Alexander's disease (AxD), described by Stewart Alexander in 1949, is a fatal, albeit rare, disease that strikes infants and young adults; AxD is the only example of a primary disease of astrocytes, which is associated with their intrinsic malfunction. The histological hallmark of AxD is the presence of Rosenthal fibres in astrocytes, which are cytoplasmic inclusions, formed by GFAP in association with stress proteins (such as a- and P-crystallin and heat shock protein 27). Infantile and juvenile AxD is mostly caused by mis-sense mutations of the GFAP gene; these aberrant genes are absent in parents, and therefore represent de-novo dominant GFAP gene mutations. Very rarely, AxD can be diagnosed in adults, but the aetiology remains unclear. Infantile AxD usually becomes manifest around six months of age and the symptoms include head enlargement, convulsions, pyramidal symptoms, and muscle weakness. The infants die within two to four years after the onset of the disease. The juvenile form (onset ~nine years, average survival eight years after diagnosis) is characterized by progressive paresis. The precise nature of AxD pathology is not defined, but the progression of the disease is determined by rapidly developing demyelination. There are suggestions that AxD development may result from permanent disruption of the blood brain barrier (as Rosenthal fibres tend to accumulate in endfeet, both in perivascular and pial zones), and overall malfunction of astrocytes.
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