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The authors have studied skin color modifications in 3 cases of phenylketonuria and have observed the characteristic changes; fair skin and fair hair. In addition they noted hundred of pigmented pin point or slightly larger patches in the two more affected patients, in the areas exposed to sunshine. With regard to the ultrastructural study of the epidermis basal layer, the proportion of melanocytes in the two most severe cases was slightly higher than in the normal skin of 6 control subjects. Langerhans cells could not be acertained. The more severe was the disease the greater was the tendency for a lower proportion of keratinocytes containing melanin. There is a certain parallelism between the skin color modifications the biochemical examinations (blood level of phenylalanin and tyrosine) and the ultrastructural changes. The higher the blood level of phenlalanine and/or the more pronounced the disorders of skin color, the more evident would be the ultrastructural changes: higher proportion of melanocytes that usually do not produce the melanosomes, and lower percentage of keratinocytes with melanin. On the other hand, the ultrastructure of the basal layer would suggest the seriousness of clinical manifestations and/or the intesity of the metabolic error.

To avoid any bias, the ultramicroscopic examination was performed by the morphologist without knowing whether the material examined was from the vitiligo patch or from the marginal hyperpigmented and normal skin. Only at the end of the investigation, he was informed about the code of the material. He had also been informed about the possibility of receiving skin biopsies from a patient without vitiligo, what in fact was done with the inclusion of one case of albinism. Six cases of vitiligo have been studied. The melanocytes usually have not been observed in the vitiligo patches, where a variable number of Langerhans cells were seen. In the melanocytes reached about 17 p. 100 of the cellular population; Langerhans cells were absents. In the marginal normal skin the average proportion of melanocytes was near 10 p. 100 of the cellular population and the Langerhans have been observed only in one case (1.8 p. 100 of the population). Regarding the keratinocytes of the marginal hyperpigmented and normal skin, respectively 75 p. 100 and 59 p. 100 contained melanin; in the vitiligo patches only in one case keratinocytes contained melanin (2.8 p. 100 of the keratinocytes population as an average).