A New Locus for Autosomal Dominant Congenital Cataracts Maps to Chromosome 3 Patricia L. Kramer,1,2 Dante LaMorticella,2 Karla Schilling,1 Andrea M. Billingslea,3 Richard G. Weleber,2,3 and Michael Litt2 PURPOSE. To map a gene for cataracts in a family with congenital nuclear and sutural cataracts and to examine candidate genes in the linked region. METHODS. A large family with autosomal dominant congenital nuclear and sutural cataracts was identified and characterized. A genome-wide screen was conducted with a set of markers spaced at 10- to 15-cM intervals, and linkage was assessed using standard LOD score analysis. RESULTS. Fifteen (15) affected individuals were identified. This form of congenital cataracts maps to a 12-cM region on chromosome 3q21.2-q22.3 between markers D3S3674 and D3S3612, with a maximum multipoint LOD score of 6.94 at D3S1273. The crystallin gene, CRYGS, was excluded as a candidate gene for this locus. CONCLUSIONS. There are now more than 12 different genetic loci that cause congenital cataracts. The most recent locus to be identified is on chromosome 3q21.2-q22.3, in a family with congenital nuclear and sutural cataracts. (Invest Ophthalmol Vis Sci. 2000;41:36–39) ataracts refer to the loss of transparency in the crystal- informed consent to the study protocol, which was approved lin lens of the eye. The opaque appearance behind the by the institutional review board of Oregon Health Sciences Cpupil is due to changes in proteins within the lens University and which conforms to the tenets of the Declaration fibers. Congenital cataracts are among the most prevalent ma- of Helsinki. DNA was available for 31 family members (12 jor eye diseases and frequently cause blindness in infants.1 affected, 13 unaffected, and 6 spouses). They can occur as a primary disorder, or secondarily in asso- Affected family members had congenital nuclear and sutural ciation with multisystem disorders, such as Down’s syndrome, cataracts that varied in severity among different individuals. Many galactosemia, Wilson’s disease, and myotonic dystrophy. had had bilateral cataract surgery during early childhood, often at Approximately half of all cases of congenital cataracts are ages 3 to 5 years, but occasionally in the late teens. Several family familial, and autosomal dominant congenital cataracts (ADCC) members never had surgery, even in the presence of moderate appear to be the most common form.1 At least 15 loci have sutural and nuclear opacities. One 20-year-old woman with visual been reported for various primary forms of ADCC. Hejtmancik2 acuities of 20/40 OD and 20/30 OS had striking anterior and reviewed nine, and the others were reported more recently.3–5 posterior sutural opacities with some smaller scattered whitish Although some of these forms exhibit distinct phenotypes, cortical opacities and radially oriented fine vacuoles. there is substantial phenotypic overlap.2 We have been studying a family with ADCC, and we present DNA Analysis evidence for linkage to chromosome 3q. Three loci in the region Typing with microsatellite markers was performed as previ- are discussed as potential candidate loci for this ADCC locus. ously described.6 We conducted a full genome scan using a panel of markers spaced at approximately 10-cM intervals (We- ber Screening Set 8; Research Genetics, Huntsville, AL; http:// METHODS www.resgen.com/). Family and Clinical Data Primers for amplification of a 144-bp segment of CRYGS were designed from the partial cDNA sequence of human CRYGS The family comprised 15 affected and more than 15 unaffected (GenBank accession number L36869; available at http://ncbi.nlm. individuals across three generations (Fig. 1). Participants gave nih.gov/). Primer sequences were CRYGS/f: TGTGCAGATTTC- CACACATACC and CRYGS/r: CATCCAACGCTGGTATTCAG. From the Departments of 1Neurology, 2Molecular and Medical Linkage Analysis Genetics, and 3Ophthalmology, Oregon Health Sciences University, Linkage analysis was conducted using the computer program Portland. VITESSE.7 We assumed autosomal dominant inheritance of a Supported by Grant R01-EY11710 from the National Institutes of Health (ML). The work of RGW was supported in part by an unre- rare gene (frequency 0.0001), with nearly complete pen- stricted grant from Research to Prevent Blindness. etrance (0.95). Because symptoms occur early in childhood, Submitted for publication May 21, 1999; revised August 3, 1999; no age correction for penetrance was required. Marker allele accepted August 27, 1999. frequencies were assumed to be equal. Map locations and Commercial relationships policy: N. Corresponding author: Patricia L. Kramer, Department of Neurol- distances were based on data obtained at the Genetic Loca- ogy, CR131, Oregon Health Sciences University, Portland, Oregon tion Database [Southampton, UK (http://cedar.genetics.soton. 