Evaluation of hairbulb incubation test and tyrosinase assay in the classification of albinism

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Abstract
Hairbulb tests and tyrosinase assays were performed in 88 albinos, 59 obligate heterozygotes and 54 normal controls. Our findings suggest that the classification of albinism is more complicated than previously assumed. An improved classification system is important for genetic counseling as there is evidence for the existence of two different autosomal non-allelic genes for OCA (Witkop et al, 1970; Nance et al., 1971). Our results indicate that the hairbulb test alone is insufficient for classifying albinos, i.e. detecting two genotypes. the hairbulb test, tyrosinase activity, hair color and the ability of the skin to tan do not parallel in all cases. We tried to classify the albinos phenotypically and biochemically, the latter into five groups: four according to the hairbulb test, a fifth group consisted of XOA. Tyrosinase assays demonstrate that the values range from zero to low in our TN and T ± groups; from zero to high in our TP+, TP and XOA groups. the latter values overlap with those of the controls and the heterozygotes. Because of this overlap we found that it is not possible to detect heterozygotes for TNOCA. Our doubts regarding the existence of the YM and the AROA variant are discussed. Comparing our data with those for the USA and the UK we found a difference in frequency of TNOCA in the Netherlands, i.e., five times less than expected.