Autosomal recessive congenital cataract in consanguineous Pakistani families is associated with mutations in GALK1

Abstract

Purpose: To identify the pathogenic mutations responsible for autosomal recessive congenital cataracts in consanguineous Pakistani families.

Methods: All affected individuals underwent detailed ophthalmologic and medical examination. Blood samples were collected and genomic DNA was extracted. A genome-wide scan was performed with polymorphic microsatellite markers on genomic DNA from affected and unaffected family members and logarithm of odds (LOD) scores were calculated. All coding exons of galactokinase (GALK1) were sequenced to identify pathogenic lesions.

Results: Clinical records and ophthalmological examinations suggested that affected individuals have nuclear cataracts. Linkage analysis localized the critical interval to chromosome 17q with a maximum LOD score of 5.54 at theta=0, with D17S785 in family PKCC030. Sequencing of GALK1, a gene present in the critical interval, identified a single base pair deletion: c.410delG, which results in a frame shift leading to a premature termination of GALK1: p.G137fsX27. Additionally, we identified a missense mutation: c.416T>C, in family PKCC055 that results in substitution of a leucine residue at position 139 with a proline residue: p.L139P, and is predicted to be deleterious to the native GALK1 structure.

Conclusions: Here, we report pathogenic mutations in GALK1 that are responsible for autosomal recessive congenital cataracts in consanguineous Pakistani families.

Figure 1

Pedigree drawing and haplotypes of chromosome 17q markers of family PKCC030. Squares are males, circles are females, and filled symbols are affected individuals; the double line between individuals indicates consanguinity and the diagonal line through a symbol is a deceased family member. The haplotypes of 6 adjacent chromosome 17q microsatellite markers are shown with alleles forming the risk haplotype are shaded black, alleles co-segregating with cataracts but not showing homozygosity are shaded gray and alleles not co-segregating with cataracts are shown in white.

Figure 2

Slit lamp photographs of the affected individual 14 of family PKCC030 show nuclear cataracts that developed in early infancy.

Figure 3

Forward and reverse sequence chromatograms illustrating a single base pair deletion in GALK1. A: Individual 11 homozygous for wild type allele. B: Individual 13 heterozygous for mutant and wild type allele. C: Individual 14 homozygous for the single base pair deletion in exon 3; c.410delG. This deletion leads to a frame shift in the open reading frame of GALK1, which results in a premature termination of the protein: p.G137fsX27.

Figure 4

Pedigree drawing of family PKCC055 and alignment of L139 in GALK1 orthologs. A: Illustration of the chromosome 17q haplotypes and segregation of c.416T>C variation with the disease phenotype. B: Conservation of L139 in other GALK1 orthologs is illustrated with primates colored green; placental mammals blue; and vertebrates are purple. The arrow points to amino acid L139.