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Purpose: To map and identify the mutated gene for autosomal dominant cataract (ADC) in family ADC4., Methods: Ophthalmic evaluations were performed on an American family with ADC and a panel of polymorphic DNA sequence-tagged site (STS) markers for known ADC loci and other genome-wide polymorphic markers were used to map the gene; two-point lod scores were calculated. Fine mapping was undertaken in the chromosomal regions of maximum lod scores, and candidate genes were sequenced., Results: A four-generation American family with ADC was studied. The only phakic individual exhibited white and vacuolated opacities in the cortical region. This ADC locus mapped to several suggestive chromosomal regions. Assuming full penetrance, the highest calculated maximum lod score was 3.91 with D19S903 [corrected] On chromosome 12, we sequenced all exons and the exon-intron borders of the membrane intrinsic protein (MIP) gene. On chromosome 19, all exons and the exon-intron borders of genes for lens intrinsic membrane2 (LIM2), ferritin light chain (FTL), and the human homologue of the Drosophila sine oculis homeobox 5 (SIX5) were sequenced, and the 3' untranslated repeat region (UTR) of the dystrophy (DMPK) gene and both the 5' and 3' UTRs of the SIX5 genes were amplified; the promoter for LIM2 was sequenced. For these genes, the sequence matched that in the reference libraries, and the DMPK gene had a normal number of CTG repeats., Conclusions: The mutated gene in ADC4 probably represents a new, not yet identified locus on chromosome 19. In one phakic member, the cortical cataracts were punctate and vacuolated.

Purpose: To further elucidate the cataract phenotype, and identify the gene and mutation for autosomal dominant cataract (ADC) in an American family of European descent (ADC2) by sequencing the major intrinsic protein gene (MIP), a candidate based on linkage to chromosome 12q13., Design: Observational case series and laboratory experimental study., Methods: We examined two at-risk individuals in ADC2. We PCR-amplified and sequenced all four exons and all intron-exon boundaries of the MIP gene from genomic and cloned DNA in affected members to confirm one variant as the putative mutation., Results: We found a novel single deletion of nucleotide (nt) 3223 (within codon 235) in exon four, causing a frameshift that alters 41 of 45 subsequent amino acids and creates a premature stop codon., Conclusions: We identified a novel single base pair deletion in the MIP gene and conclude that it is a pathogenic sequence alteration.

Purpose: To map the locus for autosomal dominant cataracts (ADCs) in a Brazilian family using candidate gene linkage analyses, describe the clinical variability, and identify potential mutations in the human betaA1-crystallin gene (CRYBA1), a candidate gene identified through linkage studies demonstrating cosegregation with markers on chromosome 17., Methods: Members of a Brazilian family with ADC were studied. Clinical examinations and linkage analyses with polymerase chain reaction (PCR) polymorphisms of 22 anonymous markers and 2 within the neurofibromatosis type 1 gene were performed; two-point lod scores were calculated. DNA sequences of all 6 exons and 12 exon-intron boundaries of the betaA1-crystallin gene, a proximal candidate gene mapped to 17q11.1-q12 in one unaffected and two affected individuals, were screened and new variants assessed for cosegregation with the disease., Results: Affected individuals exhibited variable expressivity of pulverulent opacities in the embryonal nucleus and sutures; star-shaped, shieldlike, or radial opacities in the posterior embryonal nucleus; and/or midcortical opacities. All known loci for ADC in this family on chromosomes 1 and 13 were excluded. A positive lod score on chromosome 17 was calculated. This ADC locus was mapped to two potential regions on the long arm with an intervening recombination. The only known candidate gene in these regions was betaA1-crystallin. Three previously unreported single nucleotide variants were found in this gene, one in the donor splice junction site of intron C. This variant was found in all affected members and is presumed to be the causative mutation., Conclusions: An ADC locus was mapped in a Brazilian family with variable expressivity to either 17q23.1-23.2 or 17q11.1-12 based on linkage analyses. Analyses of DNA sequences of the betaA1-crystallin gene in this family revealed three new variants, one of which is within a donor splice junction and cosegregates with affected members.

Purpose: To map the gene for autosomal dominant cataracts (ADC) in an American white family of European descent., Methods: Ophthalmic examinations and linkage analyses using a variety of polymorphisms were performed; two-point lod scores calculated., Results: Affected individuals (14 studied) exhibited variable expressivity of embryonal nuclear opacities based on morphology, location within the lens, and density. This ADC locus to 12q13 was mapped on the basis of statistically significantly positive lod scores and no recombinations (theta(m) = theta(f) = 0) with markers D12S368, D12S270, D12S96, D12S359, D12S1586, D12S312, D12S1632, D12S90, and D12S83; assuming full penetrance, a maximum lod score of 4.73 was calculated between the disease locus and D12S90., Conclusions: The disease in this family represents the first ADC locus on chromosome 12; major intrinsic protein of lens fiber (MIP) is a candidate gene.

Purpose: Gap junctions play a critical role in the metabolic homeostasis and maintenance of transparency of fibers within the ocular lens. As part of a long-term effort to establish the relationship between lens gap junction proteins, normal lens development, and cataractogenesis, we report here the regional localization of the human MP70 (Connexin 50) gene., Methods: Fluorescence in situ hybridization (FISH) was used to regionally map the human MP70 gene. The DNA probe contained the entire MP70 coding region within a clone isolated from a human genomic DNA library., Results: The human gene encoding the lens intrinsic membrane protein MP70 was regionally mapped to q21.1 on the long arm of chromosome 1., Conclusions: This study confirms the previous provisional assignment of MP70 to human chromosome 1 and regionally localizes the gene to 1q21.1. When combined with previous mapping information, these data are consistent with the hypothesis that a genetic lesion in the gene encoding the lens intrinsic membrane protein MP70 may be the underlying molecular defect for zonular pulverulent (Coppock) cataract. Furthermore, these combined data support the hypothesis that other forms of human hereditary cataract may be the result of a mutation in one or more of the genes encoding gap junction proteins found in the ocular lens.

Human chromosome 6 encodes both the interferon gamma receptor as well as the class I major histocompatibility complex antigens, HLA-A, -B, and -C. However, the presence of chromosome 6 in somatic cell hybrids is insufficient to confer sensitivity to human interferon gamma (Hu-IFN-gamma) as assayed by class I HLA induction; it is necessary for both human chromosomes 6 and 21 to reside in the hybrid to generate a response to Hu-IFN-gamma. Treatment of such a hamster-human hybrid, Q72-18, with Hu-IFN-gamma induces the class I HLA antigens. Q72-18 cells selected by fluorescence-activated cell sorting for the loss of class I HLA induction also lost human chromosome 21. Fusions of such cells to a hybrid that contains only human chromosome 21 reconstitutes HLA antigen induction by Hu-IFN-gamma. Furthermore, fusions of hybrids containing a translocated human chromosome 6q and the HLA-B7 gene to a line containing only human chromosome 21 or a translocated 21q also reconstitutes HLA-B7 mRNA and antigen induction by Hu-IFN-gamma. Thus the segregation of cells on the basis of a biological effect by fluorescence-activated cell sorting and reconstitution by hybrid fusion provides a strategy by which some biological pathways can be mapped at a chromosomal level.