Introduction: Pelizaeus-Merzbacher's disease involves extensive demyelination of the Central Nervous System. This is due to a defect in the gene for proteolipoproteins, found on the X chromosome. It appears early as marked axial hypotonia, stridor, nystagmus and anomalous movements of the head, and later as variable pyramidal, extrapyramidal and cerebellar involvement.
Clinical case: A three year old boy, with no unusual family history, was seen for psychomotor retardation. He had marked hypotonia, absence of evidence of social contact, inspiratory stridor, nystagmus and horizontal nodding movements of the head. MR at 4 months showed absence of supratentorial and infratentorial myelinization. Analysis of the gene for proteolipoproteins showed a specific mutation on the exon 5 C227Y. At eight and a half years there was persistence of the severe axial hypotonia with minimal visual function and social contact was maintained through hearing.
Conclusions: It is possible to make an early diagnosis of Pelizaeus-Merzbacher's disease in the first weeks of life, on the typical clinical picture and MR findings of marked extensive hypomyelination, although assessment of myelination is difficult at this age. Early diagnosis is very important, since molecular analysis of the proteolipoproteins gene permits confirmation of the diagnosis, identification of heterozygotes and the establishment of prenatal diagnosis.