Genetic analysis of two Indian families affected with congenital hereditary endothelial dystrophy: two novel mutations in SLC4A11

Abstract

Purpose: The autosomal recessive form of congenital hereditary endothelial dystrophy (CHED2) is a rare eye disorder caused by mutations in the SLC4A11 gene located at the CHED2 locus on chromosome 20p13-p12. The purpose of this study was to carry out genetic analysis of CHED2 in two Indian families.

Methods: Blood samples were collected from individuals for genomic DNA isolation. In order to see if these families had mutations in the SLC4A11 gene, we selected 11 microsatellite markers from the CHED2 candidate region and used them to genotype the families. DNA sequence analysis was used for mutation detection. Allele-specific PCR was used to determine the segregation of mutations in families and also to determine if the mutations were present in 100 ethnically matched normal control chromosomes.

Results: Haplotype analysis suggested linkage of the disorder to the CHED2 locus in both families. DNA sequence analysis showed a novel indel mutation, c.859_862delGAGAinsCCT (E287fsX21) in exon 8 of the SLC4A11 gene in one family. This mutation is predicted to truncate the protein with a lack of all 14 transmembrane domains. DNA sequence analysis of the second family showed a novel in-frame deletion mutation c.2014_2016delTTC or 2017_2019delTTC which will lead to the loss of a phenylalanine residue at position 672 or 673 (F672del or F673del). The mutant protein is expected to lack a conserved phenylalanine residue in transmembrane domain number 8.

Conclusions: This study reports two novel mutations in two CHED2 families and increases the spectrum of mutations in SLC4A11 to a total of 16. PCR-based screening methods were developed for both mutations for rapid screening of individuals.

Figure 1

Haplotype analysis of family 1. Haplotype analysis was carried out using 11 microsatellite markers. Disease haplotype is boxed. Note the affected individuals (III-3, III-5, and V-1) are homozygous for the disease haplotype. Individuals II-2, III-6, IV-6, IV-7, IV-8, and V-2 are heterozygous for the disease haplotype and are therefore carriers for the mutation. Empty squares and circles represent normal males and females, respectively. Filled squares and circles represent affected individuals. Affected individuals III-3, III-5, and V-1 are 42, 50, and 6 years old, respectively.

Figure 2

Haplotype analysis of family 2. Haplotype analysis was carried out using 11 microsatellite markers. Disease haplotype is boxed. Note the affected individuals (viz., III-1, III-3, III-5, IV-3, and IV-6) are homozygous for the disease haplotype. Whereas individuals II-3, IV-1, IV-5, IV-7, IV-8, V-3, and V-4 are heterozygous for the disease haplotype and are therefore carriers for the mutation. Empty squares and circles represent normal males and females, respectively. Filled squares and circles represent affected individuals. Affected individuals III-1, III-3, III-5, IV-3, and IV-6 are 70, 65, 45, 30, and 30 years old, respectively.

Figure 3

Mutation analysis of the SLC4A11 gene in family 1. A: Sequencing chromatogram of the exon 8 PCR product from the affected individual V-1. Normal DNA sequence is written on the top of the chromatogram. The deleted nucleotide residues "GAGA" is underlined in the normal sequence. Note deletion of GAGA and insertion of CCT (underlined) in the chromatogram. B: Agarose gel electrophoresis of PCR products from all individuals using wild-type (upper panel) and mutant allele-specific primer sets (lower panel). Note all normal individuals had bands in the upper panel as expected. All heterozygotes and patients had bands in the lower panel as expected. Lanes M and B stand for 100 bp marker and no template PCR, respectively. Individuals noted on top of the gel pictures are as in Figure 1. An asterisk marks the primer-dimer band.

Figure 4

Mutation analysis of the SLC4A11 gene in family 2. A: Sequencing chromatogram of the exon 15 PCR product from the affected individual IV-3. Normal DNA sequence is written on the top of the chromatogram. The tandem repeats of two "TTC" are underlined. Note only one TTC (underlined) in the chromatogram. B: Agarose gel electrophoresis of PCR products from all individuals using wild-type (upper panel) and mutant allele-specific primer sets (lower panel). All normal individuals have bands in the upper panel as expected. All heterozygotes and patients have bands in the lower panel as expected. Lanes M and B stand for 100 bp marker and no template PCR, respectively. Individuals noted on top of the gel pictures are as in Figure 2. An asterisk marks the primer-dimer band.