OBJECTIVETo investigate the incidence of hyperphenylalaninemia (HPA) caused by different etiologic factors in China and the relationship between the phenylalanine and mental development of patients with HPAs who were diagnosed by neonatal screening and early treated.

METHODSTwo hundred and twenty-three patients with HPA detected by neonatal screening programs were refered to us at the age of (41 +/- 27) days after birth. The differential diagnosis was performed by BH(4) (20 mg/kg) loading test, urinary pterin analysis and dihydropteridine reductase (DHPR) activity determination respectively. The control of phenylalanine (Phe) metabolism, growth and mental development were evaluated in all treated patients. Related gene mutation analysis was performed in some patients

RESULTSOne hundred and twenty-nine of 223 patients (57.8%) were diagnosed as phenylalanine hydroxylase deficiency (PAHD), 64 patients (28.7%) as BH(4) responsive PAHD, 30 patients (13.5%) as 6-pyruvoyl tetrahydropterin synthase deficiency (PTSD). One hundred and forty-nine patients were followed at age of 4 m - 2 y in our clinic. The 136 of 149 patients were treated according to different etiology at the age of 1.6 m (0.5 - 3.5 m) after birth. Thirteen patients were followed up without the need for treatment. All patients had normal growth development. One hundred and eight (79.4%) of 136 treated patients had normal mental development. The negative correlation (r = -0.439, P < 0.01) between IQ and average Phe levels were observed in 58 patients. Twenty-eight patients were able to go to primary school or even university. Nine kinds of PTS gene mutations were found in 9 cases with PTSD, among which 286G-->A and 259C-->T were most commonly seen, accounting for 45%. Seven kinds of PAH gene mutations were found in 13 cases with BH(4) responsive PAHD with the R241C (43.8%) mutation being the most frequent one.

CONCLUSIONThe differential diagnosis should be quickly made in all HPA patients detected by neonatal screening. Near 80% patients early treated had normal mental development. The good control of blood Phe level is a key factor for mental development.