Abnormal crossing of the optic fibres shown by evoked magnetic fields in patients with ocular albinism with a novel mutation in the OA1 gene

Abstract

Aim: To perform genealogical and clinical studies in Finnish families with X linked ocular albinism (OA1), including characterisation of the potential misrouting of optic fibres by evaluating visual evoked magnetic fields (VEFs), and to determine the mutation behind the disease. Methods: Three families with OA1 were clinically examined. VEFs were measured in two affected males and in one female carrier to characterise the cortical activation pattern after monocular visual stimulation. The neuronal sources of the VEFs were modelled with equivalent current dipoles (ECDs) in a spherical head model. All coding exons of the OA1 gene were screened for mutations by single strand conformation analysis and direct polymerase chain reaction sequencing. Results: Genealogical studies revealed that the three families were all related. The affected males had foveal hypoplasia with reduced visual acuity varying from 20/200 to 20/50, variable nystagmus, iris transillumination, and hypopigmentation of the retinal pigment epithelium. The ECD locations corresponding to the VEFs revealed abnormal crossing of the optic fibres in both affected males, but not in the carrier female. A novel point mutation, leading to a STOP codon, was identified in the fifth exon of the OA1 gene. Conclusions:The data indicate that the novel mutation 640C.T in the OA1 gene is the primary cause of the eye disease in the family studied. VEFs with ECD analysis was successfully used to demonstrate abnormal crossing of the optic fibres.

Identification of a novel GPR143 mutation in a large Chinese family with congenital nystagmus as the most prominent and consistent manifestation

“…The achiasma syndrome has also been observed in a patient with nystagmus (Korff et al 2003). Misrouting of the optic fibers in some patients with ocular albinism has been revealed by use of visually evoked magnetic fields (VEFs) (Ohde et al 2004;Lauronen et al 2005). Functional magnetic resonance imaging (fMRI) studies of some patients with oculocutaneous albinism revealed abnormalities in the optic nerve head (Kasmann-Kellner et al 2003;Morland et al 2001).…”

The Prevalence of Attention-Deficit/ Hyperactivity Disorder Among Persons With Albinism

“…33 Findings in individuals with albinism using visual-evoked potential and magnetic resonance imaging studies are consistent with previous animal studies. 34,35 Children with ADHD alone may also have abnormal brain circuitry, especially in the prefrontal cortex, with secondary effects on behavior and visual-spatial working memory. 36 There are some limitations of this study.…”

Lyonization in ophthalmology

“…A three-lead visual evoked potential (VEP) shows a characteristic finding of reversed polarity (interhemispheric potential difference) due to abnormal decussation of retino-striate fibers passing through the optic chiasm [104][105][106][107][108][109][110]. In patients with ocular albinism, 75-85% of nerve fibers decussate to the contralateral side in contrast to 55% in normal individuals.…”