Report of a critical recombination further narrowing the TSC1 region

Chromosomal localization, gene structure and transcription pattern of the ORFX gene, a homologue of the MHC-linked RING3 gene

We have mapped the human ORFX gene to chromosome 9q34 and determined its complete gene structure. Comparison with RING3, the human MHC-linked homologue on 6p21.3, shows the two gene structures to be highly conserved but with an approximate threefold expansion in the ORFX introns. RING3 and ORFX are found to be ubiquitously expressed in human adult and foetal tissues. Evidence suggests that the two genes may have arisen from an ancient duplication in a common ancestral chromosome.

Human XPMC2H: cDNA cloning, mapping to 9q34, genomic structure, and evaluation as TSC1

XPMC2 is a Xenopus gene identified on the basis of its ability to correct a mitotic defect in fission yeast. Here we report the identification of cDNA clones for human XPMC2H, its mapping to the tuberous sclerosis gene TSC1 region on 9q34, determination of genomic structure, and identification of several coding region polymorphisms. The predicted protein has strong sequence similarity to the Xenopus gene. Through SSCP and heteroduplex analysis of genomic DNA, we found two intragenic polymorphisms but no evidence for significant mutations in patients with tuberous sclerosis in this gene.

Identification of the tuberous sclerosis gene TSC1 on chromosome 9q34

Tuberous sclerosis complex (TSC) is an autosomal dominant disorder characterized by the widespread development of distinctive tumors termed hamartomas. TSC-determining loci have been mapped to chromosomes 9q34 (TSC1) and 16p13 (TSC2). The TSC1 gene was identified from a 900-kilobase region containing at least 30 genes. The 8.6-kilobase TSC1 transcript is widely expressed and encodes a protein of 130 kilodaltons (hamartin) that has homology to a putative yeast protein of unknown function. Thirty-two distinct mutations were identified in TSC1, 30 of which were truncating, and a single mutation (2105delAAAG) was seen in six apparently unrelated patients. In one of these six, a somatic mutation in the wild-type allele was found in a TSC-associated renal carcinoma, which suggests that hamartin acts as a tumor suppressor.

Molecular analysis of the human vitamin D binding protein (group specific component, Gc) in tuberous sclerosis complex (TSC)

Group specific component (Gc) is an abundant plasma protein whose functional role is not clearly established. Gc protein is synthesised in the liver and is known to bind vitamin D, vitamin D metabolites, and G actin; Gc protein is also implicated in macrophage activation. Several polymorphic electrophoretic variants of Gc protein are found in all human populations; the most common alleles are Gc-1f, Gc-1s, and Gc-2. In previous studies, Gc allele frequencies, determined using isoelectric focusing or immunofixation or both, were significantly different in patients with tuberous sclerosis complex (TSC) from matched controls, with an excess of Gc-2 in patients. Linkage association between Gc and TSC is unlikely since the Gc locus maps to chromosome 4q12, whereas the two common forms of TSC map to 9q34 and 16p13.1, respectively. However, a direct cause and effect relationship between Gc protein and TSC symptoms is possible. To investigate further the relationship between the Gc locus and TSC, two Gc restriction site polymorphisms, HaeIII and StyI, were typed in 43 unrelated white subjects with TSC. The frequencies of the restriction site polymorphisms in the TSC patients did not differ from those in control populations. Therefore a direct association between Gc type and TSC is unlikely. The previously reported association was either spurious or the result of typing errors in plasma from subjects with underlying abnormalities in plasma proteins.