97201. [email protected] ac.uk/)]. Investigative Ophthalmology & Visual Science, January 2000, Vol. 41, No. 1 36 Copyright © Association for Research in Vision and Ophthalmology Downloaded from tvst.arvojournals.org on 09/26/2021 IOVS, January 2000, Vol. 41, No. 1 Congenital Cataracts Locus on Chromosome 3 37 FIGURE 1. Pedigree of the ADCC family and haplotypes with chromosome 3 markers from D3S3674 to D3S3612 (the order of the markers is indicated in the box in the upper left corner). (f/F) Affected individuals; (M/E) unaffected individuals; (?) unknown phenotype. The haplotype segregating with the disease is boxed. Critical crossovers in individuals II-6 (D3S1309–D3S3612) and IV-3 (D3S3674–D3S1292) define the region containing the new ADCC locus on chromosome 3q. FIGURE 2. Results of the chromo- some 3 multipoint linkage analysis. The maximum multipoint LOD score (6.94) occurs at D3S1273. Markers and intermarker distances are indicated on the horizontal axis. Downloaded from tvst.arvojournals.org on 09/26/2021 38 Kramer et al. IOVS, January 2000, Vol. 41, No. 1 TABLE 1. Two-Point LOD Scores for Chromosome 3 Markers in an ADCC Family LOD score at Q Map Marker Location Order 0.00 0.01 0.05 0.10 0.20 0.30 139.6 D3S3674 20.19 4.27 4.57 4.34 3.50 2.40 143.4 D3S1292 4.34 4.26 3.97 3.58 2.73 1.79 143.8 D3S1273 6.65 6.54 6.09 5.50 4.23 2.82 149.2 D3S1549 6.37 6.27 5.85 5.30 4.11 2.76 151.9 D3S1309 3.90 3.91 3.84 3.62 2.94 2.05 152.2 D3S3612 23.48 20.74 0.03 0.30 0.40 0.25 RESULTS After excluding large regions of the genome, we obtained positive LOD scores for markers on chromosome 3q21.2-q22.3 that span approximately 12 cM. The maximum two-point LOD was obtained at D3S1273 (6.65 at w 5 0). The markers, their map location, and two-point LOD scores are shown in Table 1 Haplotype data are given in Figure 1. A crossover between D3S3674 and D3S1292 in individual IV-3 defines the proximal border of the region, and one between D3S1309 and D3S3612 in individual II-6 defines the distal border. Results of multipoint analysis are presented in Figure 2. The maximum multipoint LOD score (6.94) occurs across the 0.4-cM region from D3S1292 to D3S1273, and the 1-LOD-unit confidence interval extends from D3S3674 to D3S3612. This region corresponds to 3q21.3-q22.2 on the cytogenetic map (Genetic Location data- base), illustrated in Figure 3. All affected individuals have an affected parent, and there are no unaffected individuals who carry the disease haplotype. Thus, penetrance appears to be virtually complete in this family. Crystallin genes are obvious candidate genes for cataracts, because they function as major structural proteins in the lens. Mutations in crystallin genes have been shown to cause ADCC in human families and in several rodent groups.2,5,8–10 Because the g-crystallin gene CRYGS maps to chromosome 3,11 we considered it a candidate gene for the chromosome 3 ADCC locus. Because regional localization of CRYGS has not been reported, we used radiation hybrid mapping to localize this FIGURE 3. Ideogram of chromosome 3. The markers that define this gene on the chromosome. Mapping was accomplished by ADCC locus span the region 3q21.2-q22.3 screening the Genebridge 4 radiation hybrid panel (Research Genetics) with primers CRYGS/f and CRYGS/r. The results are TABLE 2. Genebridge 4 Panel Radiation Hybrid Mapping Data shown in Table 2. CRYGS maps in proximity, but probably for CRYGS distal to WI9695, the most telomeric marker on the framework radiation hybrid map of chromosome 3q. Because this location Marker Data Vector* Distance† LOD Score‡ is more than 60 cM distal to the cataract gene in our family, we WI9695 00000000100000001000000 26.0 F excluded it as a candidate gene for this ADCC locus. 01001110100110010001000 00001120200001011010001 000011010000002000010200 DISCUSSION CRYGS 00000000010010001021102 0.0 P1.49 01011102100110011021000 Hess et al.12 localized a gene, LIFL-L, for the protein CP47 to 00001010100001212000000 010011000000101000010100 chromosome 3q21-q25. CP47 is a component of the beaded filament, a cytoskeletal structure that is abundant in lens fiber *The data vector shows data arranged in the order specified for the cells and is an excellent candidate gene for ADCC. We are Whitehead/MIT on-line Radiation Hybrid Mapper Program (http://car- currently mapping this gene on a radiation hybrid panel to bon.wi.mit.edu:8000/cgi-bin/contig/rhmapper/pl/). 0, negative; 1, localize it more precisely; if it localizes to the critical region for positive; 2, uncertain data. †Distance in centiRads from the marker immediately above in the ADCC reported here, we will scan it for mutations. 13 table. Recently, Ranum et al. mapped a second myotonic dystro- ‡The placement marker is indicated by a P followed by the LOD phy locus (DM2) to an 8-cM region from D3S3674 distal to score relative to the next most likely placement.