Delayed diagnosis of phenylketonuria as the cause of mental retardation in an adolescent
Villaverde, R.; Escribano, J.B.; Salmerón, P.; Tortosa, D.; Meca, J.; Fernández-Barreiro, A.
Revista de Neurologia 25(148): 1911-1916
1997
ISSN/ISBN: 0210-0010 PMID: 9528029 Document Number: 480915
The hyperphenylalaninemias (HFA) form a diverse group of recessive autosomic disorders. They are caused by defects in the hepatic system for hydroxylation of the amino acid phenylalamine to tyrosine. The estimated incidence is approximately 10 cases per 100,000 live births. Children with this metabolic disorder may present with varied neurological symptoms. Control of plasma levels, so that they are more normal as soon as possible after birth, significantly prevents mental retardation and other neuropsychological dysfunction. For this reason HFA has been included in neonatal screening. However, some patients are not detected on screening. When they are adults, these patients pose problems of diagnosis for neurologists who attend adults. We describe an adolescent with mental and linguistic retardation, in whom neonatal screening to rule out metabolic defects was normal. At the age of 15, the phenylalanine in blood and urine were found to be raised. On cerebral magnetic resonance changes typical of pheynylketonuria (PKU) were seen. The HFA should be considered as causes of cerebral dysfunction in adults, since in spite of neonatal screening, false negatives may occur. We describe a clinical case and consider different forms of hyperphenylaleninemias. Their diagnosis and treatment.