Molecular Vision 2006; 12:1506-10
An autosomal dominant progressive congenital zonular nuclear cataract linked to chromosome 20p12.2-p11.23
Ningdong Li,1 Yongjia Yang,1,2 Juan Bu,1 Chen Zhao,1 Shasha Lu,1 Jun Zhao,1 Li Yan,1 Lihong Cui,1 Rongchang Zheng,1 Jianjun Li,3 Jinsheng Tang,4 Kanxing Zhao1
(The first two authors contributed equally to this publication)
1Tianjin Eye Hospital, Tianjin Medical University, Tianjin; 2School of Biosciences and Technologies of Central South University, Changsha; 3The People Hospital of Lintao county, Gansu province; 4The Second Affiliated Hospital, Central South University, Changsha, People’s Republic of China
Purpose: To map and to identify the causal gene for autosomal dominant congenital cataract (ADCC) in a Chinese family. Methods: A four-generation family with a history of progressive congenital cataracts was investigated. Twenty-three members of the family were examined ophthalmologically. Blood samples were collected from twenty-nine family mem- bers for genetic linkage analysis. Two-point LOD scores were calculated. Multi-point linkage analysis and haplotype construction were performed to define the optimal cosegregating interval. Direct sequence analysis of the candidate gene, beaded filament structural protein 1, filensin (BFSP1) in the critical region was carried out. Results: Fifteen family members were affected with autosomal dominant progressive congenital zonular nuclear cataract (ADPCZNC). The maximum two-point LOD Score of 6.02 was obtained for marker D20S904 (θ=0). The cataract locus in this family was mapped to chromosome 20p12.2-p11.23, a 9.34 Mb (16.37 cM) interval between markers D20S186 and D20S912. Although BFSP1 was in this critical region, we found no evidence that the condition in the family was caused by a BFSP1 mutation. Conclusions: We have mapped the genetic locus of ADPCZNC to chromosome 20p12.2-p11.23 in an ADCC family. This is the first time ADPCZNC was linked to this region.
Congenital cataract is one of the major causes of blind- METHODS ness in human beings. Although the visual acuity of the pa- A large four-generation family with ADCC from Gansu prov- tients can be improved dramatically by surgical intervention, ince of China was investigated (Figure 1). All adult-individu- the congenital cataract patients are usually accompanied with als and the parents of the minors in this family gave informed intractable complications after operation. In some cases, con- consent to the study protocol, which was approved by the Eth- genital cataracts are hereditary. To date, various inheritance ics committee of Tianjin Eye Hospital (Tianjin, China). patterns for congenital cataract have been reported [1], includ- Twenty-three members of the family were invited for a de- ing autosomal dominant, autosomal recessive, and X-linked tailed clinical examination including direct-flashlight test, dis- [2]. Among these types, autosomal dominant inheritance ap- tance visual acuity, examination with slit-lamp microscope and pears the most common [3]. Currently, a number of loci on examination of the fundus. Detailed medical and family his- different chromosomes associated with ADCC have been docu- tories were obtained from each available family member. mented [1], suggesting that ADCC is a highly heterogeneous Blood samples were collected from 29 family members. condition. In non-consanguineous families, clinically identi- Genomic DNA of all 29 members was isolated by standard cal cataracts have been mapped to inconsistent loci [4]. Con- procedures. All specimens were quantified by spectrophotom- versely, an identical defective gene or a same mutation has etry and diluted to 30 ng/µl for polymerase chain reaction resulted in different phenotypes [5-7]. In this report, we stud- (PCR) amplification. Genome-wide screening was performed ied a Chinese family with autosomal dominant progressive with 382 markers spaced an average of 10 cM apart (ABI congenital zonular nuclear cataract (ADPCZNC) and we have PRISM Linkage Mapping Set, Version 2.5, Applied Bio-sys- presented evidence of linkage to chromosome 20p. Haplotype tems, Foster City, CA). Fine mapping was accomplished us- construction and multiple linkage analysis assigned the cata- ing fluorescently labeled primers from the Decode linkage map ract locus to a 9.34 Mb (16.37 cM) interval between the mark- [8]. Multiplex PCR was carried out in a 5 µl reaction mixture ers D20S186 and D20S912. containing 50 ng of genomic DNA, 1X PCR buffer, 100 µM
