J Med Genet 41:468-473 doi:10.1136/jmg.2003.015792
  • Letters to JMG

An autosomal recessive cone–rod dystrophy associated with amelogenesis imperfecta

  1. M Michaelides1,2,
  2. A Bloch-Zupan3,4,
  3. G E Holder2,
  4. D M Hunt1,
  5. A T Moore1,2
  1. 1Institute of Ophthalmology, University College London, 11–43 Bath Street, London EC1V 9EL, UK
  2. 2Moorfields Eye Hospital, City Road, London EC1V 2PD, UK
  3. 3Department of Paediatric Dentistry, Eastman Dental Institute for Oral Health Care Sciences, University College London, 256 Gray’s Inn Road, London WC1X 8LD, UK
  4. 4Institute of Child Health, Developmental Biology Unit and Great Ormond Street Hospital for Children NHS Trust, 30 Guilford Street, London WC1N 1EH, UK
  1. Correspondence to:
 Professor A T Moore
 Institute of Ophthalmology, University College London, 11–43 Bath Street, London EC1V 9EL, UK;
  • Received 5 December 2003
  • Accepted 8 December 2003

The cone–rod dystrophies (CORDs) are a clinically and genetically heterogeneous group of progressive retinal disorders. They have similarities to the rod–cone or retinitis pigmentosa-type dystrophies, but can usually be distinguished on the basis of clinical findings and electrophysiology. The CORDs usually present with cone dysfunction related symptoms, including photophobia, poor colour vision, and reduced central visual function, but with time, poor night vision develops, reflecting rod photoreceptor involvement.

The age of onset in the CORDs is variable, but most patients present in the first 2 decades of life. CORD is usually an isolated finding; less commonly it may be associated with other systemic abnormalities, including dental anomalies. The CORD syndromes in which the causative gene or chromosomal locus has been identified are shown in table 1.

View this table:
Table 1

Syndromic cone–rod dystrophies (CORDs) with identified genes and known chromosomal loci

The association of CORD with amelogenesis imperfecta (AI) has been reported only once previously, in a large consanguineous Arabic family from the Gaza strip.12 AI is an inherited group of disorders of tooth enamel deposition affecting enamel structure, composition, and thickness, and can be broadly divided into the primarily hypoplastic (quantitative defect with thin or missing areas of enamel but otherwise normal in structure) and hypomineralised/hypomature (qualitative defect of normal thickness enamel but poorly mineralised) variants. However a new classification based on the molecular basis of the observed enamel phenotype will help to clarify the overlap in phenotypes that is commonly seen.13

The disorder in the Arabic family mapped to a 2 cM (5 Mb) region on chromosome 2q11, which includes the CNGA3 gene that encodes the α-subunit of the cGMP gated cation channel in cone photoreceptors.1 This represented a good candidate gene for this disorder because mutations in CNGA3 are associated with the cone dysfunction syndrome achromatopsia and with …