Classical PMD − Type I - presents with delayed motor development in the first three years of life and nystagmus (shaking of the eyes). The difficulties with movement can include spasticity (stiff or rigid muscles), hypotonia (floppiness), choreoathetosis (extra movements) and ataxia (unsteadiness/loss of coordination). Slow progress is made to sitting or sometimes walking, and speech. This is followed by slow deterioration in the second decade of life. Congenital or Type II can begin in the first few months and runs a much more severe course than Type I, which may include epilepsy and a very limited life span. There is an intermediate Type III described and what is known as PMD-like disease.
Also known as: Cockayne-Pelizaeus-Merzbacher disease
Pelizaeus-Merzbacher disease (PMD) is a neurological disorder and involves the deficiency and loss of myelin (the white matter of the brain). Children with PMD display seriously affected development. PMD was described more than 100 years ago and a number of different types have been described since.
What are the symptoms?
What are the causes?
The disorder is caused by a range of defects in PLP1 gene on chromosome Xq22 that controls proteolipid protein, an important constituent of myelin. This is not the case for PMD-like disease where different genes and inheritance are described.
How is it diagnosed?
Magnetic resonance imaging (MRI) scans can usually be used for diagnosis in the appropriate clinical setting.
Inheritance patterns and prenatal diagnosis
The main types of PMD (I,II,III) are inherited as X-linked recessive (boys only are affected and female relatives may be carriers). PMD-like disease appears to have a different genetic basis and may be autosomal recessive.
Is there support?
Information and support in the UK for metabolic diseases is provided by Climb (see entry Inherited Metabolic diseases).