PubMed · 11462380
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M Nakamura. 2001. [Albinism].. https://pubmed.ncbi.nlm.nih.gov/11462380/
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Type I oculocutaneous albinism (OCA) is an autosomal recessive disorder caused by the reduction or the absence of tyrosinase (TYR) activity in melanocytes of the skin, hair and eyes. Here we report an analysis of 45 patients with OCA. We found five novel mutations in the tyrosinase gene involved in the pathogenesis of oculocutaneous albinism type IA or type IB (OCA-1A/B) in five unrelated patients. Three mutations are missense mutations (G109R, P205T and H256Y) and two are nucleotide deletions (336-337delCA and 678-680delAGG). One patient is homozygous for the previously known V275F mutation but has an extremely mild OCA phenotype and has no eye features typical of OCA. In several patients we discovered only one or even no mutation in the coding sequence of the TYR gene. Thus, this disease may also result from mutations in non coding regions of the gene or in another gene involved in the biosynthesis of melanin. Hum Mutat 17:352, 2001.
Albino mammals show very characteristic deficits in their optokinetic system, and albino ferrets are even optokinetically blind. To investigate the neuronal causes for this defect we compared the morphology of retinal slip cells in the pretectal nucleus of the optic tract and the dorsal terminal nucleus of the accessory optic system (NOT-DTN) in pigmented and albino ferrets (Mustela putorius furo) using retrograde tracing techniques. After tracer injections into the inferior olive, equal numbers of NOT-DTN neurons were retrogradely labelled in pigmented and albino animals. However, NOT-DTN cells in albino ferrets had fewer stem dendrites, and the cumulative dendritic length was reduced by 30% when compared with NOT-DTN neurons in pigmented animals. In addition, the prominent network formed by distal dendrites observed in the NOT-DTN of pigmented ferrets was largely diminished in albinos. Taken together with behavioural and physiological data, these findings indicate that the NOT-DTN as the main visuomotor interface in the optokinetic system is clearly defective in albino ferrets.
The representation of the visual field in early visual areas is retinotopic. The point-to-point relationship on the retina is therefore maintained on the convoluted cortical surface. Functional magnetic resonance imaging (fMRI) has been able to demonstrate the retinotopic representation of the visual field in occipital cortex of normal subjects. Furthermore, visual areas that are retinotopic can be identified on computationally flattened cortical maps on the basis of positions of the vertical and horizontal meridians. Here, we investigate abnormal retinotopic representations in human visual cortex with fMRI. We present three case studies in which patients with visual disorders are investigated. We have tested a subject who only possesses operating rod photoreceptors. We find in this case that the cortex undergoes a remapping whereby regions that would normally represent central field locations now map more peripheral positions in the visual field: In a human albino we also find abnormal visual cortical activity. Monocular stimulation of each hemifield resulted in activations in the hemisphere contralateral to the stimulated eye. This is consistent with abnormal decussation at the optic chiasm in albinism. Finally, we report a case where a lesion to white matter has resulted in a lack of measurable activity in occipital cortex. The activity was absent for a small region of the visual field, which was found to correspond to the subject's field defect. The cases selected have been chosen to demonstrate the power of fMRI in identifying abnormalities in the cortical representations of the visual field in patients with visual dysfunction. Furthermore, the experiments are able to show how the cortex is capable of modifying the visual field representation in response to abnormal input.