Identification and analysis of a novel gene causing the pleiotropic features of Nance–Horan Syndrome.

Abstract

Abstract: : Purpose: Nance–Horan syndrome (NHS) is an X–linked disorder characterized by congenital cataracts, dental anomalies, dysmorphic facial features and mental retardation in some males. The NHS gene was previously mapped to chromosome Xp22.13. The purpose of this study was to perform positional cloning of the NHS gene, conduct detailed expression studies, and evaluate the mutation spectrum in NHS families and families with isolated X–linked cataract. Methods: A novel candidate gene predicted by GeneScan software and supported by relevant tissue ESTs was evaluated. Genomic structure was determined using RT–PCR and 5' RACE. Bidirectional direct sequencing was used to screen for mutations. Expression studies were performed by RT–PCR, Northern blot analysis, in situ hybridisation, and analysis of a mouse LacZ line with an intronic insertional mutation. Results:Evaluation of the gene structure revealed 9 exons spanning 650 kb with 2 isoforms. Protein truncating mutations have been identified in 6 NHS families including the original Australian pedigree, and one sporadic case. In one NHS family, no coding or regulatory mutations were identified, and as yet no mutations have been found in 5 families with isolated X–linked cataract. Expression of the NHS gene has been demonstrated at low levels in all tissues tested, but there is developmentally and spatially regulated expression in tissues involved in NHS such as the developing lens, tooth primordia and the brain. Expression was also found in the developing retina, notochord, olfactory epithelium, and the limbic system. There are nuclear localization signals, but no other significant sequence similarity to any known gene has been identified. Conclusions: Mutations in this novel gene cause the pleiotropic features of NHS, and it is likely to have as yet unknown key functions in the regulation of eye, tooth, craniofacial and brain development. There appears to be genetic heterogeneity in X–linked cataract.

Keywords: gene mapping • gene/expression • cataract