Abstract

Cartilage hair hypoplasia (CHH; MIM 250250) is an autosomal recessive disease with diverse clinical manifestations. It is caused by mutations in RMRP gene, the RNA component of the ribonucleoprotein complex RNase MRP. Mutations in RMRP have been found in patients in the core promoter region or in the transcribed region, but the pathogenetic effect of the mutations is unclear. Real-time PCR assays confirmed that both promoter (c.−16_−1 dup and c.−15_+2 dup) and transcribed mutations (c.168G > A and c.218A > G) lower the expression level of RMRP. Experiments with 5′RACE, showed that the reduced transcription in the promoter mutants was accompanied by shifting of the transcription initiation sites to nucleotides 5′-upstream of the authentic site. Low levels of RMRP expression levels with transcript mutations were also seen when constructs encoding the wild-type and mutant genes were transfected into cultured cells. The reduced transcription was correlated with greater instability of mutant RMRP transcripts compared to controls. A comparable reduction was seen when a mouse gene containing the c.70A > G mutation (the major mutation in humans with CHH) was introduced into ES cells in place of one of the wild-type alleles. The low expression level of the c.70A > G Rmrp RNA was confirmed by expression assays into cultured cells, and was again correlated with RNA instability. Our results indicate that a loss of mutant RNA transcripts is a critical feature of pathogenesis. © 2007 Wiley-Liss, Inc.

Multiple epiphyseal dysplasia (MED) is among the most genetically heterogeneous skeletal dysplasias. Six genes involved in MED, COMP, MATN3, COL9A1, COL9A2, COL9A3, and DTDST have been identified; however, the presence of additional disease genes has been reported, and the detection rate for mutations in known genes accounts for no more than 50% of patients with MED in Western populations. Here, we screened the six known disease genes in 35 consecutive Japanese MED patients. We analyzed the entire coding region of each gene, along with flanking intron–exon junctions, by direct sequencing. A total of 19 mutations were identified in COMP, MATN3, COL9A2, COL9A3, and DTDST. The detection rate for known mutations was higher in this study than in previous reports, and we identified a substantially different spectrum of mutations. Mutations in MATN3 were more prevalent among these Japanese patients, whereas no DTDST mutations were detected. Most of the mutations were localized within specific regions of each gene: COMP mutations were found in the calmodulin-like repeat domains; MATN3 mutations in the von Willebrand factor type A domain; and type IX collagen gene mutations occurred in the third collagenous domains. Based on the integration of clinical and genetic information, we propose an algorithm for detecting mutations in Japanese MED patients. Our study further supports the existence of additional MED gene(s). © 2006 Wiley-Liss, Inc.

Diastrophic dysplasia sulfate transporter (DTDST) is a sulfate transporter required for the synthesis of sulfated proteoglycans in the cartilage. Over 30 mutations have been described in the DTDST gene, which result in a continuous clinical spectrum of recessively inherited chondrodysplasias, including, in order of increasing severity, a recessive form of multiple epiphyseal dysplasia (rMED), diastrophic dysplasia (DTD), atelosteogenesis type II (AO-II) and achondrogenesis 1B (ACG-1B). Correlation between disease severity and residual sulfate transport activity has been reported. Here we report a patient with DTDST mutations, whose manifestations fell in a range between AO-II and DTD. The patient was a compound heterozygote for the recurrent c.835C>T (p.R279W) and novel c.1987G>A (p.G663R) mutations. Immunocytochemical analysis in HEK293 cells showed that the p.G663R mutation was localized within the cytoplasm, and not to the cell membrane, suggesting p.G663R is a loss-of-function mutation. Our case supports the previously described correlation between the severity of the phenotype and the putative level of residual transport function. © 2006 Wiley-Liss, Inc.

Multiple epiphyseal dysplasia (MED) is a common skeletal dysplasia characterized by mild to moderate short stature, early-onset of osteoarthritis (OA) mainly in the hip and knee joints, and abnormally small and/or irregular epiphyses. MED is clinically and genetically heterogeneous. Six causative genes of MED have been reported, including type IX collagen genes (COL9A1, COL9A2, COL9A3). All the type IX collagen mutations previously reported cause exon skipping that loses the COL3 domain. Here we have identified a novel COL9A3 mutation co-segregating in a three-generation family with MED. The mutation (IVS3 + 5G > A) was speculated to lose the COL3 domain by skipping of exon 3, which was confirmed by in vitro analysis. The patients were of normal height and had minimal complaints with phenotypes being more severe in male patients. The radiographic phenotypes of the patients were relatively milder than those of previously reported cases, and were indistinguishable to common, idiopathic OA. © 2004 Wiley-Liss, Inc.

