Histidinemia was detected in a Negro girl through a multiple screening process which selected out families having more than one child with learning disorders. Studies of 18 randomly selected asymptomatic Negro children failed to demonstrate a significant racial variation in blood histidine levels; the mean for the group studied was 0.92 mg/100 ml compared to a range of 0.49 to 1.66 mg/100 ml previously recorded among populations of mixed racial origin.
Kappelman M, Thomas GH, Howell RR. Histidinemia in a Negro Child. Am J Dis Child. 1971;122(3):212-214. doi:10.1001/archpedi.1971.02110030068005