodystrophy, and adefovir­induced Fanconi syndrome were excluded. Targeted massively parallel resequencing of 196 candidate genes for hypophosphatemic rickets/osteomalacia was performed in the 86 affected unrelated individuals (cases) and in 100 unrelated healthy controls to identify new genes and mutations in known genes that cause hypophosphatemic rickets/osteomalacia. The results identified seven phosphate­regulating gene with homologies to endopeptidases on the X chromosome (PHEX) mutations (of which two were novel) and one novel dentin matrix protein 1 (DMP1) mutation in eight patients. Following targeted exome sequencing data analysis, 14 candidate disease­related gene loci were selected, two of which were of most concern regarding disease severity. Further validation of the present results is warranted, with additional sequencing projects and functional tests. To our knowledge, the present study is the largest cohort of cases with hypophosphatemic rickets/osteomalacia to undergo targeted resequencing. The diagnosis and understanding of the molecular aetiologies of these disorders will be improved by this fast and efficient approach.

Clinical characteristics and the identification of novel mutations of COL1A1 and COL1A2 in 61 Chinese patients with osteogenesis imperfecta.

Osteogenesis imperfecta (OI) is an inherited connective tissue disorder characterized by brittle bone fractures. The aim of the present study was to investigate the pathogenic gene mutation spectrum and clinical manifestations of mutations in collagen type I, alpha 1 (COL1A1) and collagen type I, alpha 2 (COL1A2) genes in Chinese patients with OI. A total of 61 unrelated Chinese OI patients with COL1A1 and COL1A2 mutations were recruited. All the exons and the exon-intron boundaries of the COL1A1 and COL1A2 genes were amplified and directly sequenced and lumbar spine bone mineral density was measured by dual­energy X­ray absorptiometry. The mutations of the 61 probands included 33 missense mutations, 8 nonsense mutations, 7 splicing variants and 13 frameshift mutations in COL1A1 and COL1A2 genes. A total of 25 novel mutations were identified, including 18 in COL1A1 and 7 in COL1A2. The mutations p.Gly257Arg, p.Gly767Ser and p.Gly821Ser in COL1A1 and p.Gly337Ser in COL1A2 may be located at a mutation hotspot for human OI due to the high repetition rate in OI patients. Family history was positive for OI in 33 probands (54%). All probands had suffered fractures and the most common fracture site was the femur. A total of 49 probands presented with blue sclerae (80.3%), 20 probands suffered from dentinogenesis imperfecta (32.8%) and 1 patient had hearing loss (1.6%). These findings may improve understanding of the pathogenic gene mutation spectrum and the clinical manifestations of mutations of COL1A1 and COL1A2 genes in Chinese patients with OI.

The A242T mutation in the low-density lipoprotein receptor-related protein 5 gene in one Chinese family with osteosclerosis.

OBJECTIVE: Osteosclerosis (OMIM: 144750) is a type of autosomal dominant bone disease caused by a mutation in the low-density lipoprotein receptor-related protein 5 (LRP5) gene. The case of a Chinese family with two affected individuals is reported in the present study in order to investigate the clinical characteristics and virulence genes of this sclerosing bone disorder. METHODS: Biochemical and radiographic examinations and bone mineral density (BMD) and genetic analyses were performed in two patients and eight other family members. RESULTS: The 40-year-old proband (II-1) and her 64-year-old mother (I-2) both had chronic lumbodorsal pain, an elongated mandible and torus palatinus in the center of the hard palate. No fractures were observed in any of the family members. Skull, mandibular and pelvic X-rays in each of the two patients revealed thickened cranial plates, an enlarged sella turcica, an elongated mandible and cortical thickening of the long bones. The BMD values of the two patients was significantly higher than the standard age- and sex-matched adult mean reference values. Both patients had higher serum sclerostin levels, while their renal function markers and serum calcium, phosphonium, parathyroid hormone (PTH) and 25(OH)D levels were within the normal ranges. The heterozygous missense mutation p.Ala242Thr in exon 4 of the LRP5 gene was detected in the two patients, while the other family members and 200 healthy donors had normal wild-type genotypes. CONCLUSION: The A242T mutation in the LRP5 gene resulted in a high bone mass phenotype with an elongated mandible and torus palatinus in this osteosclerotic family.

Identification of one novel mutation in the EVC2 gene in a Chinese family with Ellis-van Creveld syndrome.

Ellis-van Creveld syndrome (EvC) is a rare autosomal recessive skeletal dysplasia characterized by short limbs, short ribs, postaxial polydactyly, and dysplastic nails and teeth. It is caused by biallelic mutations in the EVC or EVC2 gene. Here, we identified a novel nonsense mutation p.W828X (c.2484G>A) in exon 14 and a recurrent nonsense mutation p. R399X (c.1195C>T) in exon 10 of EVC2 gene in a Chinese boy with EvC. Identification of a novel genotype in EvC will provide clues to the phenotype-genotype relations and may assist not only in the clinical diagnosis of EvC but also in the interpretation of genetic information used for prenatal diagnosis and genetic counseling.