Brain Advance Access originally published online on March 27, 2008
Brain 2008 131(5):1259-1267; doi:10.1093/brain/awn046
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Phenotypical characteristics of idiopathic infantile nystagmus with and without mutations in FRMD7
1University of Leicester, Ophthalmology group, PO Box 65, Leicester, LE2 7LX, 2University Hospitals of Leicester, Department of Ophthalmology, 3University Hospitals of Leicester, Department of Medical Physics, Leicester, LE1 5WW, 4Department of Ophthalmology, Leeds General Infirmary, Leeds, LS2 9NS, UK, 5Foerderer Eye Movement Centre for Children, Wills Eye hospital, Philadelphia, 19107, USA, 6Medical University Graz, Department of Ophthalmology, Auenbruggerplatz 4, Graz, Austria, 7Royal Preston Hospital, Sharoe Green Lane North, Preston, Lancashire, PR2 9HT, 8Wellcome Trust Sanger Institute, Hinxton, Cambridge, CB10 1SA and 9Cambridge Institute of Medical Research, Addenbrooks Hospital, Cambridge, CB2 2XY, UK
Correspondence to: Prof. Irene Gottlob, Ophthalmology Group, University of Leicester, Faculty of Medicine & Biological Sciences, Robert Kilpatrick Clinical Sciences Building, Leicester Royal Infirmary, PO Box 65, Leicester, LE2 7LX, UK E-mail: ig15{at}le.ac.uk
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.
Key Words: X-linked idiopathic infantile nystagmus; FRMD7; obligate carrier; clinical characteristics; eye movements
Abbreviations: AHP, anomalous head posture; IIN, idiopathic infantile nystagmus; OKN, optokinetic nystagmus; VA, visual acuity
Received December 16, 2007. Revised February 11, 2008. Accepted February 20, 2008.