Identification of two novel OPA1 mutations in Chinese families with autosomal dominant optic atrophy

Abstract

Purpose: To report the clinical features and identification of two novel mutations in two Chinese pedigrees with autosomal dominant optic atrophy (ADOA).

Methods: Two families (F1 and F2) including ten affected members and nine unaffected family individuals were examined clinically. After informed consent was obtained, peripheral blood samples of all the participants were obtained, and genomic DNA was extracted. Linkage analysis was performed with two microsatellite markers around the OPA1 gene (D3S2305 and D3S3562) in family F1. The coding region (exon 1-28), including intron-exon boundary of the OPA1 gene, were screened in the 2 families by polymerase chain reaction (PCR) and direct DNA sequencing. Whenever substitutions were identified in a patient, single strand conformation polymorphism (SSCP) analysis was performed on all available family members and 100 normal controls. To characterize a splicing site mutation, RT-PCR of total RNA of leukocytes obtained from three patients and seven unaffected individuals of family F1 was performed with the specific primers.

Results: The affected individuals all presented with bilateral visual failure and temporal or total pallor of the optic discs. Genotyping of family F1 revealed the linkage to the OPA1 gene on 3q28-29. After sequencing of OPA1 gene, a novel heterozygous splicing site mutation c.985 -2A>G in intron 9 was found in family F1. RT-PCR result showed the skipping of the exon 10 in the mutant transcript, which results in loss of 27 amino acids in the OPA1 protein. A novel heterozygous nonsense mutation c.2197C>T(p.R733X)was detected in family F2.

Conclusions: Our findings expand the spectrum of OPA1 mutations and further established the role of OPA1 gene in Chinese patients with ADOA.

Figure 1

Family structure and haplotype analysis of the two Chinese families with ADOA. Pedigree of the two families with autosomal dominant optic atrophy (ADOA) and haplotype analysis of the family F1 showed segregation two microsatellite markers on chromosome 3 listed in descending order from the centromeric end. Squares indicate males; circles indicate females; slashed symbols indicate deceased; solid symbols indicate affected; open symbols indicate unaffected; and arrow symbol indicates proband.

Figure 2

Fundus appearance of a patient with autosomal dominant optic atrophy (ADOA). Fundus of proband of family F2 showed bilateral temporal pallor of optic discs.

Figure 3

Direct sequencing analysis of the coding region of the OPA1 gene. A. Sequence shows the heterozygous splicing site mutation c.985–2A>G; B: Sequence shows the heterozygous nonsense mutation c.2197C>T (p. R733X). The 2 sequences given are in sense direction.

Figure 4

RT–PCR and direct sequencing analysis for the splice site mutation c.985–2A>G. A: Ethidium bromide-agarose gel was loaded with RT–PCR products generated from leukocytes of total RNA of three affected members (two bands) and seven unaffected individuals (one band) of family F1. B and C: The sequence chromatograms of the two bands from the patient’s RT–PCR products; B: The mutant transcript sequence with the skipping exon 10. C: The corresponding normal transcript sequence between exon 9 and exon 11.