A comparison of clinical and eye movement characteristics between albinism and idiopathic infantile nystagmus with and without mutations in the FRMD7 gene

Abstract

Abstract Purpose Nystagmus consists of involuntary to and fro oscillations of the eyes. The differences between nystagmus associated with albinism and idiopathic infantile nystagmus (IIN) are unclear. Recently mutations in a novel gene called FRMD7 have been found to underlie a significant proportion of X‐linked IIN. Phenotypic variations in eye movements between FRMD7 and non‐FRMD7 types have also been recently described. We have compared clinical and eye movement characteristics between albinism and IIN with and without mutations in the FMRD7 gene. Methods Clinical features and eye movement were recorded from 37 albino subjects, 83 subjects with the FRMD7 mutation and 45 subjects without the FRMD7 mutation. Results Mean visual acuity was significantly worse in albinos compared to IIN patients (p<<0.0001). Although there was no significant differences between the groups (p>0.05) for nystagmus amplitude or foveation, the frequency of nystagmus was significantly slower in albinism (p<<0.0001). In addition, nystagmus associated with albinism was significantly more likely to be jerk nystagmus rather than pendular nystagmus compared to FRMD7 group (p<<0.0001). The most common waveform associated with albinism was pure jerk nystagmus, whereas non‐FRMD7 was more likely to be associated with jerk with extended foveation. Conclusion Contrary to available literature, nystagmus associated with albinism shows distinct differences to IIN both with and without FRMD7 mutations. This suggests the possibility of different underlying mechanisms to albinism and IIN in generating eye oscillations although these are yet to be elucidated