X-LINKED PROGRESSIVE CONE DYSTROPHY

Six affected males, three female carriers, and two possible carriers w ere evaluated from a three generation pedigree with X linked progressi ve cone dystrophy. The affected males presented with progressive decre ase of visual acuity, impairment of colour vision, and deterioration o f electroretinogram, which ranged from absent response to red light in all young patients to abnormal cone-rod responses in the elderly ones . In most affected males dark adaptation curves were monophasic and th e electro-oculogram values were reduced. While some obligate carriers showed functional anomalies, they ah had reduced electroretinogram res ponse to red light. The a(1)/a(T) ratio for I joule white light was an appropriate indicator for carrier state. The family was studied with seven DNA markers from the proximal part of the short arm of the human X chromosome. So far, significant linkage has been found between thre e DNA markers and COD1, which assigns the progressive cone dystrophy g ene (COD1) in this family to Xp21-p11.1. Differential diagnosis with c ongenital cone dystrophies is discussed.