Oligocone trichromacy: clinical and molecular genetic investigations.
OBJECTIVE
To describe the phenotype and genotype of patients with a diagnosis of oligocone trichromacy (OT).


METHODS
Six unrelated patients had a detailed ophthalmic examination including color vision testing, a Goldmann visual field test, fundus photography, and full-field electroretinography (ffERG). Five patients also underwent multifocal (mf)ERG, autofluorescence recording, and optical coherence tomography (OCT). Genetic analysis included sequencing of all coding regions and flanking introns of CNGA3, CNGB3, GNAT2, KCNV2, and PDE6C.


RESULTS
All patients had subnormal visual acuity, a history of congenital nystagmus, and subjectively normal or near-normal color vision; five patients reported photophobia. Clinical examinations revealed largely normal fundi, normal Goldmann visual field results with the IV/4e target, and normal color discrimination or mild color vision deficiency. Electrophysiological investigations showed either complete absence of recordable cone responses or severely reduced amplitudes. All retinal layers were identifiable by OCT, which also showed thinning of the peripheral retina. Genetic analysis revealed two causative CNGB3 mutations in one patient and single heterozygous mutations of unknown significance in CNGB3 and PDE6C in two other patients.


CONCLUSIONS
Oligocone trichromacy is a heterogeneous condition with respect to both phenotypic appearance and genetic background. The finding of mutations in genes known to be involved in complete and incomplete achromatopsia supports the notion that some forms of OT is an extreme form of incomplete achromatopsia with preferential loss of peripheral cones.
National Eye Clinic, Kennedy Center, Glostrup, Denmark.
Mette K G
MK
Andersen
Nynne L B
NL
Christoffersen
Birgit
B
Sander
Carsten
C
Edmund
Michael
M
Larsen
Tanja
T
Grau
Bernd
B
Wissinger
Susanne
S
Kohl
Thomas
T
Rosenberg
D000328:Adult; D002648:Child; D003119:Color Perception Tests; D055253:Color Vision / Q000502:physiology; D003117:Color Vision Defects / Q000175:diagnosis / Q000235:genetics*; D054707:Cyclic Nucleotide Phosphodiesterases, Type 6 / Q000235:genetics; D054815:Cyclic Nucleotide-Gated Cation Channels / Q000235:genetics; D004252:DNA Mutational Analysis; D004596:Electroretinography; D015785:Eye Diseases, Hereditary / Q000175:diagnosis / Q000235:genetics*; D005136:Eye Proteins / Q000235:genetics; D005260:Female; D005451:Fluorescein Angiography; D051960:GTP-Binding Protein alpha Subunit, Gi2 / Q000235:genetics; D005838:Genotype; D006801:Humans; D008297:Male; D008875:Middle Aged; D020417:Nystagmus, Congenital / Q000235:genetics; D010641:Phenotype; D016133:Polymerase Chain Reaction; D012150:Polymorphism, Restriction Fragment Length; D024642:Potassium Channels, Voltage-Gated / Q000235:genetics; D017949:Retinal Cone Photoreceptor Cells / Q000473:pathology*; D012164:Retinal Diseases / Q000175:diagnosis / Q000235:genetics*; D041623:Tomography, Optical Coherence; D014792:Visual Acuity; D014794:Visual Fields / Q000502:physiology
C518238:CNGA3 protein, human; C415904:CNGB3 protein, human; D054815:Cyclic Nucleotide-Gated Cation Channels; D005136:Eye Proteins; C489610:KCNV2 protein, human; D024642:Potassium Channels, Voltage-Gated; D054707:Cyclic Nucleotide Phosphodiesterases, Type 6; C096885:PDE6C protein, human; C498015:GNAI2 protein, human; D051960:GTP-Binding Protein alpha Subunit, Gi2