Two novel WTX mutations underscore the unpredictability of male survival in osteopathia striata with cranial sclerosis.

Osteopathia striata with cranial sclerosis (OMIM ##300373) is an X-linked dominant sclerosing bone dysplasia that presents in females with macrocephaly, cleft palate, mild learning disabilities, sclerosis of the long bones and skull, and longitudinal striations visible on radiographs of the long bones, pelvis, and scapulae. In males this entity is usually associated with foetal or neonatal lethality, because of severe heart defects and/or gastrointestinal malformations, and is often accompanied by bilateral fibula aplasia. Recently, the disease-causing gene was identified as the WTX gene (FAM123B). Initially it was suggested that the mutations in the 5' region of the WTX gene are associated with male lethality. Mutation analysis in individuals of two families diagnosed with OSCS revealed two novel WTX mutations. In one family, the affected male is still alive in his teens. These mutations underline the unpredictability of male survival and suggest that WTX mutations should be considered in cases of male cranial sclerosis, even if striations are not present. An overview of all known mutations and their associated characteristics provide a valuable resource for the molecular analysis of OSCS.

Refined genomic localization of the genetic lesion in the osteopetrosis (op) rat and exclusion of three positional and functional candidate genes, Clcn7, Atp6v0c, and Slc9a3r2.

Osteopetrosis is a disease characterised by a generalized skeletal sclerosis resulting from a reduced osteoclast-mediated bone resorption. Several spontaneous mutations lead to osteopetrotic phenotypes in animals. Moutier et al. (1974) discovered the osteopetrosis (op) rat as a spontaneous, lethal, autosomal recessive mutant. op rats have large nonfunctioning osteoclasts and severe osteopetrosis. Dobbins et al. (2002) localized the disease-causing gene to a 1.5-cM genetic interval on rat chromosome 10, which we confirm in the present report. We also refined the genomic localization of the disease gene and provide statistical evidence for a disease-causing gene in a small region of rat chromosome 10. Three strong functional candidate genes are within the delineated region. Clcn7 was previously shown to underlie different forms of osteopetrosis, in both human and mice. ATP6v0c encodes a subunit of the vacuolar H(+)-ATPase or proton pump. Mutations in TCIRG1, another subunit of the proton pump, are known to cause a severe form of osteopetrosis. Given the critical role of proton pumping in bone resorption, the Slc9a3r2 gene, a sodium/hydrogen exchanger, was also considered as a candidate for the op mutation. RT-PCR showed that all 3 genes are expressed in osteoclasts, but sequencing found no mutations either in the coding regions or in intron splice junctions. Our ongoing mutation analysis of other genes in the candidate region will lead to the discovery of a novel osteopetrosis gene and further insights into osteoclast functioning.