Pelizaeus Merzbacher’s disease (PMD) is a hereditary disorder of central myelinization caused by mutations of the proteolipid protein (PLP) gene situated on the X chromosome. Clinically PMD is characterized by typical symptoms with early nystagmus, late psychomotor development of varying grades – depending on the type of PMD, spasticity with hyperreflexia and pyramidal phenomena, cerebellar symptomatology, markedly prolonged latencies of auditory and optically evoked potentials and typical hyperintense findings in the white matter of the brain on MRI. According to the severity of the affection usually the more frequent and milder so-called classical form is differentiated from the rarer and more severe, so-called connatal form.The PLP gene can be damaged by two types of mutations – more frequently (60–70%) duplication of the whole gene which leads to the classical form of PMD and the less frequent (20–30%) various point mutations which lead to a spectrum of clinical phenotypes from connatal to very mild forms of spastic paraplegia type 2 (SPG2). The authors describe the clinical findings and results of examination in the first group od four Czech patients with the classical form of PMD where after assessment of the clinical diagnosis its correctness was subsequently confirmed by evidence of duplication of thePLPgene. In two boys originally incorrectly the diagnosis of the hypotonic form of infantile cerebral palsy was made and in two the authors established the diagnosis of PMD and explained the psychomotor retardation of the patients. The signalling symptoms in all four boys were early nystagmus, hypotonia and retarded motor development. Duplication of the PLP gene was proved by quantitative comparative PCR with fluorescent labelling (QCFPCR) and by means of an intragenic microsatellite marker. In all instances carrier of duplication of the PLP gene – was also the patient’s mother although in three instances a clinically and anamnestically sporadic affection was involed and only in one family a familial, multiple incidence of PMD in the family was recorded. Findings from a typical phenotype of these patients with molecular genetically confirmed diagnosis should lead to an easier, more direct and earlier assessment of the correct diagnosis also in other patients with PMD in our country, incl. adult patients.

        Key words: Pelizaeus Merzbacher disease, proteolipid protein gene, dysmyelinization