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‘Cone dystrophy with supranormal rod response’ in children
  1. Arif O Khan1,2,
  2. May Alrashed2,3,4,
  3. Fowzan S Alkuraya2,5,6
  1. 1Division of Pediatric Ophthalmology, King Khaled Eye Specialist Hospital, Riyadh, Saudi Arabia
  2. 2Department of Genetics, King Faisal Specialist Hospital and Research Center, Riyadh, Saudi Arabia
  3. 3Department of Clinical Laboratory Sciences, College of Applied Medical Sciences, King Saud University, Riyadh, Saudi Arabia
  4. 4Department of Molecular Genetics, UCL Institute of Ophthalmology, London, UK
  5. 5Department of Pediatrics, King Khalid University Hospital and College of Medicine, King Saud University, Riyadh, Saudi Arabia
  6. 6Department of Anatomy and Cell Biology, College of Medicine, Alfaisal University, Riyadh, Saudi Arabia
  1. Correspondence to Dr Arif O Khan, Division of Pediatric Ophthalmology, King Khaled Eye Specialist Hospital, Riyadh 11462, Saudi Arabia; arif.khan{at}mssm.edu

Abstract

Aim To describe the initial clinical presentation of children with ‘cone dystrophy with supranormal rod response,’ a distinct retinal disorder from recessive KCNV2 mutations.

Methods Retrospective case series.

Results Nine children (seven families) initially examined from 2 to 8 years of age were identified. Three had a similar initial presentation of abnormal head position with head shaking and nystagmus, while the other six presented with either infantile nystagmus (without abnormal head position or head shaking), suspected congenital glaucoma (with associated nystagmus), intermittent exotropia, V-pattern esotropia, comitant esotropia or difficulty with near vision only (reading). Only two children had clinically evident retinal changes (macular discoloration), and only two had a myopic cycloplegic refraction (the child with infantile nystagmus and the glaucoma suspect who actually had megalocornea). In addition to cone dystrophy, ERGs showed delayed scotopic responses with supranormal (six), high normal (two) or normal (one) scotopic b-wave responses to bright flash. Only one ERG (with a supranormal response) did not show a broad a-wave trough response to scotopic flash. For all patients, KCNV2 sequencing revealed one of three homozygous recessive mutations (one previously reported (p.E143X), two novel (p.Y53X, p.E80D)). The three children who presented with an abnormal head position, head shaking and nystagmus and the child who presented with infantile nystagmus had several years' follow-up, during which these findings resolved (two) or decreased (two).

Conclusions Initial clinical presentation varied, the most common presentation being abnormal head position, head shaking and nystagmus that improved with time. ERG findings are characteristic and specific for KCNV2 mutations but do not necessarily include a scotopic b-wave flash response that is supranormal under standard ERG conditions.

  • Cone dystrophy
  • supranormal rod response
  • KCNV2
  • pediatric
  • nystagmus
  • Genetics
  • Child health (paediatrics)

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Footnotes

  • Funding This study was funded in part by King Abdulaziz City for Science and Technology 08-MED497-20 (FSA).

  • Competing interests None.

  • Patient consent Obtained.

  • Ethics approval Ethics approval was provided by the IRB of King Faisal Specialist Hospital and Research Center, King Khaled Eye Specialist Hospital.

  • Provenance and peer review Not commissioned; externally peer reviewed.

  • Data Sharing Statement The corresponding author had access to data and confirms its accuracy.

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