Hypertyrosinaemia

Screening tests of tyrosine levels in the newborn population showed that an elevated blood tyrosine level is the second commonest, and diagnostically the most serious, problem of neonatal age. Almost 1% of all newborn infants have a raised tyrosine level. The classic form of tyrosinosis and secondary hypertyrosinaemia in particular must be differentiated from benign, transitory forms. Methods for a differential diagnosis after loading the organism with ascorbic acid, pyridoxine or folic acid have been described. L-tyrosine tolerance tests proved ineffective. The results of the dietary treatment of transitory and classic forms of hypertyrosinaemia, using phenylalanine- and tyrosine-free hydrolysates, are described. The incidence of these diseases at different ages is shown in a table. Study of psychomotric development shows that untreated children do not display a subnormal IQ until they are of pre-school or school age.