S. Balcells

Large-scale analysis of association between polymorphisms in the transforming growth factor beta 1 gene (TGFB1) and osteoporosis : The GENOMOS study

INTRODUCTION The TGFB1 gene which encodes transforming growth factor beta 1, is a strong candidate for susceptibility to osteoporosis and several studies have reported associations between bone mineral density (BMD), osteoporotic fractures and polymorphisms of TGFB1, although these studies have yielded conflicting results. METHODS We investigated associations between TGFB1 polymorphisms and BMD and fracture in the GENOMOS study: a prospective multicenter study involving 10 European research studies including a total of 28,924 participants. Genotyping was conducted for known TGFB1 polymorphisms at the following sites: G-1639-A (G-800-A, rs1800468), C-1348-T (C-509-T, rs1800469), T29-C (Leu10Pro, rs1982073), G74-C (Arg25Pro, rs1800471) and C788-T (Thr263Ile, rs1800472). These polymorphisms were genotyped prospectively and methodology was standardized across research centers. Genotypes and haplotypes were related to BMD at the lumbar sine and femoral neck and fractures. RESULTS There were no significant differences in either women or men at either skeletal site for any of the examined polymorphisms with the possible exception of a weak association with reduced BMD (-12 mg/cm2) in men with the T-1348 allele (p<0.05). None of the haplotypes was associated with BMD and none of the polymorphisms or haplotypes significantly affected overall risk of fractures, however, the odds ratio for incident vertebral fracture in carriers of the rare T788 allele was 1.64 (95% CI: 1.09-2.64), p<0.05. CONCLUSIONS This study indicates that polymorphic variation in the TGFB1 gene does not play a major role in regulating BMD or susceptibility to fractures. The weak associations we observed between the C-1348-T and lumbar spine BMD in men and between C788-T and risk of incident vertebral fractures are of interest but could be chance findings and will need replication in future studies.

Polymorphisms in the interleukin-6 receptor gene are associated with bone mineral density and body mass index in Spanish postmenopausal women

OBJECTIVE Osteoporosis and obesity are complex diseases with a strong genetic component. Bone mineral density (BMD) and body mass index (BMI) linkage studies identified a locus at 1q21-23, where the interleukin-6 receptor (IL6R) gene is located. The IL6R and the gp130 receptors are the mediators of IL6 action. Serum levels of IL6 and sIL6R (the soluble form of IL6R) are higher in several diseases such as osteoporosis or obesity. Variants at IL6R have been associated with BMI and obesity. However, IL6R is an as-yet-unexplored osteoporosis candidate gene. DESIGN In the present study we analysed two polymorphisms in the IL6R promoter, -1435 C/T (rs3887104) and -208 G/A (rs4845617), and the Asp358Ala polymorphism (rs8192284), in relation to both BMD and BMI in a cohort of 559 postmenopausal Spanish women. RESULTS The promoter polymorphisms, -1435 C/T and -208 G/A were associated with femoral neck (FN) BMD (P=0.011 and P=0.025 respectively). The C-A and T-G promoter haplotypes were also associated with FN BMD. Additionally, the Asp358Ala variant was associated with lumbar spine BMD (P=0.038). Finally, the -208 G/A polymorphism and the C-G and C-A haplotypes were associated with BMI and obesity, where GG was the risk genotype (P=0.033 for BMI; P=0.010 for obesity). CONCLUSION These data suggest that variants in the IL6R gene are not only involved in the determination of BMI but also relevant for the determination of BMD. The IL6R gene may belong to the growing list of genes known to be involved in both phenotypes.

A new autosomal recessive retinitis pigmentosa locus maps on chromosome 2q31-q33.

Autosomal recessive retinitis pigmentosa (ARRP) is a genetically heterogeneous disease. To date, mutations in four members of the phototransduction cascade have been implicated in ARRP. Additionally, linkage of the disease to three loci on 1p, 1q, and 6p has been described. However, the majority of cases are still uncharacterised. We have performed linkage analysis in a large nuclear ARRP family with five affected sibs. After exclusion of several regions of the genome known to contain loci for retinal dystrophies, a genomic search for linkage to ARRP was undertaken. Positive lod scores were obtained with markers on 2q31-q33 (Zmax at theta = 0.00 of 4.03, 4.12, and 4.12 at D2S364, D2S118, and D2S389, respectively) defining an interval of about 7 cM for this new ARRP locus, between D2S148 and D2S161. Forty-four out of 47 additional ARRP families, tested with markers on 2q32, failed to show linkage, providing evidence of further genetic heterogeneity.

Frequency of the arylsulphatase A pseudodeficiency allele in the Spanish population

Chabás A, Castellvi S, Bayés M, Balcells S, Grinberg D, Vilageliu L1, Marfany G, Lissens W, Gonzàlez‐Duarte R. Frequency of the arylsulphatase A pseudodeficiency allele in the Spanish population. Clin Genet 1993: 44: 320–323.

