Edited by: M. Noda Keywords: CD44 Osteoporosis Linkage Alternative splicing RNA In a previous linkage study, suggestive linkage to osteoporosis was observed in marker D11S1392 on chromosome 11p12. The CD44 gene, found at this locus, was sequenced in one of the families studied. Sequencing all coding regions and promoter in affected and non-affected family members revealed a number of sequence variants, one of which was found to be linked and inherited identical by descent together with the linked STR allele. This G to A variant, which does not cause an amino acid change, was found in exon 9 of the CD44 gene, 32 base pairs upstream from the exon-intron junction. Preliminary analysis using a bioinformatics tool suggested that the presence of the A allele abolished an exon splicing enhancer (ESE) site, thus possibly affecting RNA splicing. It was observed using an exon-trapping vector, that in the presence of the A allele, only one transcript was observed in RAW264.7 cells, as opposed to two transcripts transcribed in the presence of the G allele. These observations suggest that the linked synonymous variant found in exon 9 of the CD44 gene might be increasing susceptibility to osteoporosis in this family by affecting the splicing mechanism.© 2009 Elsevier Inc. All rights reserved.
IntroductionFor the past 15 years, numerous studies have been performed in different populations using both linkage and association approaches, to try to identify genes that might increase the individual's susceptibility to osteoporosis [1,2]. Most of these studies did not give any conclusive results, and lacked replication due to reasons such as genetic heterogeneity between different populations and low sample power. Still such studies were useful in understanding better the complex pathophysiology of osteoporosis by identifying genes playing a role in various metabolic pathways and other mechanisms that might lead to disease. Linkage studies of monogenic bone diseases revealed several chromosomal regions putting into light various genes that were never thought to be involved in bone physiology such as the low density lipoprotein receptor-related protein (LRP)-5 and sclerostin (SOST) genes [3,4].In a previous linkage study, performed on two Maltese families with a high incidence of osteoporosis, suggestive linkage to chromosome 11p12 was observed [5]. Fine-mapping reduced the linkage interval to a region between markers D11S1392 (50.64 cM) and D11S935 (52.94 cM), with highest total heterogeneity LOD and NPL (3.07 and 7.0, respectively) to marker D11S935. Although both families shared the same linkage interval, highest LOD scores were obtained to two different markers with a spacing of approximately 4 cM between them, showing also different inherited alleles, thus suggesting that different genes might be responsible for the disease in different families [5]. Highest LOD and NPL scores (1.77 and 5.9, respectively) were obtained for marker D11S1392 (50.64 cM) in Pedigree 2, while for Pedigree 1 highest scores were obtained to marker D11S4...
