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BIPOSA Annual Meeting
Friday 06 October 2023, Royal Society of Medicine, London
09.45 Session II (S) (P)
Free papers
Moderators: Manoj Parulekar, Birmingham/Oxford and Rohit Jolly, London
27 Chiasmal misrouting in infantile nystagmus syndrome (INS): phenotypes in patients with molecular diagnoses
  1. MJ Gilhooley,
  2. M Moosajee,
  3. MM Neveu,
  4. M Theodorou
  1. Moorfields Eye Hospital and Institute of Ophthalmology, University College London, UK

Abstract

Chiasmal misrouting, once believed to be pathognomonic for albinism, has been reported in cases of INS, independent of melanin pathway disruption. The purpose of this study is to determine if there are clinical-electrophysiological parameters that correlate with particular genotypes in INS.

A retrospective chart review at Moorfields Eye Hospital identified 71 patients with a molecular diagnosis relating to INS. Visual acuity; presence of nystagmus, signs of albinism and OCT foveal hypoplasia grade were recorded alongside flash and pattern VEP (Visual Evoked Potential) amplitude and peak time. VEP asymmetry was assessed using the Pearson Correlation Coefficient (r).

Pathological variants in 8 genes (TYR, OCA2, HPS6, HPS3, HPS1, GPR143, FRMD7, SLC38A8, OCA1) were identified. Mean BCVA per group ranged from 0.38-0.74LogMAR F(0.72,3.5)=2.8; p=0.04 one-way ANOVA. All genotypes demonstrated foveal hypoplasia (mode grade 4) except FRMD7 (all grade 1). In this cohort, positive flash and pattern VEP amplitude/peak time asymmetry correlated with clinical signs of albinism (flash VEP, r=0.22(0-6yrs); pattern VEP, r=0.17(6-65yrs)). There was marked asymmetry in SLC38A8 patients (r = -0.85 to-0.93), a feature known to be associated with foveal hypoplasia 2.

This study provides a detailed genotype-phenotype correlation of VEP findings in a molecularly characterised INS cohort - useful in selecting clinically guided genetic testing and counselling patients

http://creativecommons.org/licenses/by-nc/4.0/

This is an open access article distributed in accordance with the Creative Commons Attribution Non Commercial (CC BY-NC 4.0) license, which permits others to distribute, remix, adapt, build upon this work non-commercially, and license their derivative works on different terms, provided the original work is properly cited, appropriate credit is given, any changes made indicated, and the use is non-commercial. See: http://creativecommons.org/licenses/by-nc/4.0/.

http://dx.doi.org/10.1136/bmjophth-2023-BIPOSA.27

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