Five novel CNGB3 gene mutations in Polish patients with achromatopsia

Abstract

Purpose: To identify the genetic basis of achromatopsia (ACHM) in four patients from four unrelated Polish families.

Methods: In this study, we investigated probands with a clinical diagnosis of ACHM. Ophthalmologic examinations, including visual acuity testing, color vision testing, and full-field electroretinography (ERG), were performed in all patients (with the exception of patient p4, who had no ERG). Direct DNA sequencing encompassing the entire coding region of the CNGB3 gene, eight exons of the GNAT2 gene, and exons 5-7 of the CNGA3 gene was performed. Segregation analysis for the presence and independent inheritance of two mutant alleles was performed in the three families available for study.

Results: All patients showed typical achromatopsia signs and symptoms. Sequencing helped detect causative changes in the CNGB3 gene in all probands. Eight different mutations were detected in the CNGB3 gene, including five novel mutations: two splice site mutations (c.1579-1G>A and c.494-2A>T), one nonsense substitution (c.1194T>G), and two frame-shift mutations (c.393_394delGCinsTCCTGGTGA and c.1366delC). We also found three mutations: one splice site (c.1578+1G>A) and two frame-shift deletions that had been previously described (c.819_826del and c.1148delC). All respective parents were shown to be heterozygous carriers for the mutation detected in their children.

Conclusions: The present study reports five novel mutations in the CNGB3 gene, and thus broadens the spectrum of probably pathogenic mutations associated with ACHM. Together with molecular data, we provide a brief clinical description of the affected individuals.

Figure 1

Pedigrees and genotyping results of families with achromatopsia. The genotypes are provided for all subjects available for molecular genetic analysis. The black square and the circles represent affected male and females, respectively. White squares and circles represent unaffected family members. A triangle indicates miscarriage, and a rhombus indicates ongoing pregnancy in family 3. Arrows point to probands.

Figure 2

ERG of p2. A: Photopic white flash electroretinogram (ERG) shows non-recordable response. B: Scotopic white flash ERG shows normal response. C: Photopic white 30 Hz flicker shows flat response. 1-L indicates the left eye; 2-R indicates the right eye.

Figure 3

Chromatograms showing eight mutations identified in the CNGB3 gene in patients with ACHM. A: Sequence trace of part of intron 13 in an affected individual p1 carrying a heterozygous mutation c.1578+1G>A (upper panel) and a normal control individual (lower panel). B: Part of intron 13 in an affected individual p1 carrying a heterozygous mutation c.1579–1G>A (upper panel) and a normal control individual (lower panel). C: Part of exon 6 in an affected individual p2 carrying a heterozygous mutation c. 819_826del (upper panel) and a normal control individual (lower panel). D: Part of exon 11 in an affected individual p2 carrying a heterozygous mutation c.1194T>G (upper panel) and a normal control individual (lower panel). E: Part of exon 4 in an affected individual p3 carrying a heterozygous mutation c.393_394delGCinsTCCTGGTGA (upper panel) and a normal control individual (lower panel). F: Part of intron 4 in an affected individual p3 carrying a heterozygous mutation c.494–2A>T (upper panel) and a normal control individual (lower panel). G: Part of exon 10 in an affected individual p4 carrying a heterozygous mutation c.1148delC (upper panel) and a normal control individual (lower panel). H: Part of exon 12 in an affected individual p4 carrying a heterozygous mutation c.1366delC (upper panel) and a normal control individual (lower panel).