Cone dystrophy or macular dystrophy associated with novel autosomal dominant GUCA1A mutations

Sixteen different mutations in the guanylate cyclase activator 1A gene (GUCA1A), have been previously identified to cause autosomal dominant cone dystrophy (adCOD), cone-rod dystrophy (adCORD), macular dystrophy (adMD), and in an isolated patient, retinitis pigmentosa (RP). The purpose of this study is to report on two novel mutations and the patients' clinical features.

Clinical investigations included visual acuity and visual field testing, fundus examination, high-resolution spectral-domain optical coherence tomography (OCT), fundus autofluorescence imaging, and full-field and multifocal electroretinogram (ERG) recordings. GUCA1A was screened by Sanger sequencing in a cohort of 12 French families with adCOD, adCORD, and adMD.

We found two novel GUCA1A mutations-one amino acid deletion, c.302_304delTAG (p.Val101del), and one missense mutation, c.444T>A (p.Asp148Glu)-each of which was found in one family. The p.Asp148Glu mutation affected one of the Ca²⁺-binding amino acids of the EF4 hand, while the p.Val101del mutation resulted in the in-frame deletion of Valine-101, localized between two Ca²⁺-binding aspartic acid residues at positions 100 and 102 of the EF3 hand. Both families complained of visual acuity loss worsening with age. However, the p.Asp148Glu mutation was present in one family with adCOD involving abnormal cone function and an absence of macular atrophy, whereas p.Val101del mutation was encountered in another family with adMD without a generalized cone defect.

The two novel mutations described in this study are associated with distinct phenotypes, MD for p.Val101del and COD for p.Asp148Glu, with no intrafamilial phenotypic heterogeneity.