Journal Article

Phenotypical characteristics of idiopathic infantile nystagmus with and without mutations in <i>FRMD7</i>

Shery Thomas, Frank A. Proudlock, Nagini Sarvananthan, Eryl O. Roberts, Musarat Awan, Rebecca McLean, Mylvaganam Surendran, A. S. Anil Kumar, Shegufta J. Farooq, Chris Degg, Richard P. Gale, Robert D. Reinecke, Geoffrey Woodruff, Andrea Langmann, Susanne Lindner, Sunila Jain, Patrick Tarpey, F. Lucy Raymond and Irene Gottlob

in Brain

Published on behalf of The Guarantors of Brain

Volume 131, issue 5, pages 1259-1267
Published in print May 2008 | ISSN: 0006-8950
Published online March 2008 | e-ISSN: 1460-2156 | DOI: http://dx.doi.org/10.1093/brain/awn046
Phenotypical characteristics of idiopathic infantile nystagmus with and without mutations in FRMD7

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Idiopathic infantile nystagmus (IIN) consists of involuntary oscillations of the eyes. The familial form is most commonly X-linked. We recently found mutations in a novel gene FRMD7 (Xq26.2), which provided an opportunity to investigate a genetically defined and homogeneous group of patients with nystagmus. We compared clinical features and eye movement recordings of 90 subjects with mutation in the gene (FRMD7 group) to 48 subjects without mutations but with clinical IIN (non-FRMD7 group). Fifty-eight female obligate carriers of the mutation were also investigated. The median visual acuity (VA) was 0.2 logMAR (Snellen equivalent 6/9) in both groups and most patients had good stereopsis. The prevalence of strabismus was also similar (FRMD7: 7.8%, non-FRMD7: 10%). The presence of anomalous head posture (AHP) was significantly higher in the non-FRMD7 group (P < 0.0001). The amplitude of nystagmus was more strongly dependant on the direction of gaze in the FRMD7 group being lower at primary position (P < 0.0001), compared to non-FRMD7 group (P = 0.83). Pendular nystagmus waveforms were also more frequent in the FRMD7 group (P = 0.003). Fifty-three percent of the obligate female carriers of an FRMD7 mutation were clinically affected. The VA's in affected females were slightly better compared to affected males (P = 0.014). Subnormal optokinetic responses were found in a subgroup of obligate unaffected carriers, which may be interpreted as a sub-clinical manifestation. FRMD7 is a major cause of X-linked IIN. Most clinical and eye movement characteristics were similar in the FRMD7 group and non-FRMD7 group with most patients having good VA and stereopsis and low incidence of strabismus. Fewer patients in the FRMD7 group had AHPs, their amplitude of nystagmus being lower in primary position. Our findings are helpful in the clinical identification of IIN and genetic counselling of nystagmus patients.

Keywords: X-linked idiopathic infantile nystagmus; FRMD7; obligate carrier; clinical characteristics; eye movements

Journal Article.  5286 words.  Illustrated.

Subjects: Neurology ; Neuroscience

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