of each dNTP, 3.0 mM MgCl2, 60 pmol each of forward and Correspondence to: Kanxing Zhao, Tianjin Eye Hospital, Tianjin reverse primers, and 0.2 U of Ampli Taq Gold DNA poly- Medical University, Tianjin, 300040, People’s Republic of China; merase. The mixture including reaction products (1 µl), Liz Phone: +86-22-23542766; FAX: +86-22-23542524; email: Size Standard-500 (0.2 µl), and Hi-Di Formanmide (9 µl) were [email protected] electrophoresed and visualized on a 3130 Genetic Analyzer 1506 Molecular Vision 2006; 12:1506-10
(Applied Biosystems). Alleles were analyzed by Genescan RESULTS analysis software V3.7 and Genotyper V3.7 (Applied Clinical Findings: A four-generation Chinese family from Biosystems). Ganshu province was identified (Figure 1). After informed The MLINK program of the LINKAGE package (ver- consent, 23 individuals with a family history of cataract and sion 5.1) was used for calculating two-point LOD scores. The six spouses were included in this study. Fifteen of these 23 disease was assumed to be an autosomal dominant trait with family members were affected with ADPCZNC. None of the 99% penetrance. Equal male and female recombination rates spouses showed signs of the disease. Some parents of the af- were assumed. Marker allele frequencies were set at 1/n (where fected individuals recalled that the cataracts presented at birth n is the number of alleles observed). We assumed gene fre- and a progressive visual loss appeared during the first decade quencies of 0.0001. Multi-point linkage analysis was used to of life (most of them were 2-6 years old). There was no his- estimate the optimal position. For multi-point linkage calcu- tory of other ocular or systemic abnormalities in the family. lation, the genetic distances between loci were obtained from Autosomal dominant inheritance was supported by the results the Decode linkage map [8]. The haplotype was constructed of pedigree analysis, which presented affected individuals in using the Cyrillic program to define the borders of the each of four generations, about equal number of affected males cosegregating region. Direct cycle sequencing of beaded fila- and females and male to male transmission. Penetrance in this ment structural protein 1, filensin (BFSP1) was carried out on family appeared complete. three family members (two affected and one unaffected).
Figure 1. Haplotype analysis of the ADPZNC family. Haplotype analysis of the ADPZNC family. Markers are listed from top to bottom: telomere- D20S186- D20S163- D20S915- D20S152- D20S98- D20S904- D20S875- D20S112- D20S1140- D20S432- D20S912- D20S54- D20S477- D20S101- centromere. The haplotype co-segregating with the ADPCZNC phenotype is dark-boxed. A question mark indicates that the genotype is not determined. 1507 Molecular Vision 2006; 12:1506-10
In this family, 15 affected members had bilateral zonular nuclear cataracts (typical features shown in Figure 2). The opacification was symmetrical, homogeneous, and of the same
TABLE 1. TWO-POINT LOD SCORE WITH POLYMORPHIC DNA MARKERS ON CHROMOSOME 20P
Figure 2. Multipoint linkage analysis. Multipoint LOD scores. The markers and intervals: D20S186-2.11 cM- D20S163-0.93 cM- D20S915-1.59 cM- D20S152-2.36 cM- D20S904-1.89 cM- D20S875-0.89 cM- D20S112-1.41 cM- D20S1140-2.78 cM- D20S432-0.41 cM- D20S912-0.43 cM- D20S54-0.52 cM-D20S477- 1.74 cM- D20S101. Multipoint LOD scores with the support inter- val narrow the ADPCZNC locus to a 16.37 cM region between mark- ers D20S186 and D20S912.
Figure 3. Slit lamp photography. Slit lamp photography of a family member (III:15, 31 years old). A: Slit view of the lens and cornea. B: Figure 4. ADCC loci on chromosome 20. A shows the CPP3 locus Front view of the lens. [9] and B shows the ADPCZNC locus presented in this report. 1508 Molecular Vision 2006; 12:1506-10
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The print version of this article was created on 5 Dec 2006. This reflects all typographical corrections and errata to the article through that date. Details of any changes may be found in the online version of the article. α 1510