Mutations in the gene encoding cartilage oligomeric matrix protein (COMP) cause two common skeletal dysplasias, pseudoachondroplasia (PSACH) and multiple epiphyseal dysplasia (MED). At present, diagnosis of these diseases is based primarily on clinical and radiographic findings and is sometimes erroneous, particularly in adult patients. However, genetic diagnosis is difficult, because COMP mutations are scattered throughout the gene and five additional disease genes for MED exist. There is evidence that circulating COMP may serve as a molecular indicator of a variety of diseases affecting cartilage. Therefore, we investigated plasma COMP concentrations in 21 patients with PSACH or MED. Of these, six PSACH and seven MED patients carried COMP mutations, and the remaining eight MED patients lacked mutations in COMP. We observed significantly decreased plasma COMP levels in patients with COMP mutations compared with controls (P < 0.0001). In addition, plasma COMP levels were significantly decreased in MED patients carrying mutations in COMP relative to those who lacked COMP mutations (P = 0.001). Our results indicate that circulating COMP levels reflect genetic abnormalities in COMP, providing an easier, more rapid and cost-efficient method for diagnosing PSACH and particularly for MED. © 2004 Wiley-Liss, Inc.

We examined 12 Japanese patients with metaphyseal chondrodysplasia (MCD) for mutations in the ribonuclease mitochondrial RNA processing gene (RMRP), and identified four novel mutations in two patients with typical and atypical cartilage-hair hypoplasia (CHH), a form of MCD characterized by extra-skeletal manifestations including hypoplastic hair and defective immunity. A patient with typical CHH had a 17-bp duplication at +3 and a de novo 182G > A. The other patient with atypical CHH had a 17-bp insertion at −20 and a 218A > G. Expression analysis revealed that the allele with this insertion mutation in the promoter region silenced the gene. Spectrum analysis of the mutations and polymorphisms in RMRP showed marked difference between the Japanese and other ethnic groups. Such ethnic and phenotypic difference should be taken into account in mutation analysis of the gene. © 2003 Wiley-Liss, Inc.

Pseudoachondroplasia (PSACH) is a common skeletal dysplasia characterized by disproportionate short stature, early-onset osteoarthrosis, and dysplasia of the spine, epiphysis, and metaphysis. Multiple epiphyseal dysplasia (MED) is a similar but less severe disorder characterized by dysplasia of the epiphysis. Both disorders are caused by mutations in the cartilage oligomeric matrix protein (COMP) gene. COMP mutations cluster in a region of the gene that encodes calmodulin-like repeats (CLRs) and correlate closely with disease severity. Typically, mutations in exon 13 that composes the seventh CLR produce severe PSACH phenotypes, whereas mutations found elsewhere in the gene produce mild PSACH or MED phenotypes. We have identified a PSACH patient carrying a novel mutation in exon 18 of COMP that composes the C-terminal globular domain. This mutation produced a severe PSACH phenotype with marked short stature and deformities of the spine and extremities. Our results extend the range of disease-causing mutations within the COMP gene and demonstrate the importance of the additional domain of COMP protein in its in vivo function. © 2001 Wiley-Liss, Inc.

Chondrodysplasia punctata (CDP) is a heterogeneous group of skeletal dysplasias characterized by stippled epiphyses. A subtype of CDP, X-linked dominant chondrodysplasia punctata (CDPX2), known also as Conradi-Hünermann-Happle syndrome, is a rare skeletal dysplasia characterized by short stature, craniofacial defects, cataracts, ichthyosis, coarse hair, and alopecia. The cause of CDPX2 was unknown until recent identification of mutations in the gene encoding Δ⁸,Δ⁷ sterol isomerase emopamil-binding protein (EBP). Twelve different EBP mutations have been reported in 14 patients with CDPX2 or unclassified CDP, but with no evidence of correlation between phenotype and nature of the mutation. To characterize additional mutations and investigate possible phenotype-genotype correlation, we sequenced the entire EBP gene in 8 Japanese individuals with CDP; 5 of them presented with a CDPX2 phenotypes. We found EBP mutations in all 5 CDPX2 individuals, but none in non-CDPX2 individuals. Three of these CDPX2 individuals carried novel nonsense mutations in EBPand the other two, separate missense mutations that had been reported also in different ethnic groups. Our results, combined with previous information, suggest all EBP mutations that produce truncated proteins result in typical CDPX2, whereas the phenotypes resulted from missense mutations are not always typical for CDPX2. Patients with nonsense mutations showed abnormal sterol profiles consistent with a defect in Δ⁸,Δ⁷ sterol isomerase. X-inactivation patterns of the patients showed no skewing, an observation that supports the assumption that inactivation of the EBP gene occurs at random in affected individuals. Am. J. Med. Genet. 94:300–305, 2000. © 2000 Wiley-Liss, Inc.