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A recombinant plasmid containing sequences complementary to human pro-al(I) collagen mRNA was used for the chromosomal assignment of the pro-al(I) collagen gene. Restriction endonuclease analysis of DNA from mouse-human and Chinese hamster-human somatic cell hybrids revealed cosegregation with human chromosome 17. Hybrids containing derivative chromosomes with a t(2;17Xql4;q2l) translocation showed cosegregation ofthe pro-al(I) gene with the segment 17q21+qter. In situ hybridization on human metaphasic chromosomes confirmed this conclusion.At least five genetically distinct collagen types have been identified in mammals. Of these, type I collagen is the most abundant; it is the major constituent of bone, tendon, skin, and fibroblasts. It consists of two al(I) chains and one a2(I) chain, which are synthesized as precursor polypeptides containing NH2-and COOH-terminal propeptides and called pro-al(I) and pro-a2(I) chains (1,2).The availability of genomic libraries has permitted the isolation of the entire chicken pro-a2(I) gene (3-7) and part of the sheep pro-a2(I) (8) and of the mouse pro-al(I) genes (9). More recently, we have reported the isolation of specific cDNAs and genomic fragments for the human pro-a2(I) and pro-al(I) chains (10-13). However, one major question remains: Are the genes coding for the nine (or more) different polypeptide collagen chains dispersed in the genome or clustered as one or several gene family(ies)? Conflicting results have been obtained when immunological techniques were used to determine the chromosomal location ofthe pro-al(I) and pro-a2(I) genes (4, 5). We have used the more direct approach ofrestriction endonuclease analysis of DNA from human-rodent somatic cell hybrids hybridized to labeled cloned cDNAs. Using this method, we have unequivocally assigned the gene coding for pro-a2(I) collagen chain (COLIA2) to human chromosome 7 (14). In the present paper we report the assignment of the gene coding for the proal(I) chain (COLIAl) hybrids, or the parental cells were fused with polyethylene glycol (16) and hybrid cells were selected in ouabain/hypoxanthine/aminopterin/thymidine medium (17) for the other hybrids. For counter-selection, hybrid cells L-53 were grown in standard medium supplemented with 5-bromodeoxyuridine (18). Cell lines were established and maintained as described (18)(19)(20). Cell hybrids were characterized by isozyme and karyotype analysis. Chromosomes were identified by R-banding (21).Recombinant Clones and DNA Analysis. From a human fibroblast cDNA library five overlapping clones specific for the pro-al(I) chain were isolated (12). The clones were characterized by restriction endonuclease mapping and direct DNA sequence analysis was performed according to Maxam and Gilbert (22). Here we have used one of these clones (Hf-677). Nuclear DNA purification and restriction endonuclease analysis were performed as described (14).In Situ Hybridization on Metaphase Chromosomes. A phytohemagglutinin-stimulated culture ofwhole blood from a normal woman was ...

Nance-Horan syndrome (NHS) is an X-linked disease characterized by severe congenital cataract with microcornea, distinctive dental findings, evocative facial features and mental impairment in some cases. Previous linkage studies have placed the NHS gene in a large region from DXS143 (Xp22.31) to DXS451 (Xp22.13). To refine this localization further, we have performed linkage analysis in four families. As the maximum expected Lod score is reached in each family for several markers in the Xp22.31-p22.13 region and linkage to the rest of the X chromosome can be excluded, our study shows that NHS is a genetically homogeneous condition. An overall maximum two-point Lod score of 9.36 (theta = 0.00) is obtained with two closely linked markers taken together. DXS207 and DXS1053 in Xp22.2. Recombinant haplotypes indicate that the NHS gene lies between DXS85 and DXS1226. Multipoint analysis yield a maximum Lod score of 9.45 with the support interval spanning a 15-cM region that includes DXS16 and DXS1229/365. The deletion map of the Xp22.3-Xp21.3 region suggests that the phenotypic variability of NHS is not related to gross rearrangement of sequences of varying size but rather to allelic mutations in a single gene, presumably located proximal to DXS16 and distal to DXS1226. Comparison with the map position of the mouse Xcat mutation supports the location of the NHS gene between the GRPR and PDHA1 genes in Xp22.2.

The CAG expansion responsible for Huntington's disease (HD) is followed by an adjacent polymorphic CCG repeat region which may interfere with a PCR based diagnosis. We have sequenced this region in 52 unrelated HD patients, from both normal and HD chromosomes. Fifty percent of the normal alleles were (CCG)7(CCT)2, 48% (CCG)IO(CCT)2, and 2% (CCG)7(CCT)3. In contrast (CCG)7(CCT)2 was found in 85% ofthe HD alleles which represents significant linkage disequilibrium with the HD mutation.