SLC6A19 and phenylketonuria: While both genetic loss of Slc6a19 function (14) and JN-170 were shown to lower plasma Phe in Pahenu2 mice with highly elevated baseline Phe levels (> 1,200 μM), interindividual variability in plasma Phe is high in patients with PKU, and 38% of adult patients with PKU have plasma Phe levels that are elevated but are under 1,200 μM (24).