Progressive neuropsychiatric manifestations of phenylketonuria in adulthood

Neuropsychiatric signs and MRI abnormalities can occur in patients with phenylketonuria in adulthood. We describe clinical and radiological features of phenylketonuric patients and we discuss the advantage of continuing diet in adulthood.

We report late onset neuropsychiatric symptoms of four phenylketonuric patients (33-45years) diagnosed in infancy and report the case of a patient (33years) diagnosed with phenylketonuria because of late onset neurological signs. We describe clinical and radiological features of these 5 patients, and their evolution under diet and propose a review of the literature.

The main neurological abnormalities in phenylketonuric patients diagnosed in infancy are: brisk reflexes, spastic paraparesis, psychiatric signs that appear 10.5years after the diet arrest. A leukoencephalopathy was present in 93% of cases and 91.7% improve clinically after poor phenylalanine diet reintroduction. In 4 patients, neurological abnormalities (spastic paraparesis, dementia, Parkinsonism) led to the late diagnosis. Two of them had a leukoencephalopathy on brain MRI. Patients had high levels of phenylalanine (above 1500μmol/L) when neuropsychiatric signs occurred. Improvement after diet suggests that hyperphenylalaninemia has a direct toxic effect on the brain.

The long-term follow-up of phenylketonuric patients is mandatory to depict and treat neurological complications in time. Diet reintroduction is efficacious in most cases.