Clinicopathologic effects of the Q64ter rhodopsin mutation in retinitis pigmentosa

To correlate retinal histopathology with functional changes caused by the rhodopsin Q64ter mutation.

A 50-year-old female heterozygote was evaluated clinically and with psychophysical and electroretinographic measurements of rod and cone function. The retinas obtained after death were examined microscopically, including immunolabeling with antibodies against the C- and N-termini of rhodopsin.

On clinical examination 4 months before death, patient's acuity was 20/60, and she had midperipheral scotomas with retained function centrally and in the far periphery. The rod electroretinogram (ERG) was undetectable, and the cone ERG was reduced in amplitude with abnormal receptoral and postreceptoral responses. A previous study of the phenotype of mildly affected family members of the donor suggested that the rod outer segments (ROS) were shortened and that only wild-type rhodopsin was functional. The retinas contained only scattered cones in the midperiphery; the maculas and far peripheral regions contained reduced numbers of rods and cones with short to absent outer segments. The ROS appeared to contain wild-type, but not mutant, rhodopsin, and many peripheral rods had sprouted long rhodopsin-positive neurites that projected into the inner retina. Many cone synapses were abnormal, and the axons of some peripheral cones reached the inner plexiform layer.

Microscopic changes in the donor retinas correlated well with the abnormalities in visual function in the patient donor and other family members. Postreceptoral ERG defects may relate to the abnormal photoreceptor processes found in the inner retina.