Mutations in the EXT1 and EXT2 genes in Spanish patients with multiple osteochondromas

Multiple osteochondromas is an autosomal dominant skeletal disorder characterized by the formation of multiple cartilage-capped tumours. Two causal genes have been identified, EXT1 and EXT2, which account for 65% and 30% of cases, respectively. We have undertaken a mutation analysis of the EXT1 and EXT2 genes in 39 unrelated Spanish patients, most of them with moderate phenotype, and looked for genotype-phenotype correlations. We found the mutant allele in 37 patients, 29 in EXT1 and 8 in EXT2. Five of the EXT1 mutations were deletions identified by MLPA. Two cases of mosaicism were documented. We detected a lower number of exostoses in patients with missense mutation versus other kinds of mutations. In conclusion, we found a mutation in EXT1 or in EXT2 in 95% of the Spanish patients. Eighteen of the mutations were novel.

Autosomal recessive retinitis pigmentosa in Spain: evaluation of four genes and two loci involved in the disease

Autosomal recessive retinitis pigmentosa (ARRP) is a genetically heterogeneous form of retinal degeneration. The genes for the β‐subunit of rod phosphodiesterase (PDEB), rhodopsin (RHO), peripherin/RDS (RDS) and the rod outer segment membrane protein 1 (ROM1), as well as loci at 6p and 1q, have previously been reported as the cause of ARRP. In order to determine whether they are responsible for the disease in Spanish pedigrees, linkage and homozygosity studies using markers at these loci were carried out on 47 Spanish ARRP families. SSCP analysis was performed to search for mutations in the genes cosegregating with the disease in particular pedigrees. Three homozygous mutations in the PDEB gene were found, thus accounting for 6% of the cases. No other disease‐causing mutation was observed in the other genes analysed, nor was significant evidence found for the involvement of the loci at 6p or 1q. On the basis of these data, it is unlikely that these genes and loci account for a considerable proportion of ARRP cases.

Novel homozygous mutation in the alpha subunit of the rod cGMP gated channel (CNGA1) in two Spanish sibs affected with autosomal recessive retinitis pigmentosa

Retinitis pigmentosa (RP, MIM 268000) comprises a clinically and genetically heterogeneous group of disorders leading to progressive dysfunction of the rod photoreceptors of the retina. Patients suffer early night blindness followed by loss of peripheral vision associated with pigment accumulation in the outer retina and attenuation of the retinal vessels. The pathophysiology of RP involves apoptosis of rod cells. Although macular vision is preserved in the initial stages of the disease, visual field defects gradually increase and cone affectation follows. RP can be inherited as an autosomal dominant, autosomal recessive, digenic, or X linked trait. Several RP genes and loci have been described to date (RetNet web site: http://utsph.sph.uth.tmc.edu/www/Wtsph/RetNet/home.htm). Altogether, the genes known to cause the autosomal recessive forms explain a small proportion of cases, while the great majority remain unexplained, which illustrates the extreme genetic heterogeneity of this condition. As expected, many of the ARRP genes are rod specific, some are only expressed in the retinal pigment epithelium, and none is cone specific. Cyclic nucleotide gated channels (CNCG) are a group of non-selective ion channels present in different tissues. The rod cGMP gated cation channel is located in the outer segment of the plasma membrane and is involved in the last step of the phototransduction cascade. In spite of a similar function, rod and cone cells express different CNCG genes.1 Rod channels are predicted to form heterotetramers of two alpha and beta subunit dimers. Each contains a core structural unit of six membrane spanning segments, a pore region, and a cGMP binding domain. The alpha peptide ( CNGA1 , MIM 123825, GDB 127557) forms a functional channel by itself and is considered the main functional subunit, while the beta counterpart ( CNGB1, MIM 600724, GDB 434397) modulates the activity of the channel and is unable to promote ion transfer by …

Molecular characterization of five patients with homocystinuria due to severe methylenetetrahydrofolate reductase deficiency

Urreizti R, Moya‐García AA, Pino‐ Ángeles A, Cozar M, Langkilde A, Fanhoe U, Esteves C, Arribas J, Vilaseca MA, Pérez‐Dueñas B, Pineda M, González V, Artuch R, Baldellou, A, Vilarinho L, Fowler B, Ribes A, Sánchez‐Jiménez F, Grinberg D, Balcells S. Molecular characterization of five patients with homocystinuria due to severe MTHFR deficiency.

A broad spectrum of genomic changes in latinamerican patients with EXT1/EXT2-CDG

Multiple osteochondromatosis (MO), or EXT1/EXT2-CDG, is an autosomal dominant O-linked glycosylation disorder characterized by the formation of multiple cartilage-capped tumors (osteochondromas). In contrast, solitary osteochondroma (SO) is a non-hereditary condition. EXT1 and EXT2, are tumor suppressor genes that encode glycosyltransferases involved in heparan sulfate elongation. We present the clinical and molecular analysis of 33 unrelated Latin American patients (27 MO and 6 SO). Sixty-three percent of all MO cases presented severe phenotype and two malignant transformations to chondrosarcoma (7%). We found the mutant allele in 78% of MO patients. Ten mutations were novel. The disease-causing mutations remained unknown in 22% of the MO patients and in all SO patients. No second mutational hit was detected in the DNA of the secondary chondrosarcoma from a patient who carried a nonsense EXT1 mutation. Neither EXT1 nor EXT2 protein could be detected in this sample. This is the first Latin American research program on EXT1/EXT2-CDG.