A Common Ancestral Mutation in CRYBB3 Identified in Multiple Consanguineous Families with Congenital Cataracts.
OBJECTIVE
This study was performed to investigate the genetic determinants of autosomal recessive congenital cataracts in large consanguineous families.


METHODS
Affected individuals underwent a detailed ophthalmological examination and slit-lamp photographs of the cataractous lenses were obtained. An aliquot of blood was collected from all participating family members and genomic DNA was extracted from white blood cells. Initially, a genome-wide scan was performed with genomic DNAs of family PKCC025 followed by exclusion analysis of our familial cohort of congenital cataracts. Protein-coding exons of CRYBB1, CRYBB2, CRYBB3, and CRYBA4 were sequenced bidirectionally. A haplotype was constructed with SNPs flanking the causal mutation for affected individuals in all four families, while the probability that the four familial cases have a common founder was estimated using EM and CHM-based algorithms. The expression of Crybb3 in the developing murine lens was investigated using TaqMan assays.


RESULTS
The clinical and ophthalmological examinations suggested that all affected individuals had nuclear cataracts. Genome-wide linkage analysis localized the causal phenotype in family PKCC025 to chromosome 22q with statistically significant two-point logarithm of odds (LOD) scores. Subsequently, we localized three additional families, PKCC063, PKCC131, and PKCC168 to chromosome 22q. Bidirectional Sanger sequencing identified a missense variation: c.493G>C (p.Gly165Arg) in CRYBB3 that segregated with the disease phenotype in all four familial cases. This variation was not found in ethnically matched control chromosomes, the NHLBI exome variant server, or the 1000 Genomes or dbSNP databases. Interestingly, all four families harbor a unique disease haplotype that strongly suggests a common founder of the causal mutation (p<1.64E-10). We observed expression of Crybb3 in the mouse lens as early as embryonic day 15 (E15), and expression remained relatively steady throughout development.


CONCLUSIONS
Here, we report a common ancestral mutation in CRYBB3 associated with autosomal recessive congenital cataracts identified in four familial cases of Pakistani origin.
Ophthalmic Genetics and Visual Function Branch, National Eye Institute, National Institutes of Health, Bethesda, MD, 20892, United States of America.
Xiaodong
X
Jiao
The Wilmer Eye Institute, Johns Hopkins University School of Medicine, Baltimore, MD, 21287, United States of America.
Firoz
F
Kabir
The Wilmer Eye Institute, Johns Hopkins University School of Medicine, Baltimore, MD, 21287, United States of America.|National Centre of Excellence in Molecular Biology, University of the Punjab, Lahore, 53700, Pakistan.
Bushra
B
Irum
King Khaled Eye Specialist Hospital, Riyadh, 12329, Saudi Arabia.
Arif O
AO
Khan
Ophthalmic Genetics and Visual Function Branch, National Eye Institute, National Institutes of Health, Bethesda, MD, 20892, United States of America.
Qiwei
Q
Wang
Ophthalmic Genetics and Visual Function Branch, National Eye Institute, National Institutes of Health, Bethesda, MD, 20892, United States of America.
David
D
Li
National Centre of Excellence in Molecular Biology, University of the Punjab, Lahore, 53700, Pakistan.
Asma A
AA
Khan
National Centre of Excellence in Molecular Biology, University of the Punjab, Lahore, 53700, Pakistan.
Tayyab
T
Husnain
Allama Iqbal Medical College, University of Health Sciences, Lahore, 54550, Pakistan.|National Centre for Genetic Diseases, Shaheed Zulfiqar Ali Bhutto Medical University, Islamabad, Pakistan.
Javed
J
Akram
National Centre of Excellence in Molecular Biology, University of the Punjab, Lahore, 53700, Pakistan.|Allama Iqbal Medical College, University of Health Sciences, Lahore, 54550, Pakistan.|National Centre for Genetic Diseases, Shaheed Zulfiqar Ali Bhutto Medical University, Islamabad, Pakistan.
Sheikh
S
Riazuddin
Ophthalmic Genetics and Visual Function Branch, National Eye Institute, National Institutes of Health, Bethesda, MD, 20892, United States of America.
J Fielding
JF
Hejtmancik
The Wilmer Eye Institute, Johns Hopkins University School of Medicine, Baltimore, MD, 21287, United States of America.
S Amer
SA
Riazuddin
D000818:Animals; D001483:Base Sequence; D002386:Cataract / Q000151:congenital* / Q000235:genetics*; D002892:Chromosomes, Human, Pair 22 / Q000235:genetics; D003241:Consanguinity; D005190:Family; D005260:Female; D020869:Gene Expression Profiling; D005819:Genetic Markers; D006239:Haplotypes / Q000235:genetics; D006801:Humans; D007908:Lens, Crystalline / Q000196:embryology / Q000378:metabolism; D008126:Lod Score; D008297:Male; D051379:Mice; D018895:Microsatellite Repeats / Q000235:genetics; D009154:Mutation / Q000235:genetics*; D010375:Pedigree; D020641:Polymorphism, Single Nucleotide / Q000235:genetics; D066167:Slit Lamp; D038206:beta-Crystallin B Chain / Q000235:genetics*
C103908:CRYBB3 protein, human; D005819:Genetic Markers; D038206:beta-Crystallin B Chain