Hair colour is one of the most conspicuous phenotypes in humans, ranging from black, brown, blond to red. This diversity arises mostly from the quantity and ratio of the black-dark brown
eumelanin and the reddish-brown
pheomelanin. To study the chemical basis underlying the diversity of hair colour, we have developed several chemical methods to quantify those two pigments. Alkaline H(2) O(2) oxidation affords
pyrrole-2,3,5-tricarboxylic acid (PTCA) as a
eumelanin marker and thiazole-2,4,5-tricarboxylic
acid (
TTCA) as a
pheomelanin marker.
Pheomelanin can also be analysed as
4-amino-3-hydroxyphenylalanine (4-AHP) after
hydroiodic acid hydrolysis. Using those methods, we evaluated the contents of
eumelanin and
pheomelanin (the 'chemical' phenotype) in human hairs of black, dark brown, brown, light brown, blond and red colour (the 'visual' phenotype).
Eumelanin contents decrease in that order, with a trace but constant level of
pheomelanin, except for red hair which contains about equal levels of
pheomelanin and
eumelanin. Thus, the chemical phenotype correlates well with the visual phenotype. The genotype of
melanocortin-1 receptor (MC1R), a gene regulating the red hair phenotype, is predictive of hair
melanin expressed as the log value of
eumelanin to
pheomelanin ratio, with a dosage effect evident. Hair
melanin contents were also analysed in patients with various hypopigmentary disorders including
Hermansky-Pudlak syndrome,
Menkes disease,
proopiomelanocortin deficiency,
cystinosis,
malnutrition and trace
metal deficiency. The chemical phenotype helped evaluate the precise effects of each disease on pigmentation. In studies of human hair, the chemical phenotype will find more and more application as an objective measure of pigmentation.