With 8 figures
Investigations of heredity in congenital achromatopsia have indicated an autosomal recessive type of inheritance (FRANCOIS, VERRIEST & DE ROUC~:, 1955). The pedigree reported here is unique in that it is characterized by an X-linked recessive mode of inheritance (OeITz & SPIVEY). Therefore, we have had the opportunity to study the carrier state in this uncommon condition (Fig. 1).
The affected family members studied have the following characteristics in common: low visual acuity (6/60); myopia; reduction in the maximum of the photopic spectral sensitivity curve indicated by the Nagel anomaloscope; fine pendular nystagmus in the children; mild light avoidance with reduction of visual acuity in intense illumination; mild pigmentary abnormalities of the macula; poor binocular cooperation; central scotoma under photopic illumination; typical achromatic responses with the Nagel anomaloscope (Fig. 2); absence of the photopic ERG response and reduced photopic CFF; abnormal biphasic dark adaptation curve; and a typical achromatic response with the Sloan Achromatopsia Test.
Three carrier females were examined. In each instance the validity of the carrier state was established by the examination of affected offspring. Xg(a) blood linkage studies have definitely placed the responsible gene on the X chromosome. The visual acuity of each carrier was normal. There were no ocular abnormalities noted by the usual methods of examination.