Visual evoked potentials in Prader-Willi syndrome

Oculocutaneous, electrophysiological, and cytogenetic factors were evaluated in 14 patients with Prader-Willi syndrome and in three controls, two albinos and a normal observer. In a substantial number of PW patients chromosomal anomalies, particularly deletions of the long arm of chromosome 15 as well as hypopigmentation of hair, skin, and eye have been identified. In the genetic condition of albinism, hypopigmentation related to neural ectoderm derivatives is associated with reduced visual acuity, foveal hypoplasia, and aberrant retinogeniculocortical projections. The latter can be observed by visual evoked potential (VEP) assessment of hemispheric response symmetry. To determine the possible neural ectodermal origin of hypopigmentation and its involvement in ocular development and optic pathway integrity, the potential distributions of the pattern onset/offset VEP were examined. Our results show hypopigmentation in 13 of our 14 PW patients and a chromosome abnormality in 6; no correlation between these two features was found. None of the PW patients showed the characteristic contralateral hemispheric asymmetry seen in albinism. On the other hand their VEP profiles were found to be atypical, rendering waveform and cortical topography difficult to interpret. Analysis suggests that in the absence of VEP evidence for optic pathway misprojection, PW hypopigmentation is probably of neural crest origin.