Gene encoding a new RING-B-box-Coiled-coil protein is mutated in mulibrey nanism.

Mulibrey nanism (for muscle-liver-brain-eye nanism, MUL; MIM 253250) is an autosomal recessive disorder that involves several tissues of mesodermal origin, implying a defect in a highly pleiotropic gene. Characteristic features include severe growth failure of prenatal onset and constrictive pericardium with consequent hepatomegaly. In addition, muscle hypotonia, J-shaped sella turcica, yellowish dots in the ocular fundi, typical dysmorphic features and hypoplasia of various endocrine glands causing hormonal deficiency are common. About 4% of MUL patients develop Wilms' tumour. MUL is enriched in the Finnish population, but is rare elsewhere. We previously assigned MUL to chromosome 17q22-q23 and constructed a physical contig over the critical MUL region. The region has now been further refined by haplotype analysis and new positional candidate genes have been localized. We identified a gene with four independent MUL-associated mutations that all cause a frameshift and predict a truncated protein. MUL is ubiquitously expressed and encodes a new member of the RING-B-box-Coiled-coil (RBCC) family of zinc-finger proteins, whose members are involved in diverse cellular functions such as developmental patterning and oncogenesis.

High-resolution physical and genetic mapping of the critical region for Meckel syndrome and Mulibrey Nanism on chromosome 17q22-q23.

Previously, we assigned the genes for two autosomal recessive disorders, Meckel syndrome (MKS; MIM 249000) and Mulibrey Nanism [MUL (muscle-liver-brain-eye Nanism); MIM 253250] that are enriched in the Finnish population, to overlapping genomic regions on chromosome 17q. Now, we report the construction of a bacterial clone contig over the critical region for both disorders. Several novel CA-repeat markers were isolated from these clones, which allowed refined mapping of the MKS and MUL loci using haplotype and linkage disequilibrium analysis. The localization of the MKS locus was narrowed to <1 cM between markers D17S1290 and 132-CA, within an approximately 800-kb region. The MUL locus was refined into an approximately 1400-kb interval between markers D17S1290 and 52-CA. The whole MKS region falls within the MUL region. In the common critical region, the conserved haplotypes were different in MKS and MUL patients. A trancript map was constructed by assigning expressed sequence tags (ESTs) and genes, derived from the human gene map, to the bacterial clone contig. Altogether, four genes and a total of 20 ESTs were precisely localized. These data provide the molecular tools for the final identification of the MKS and the MUL genes.