Alexander disease is a rare disorder with limited understanding of its cause, although it does seem to be a disorder of astrocytes rather than a leukodystrophy. It can be divided into three groups: infantile, juvenile, and adult. The infantile type shows enlargement of the head, retarded development and evidence of a severe neurological disorder. The juvenile sufferers are more likely to exhibit bulbar signs, and may not be significantly retarded. Among adults the condition can fluctuate, and so mimic multiple sclerosis. The differential diagnosis in these three groups is discussed, especially the unusual ways in which they can present. The definitive diagnosis may depend on demonstrating Rosenthal fibres in a brain biopsy, or at autopsy, but other tests can be suggestive. The cerebrospinal fluid can show an elevation of B-crystallin and heat shock protein, and the GFAP gene is considered a reliable marker. The EEG and magnetic imaging findings are non-specific. Pathological studies of the brain can be characteristic with demyelination, especially in the frontal lobes, and Rosenthal fibres concentrated in the subpial and subependymal areas. It is possible that these fibres cause a dysfunction of the astrocytes. The genetic investigations are reviewed, and possible causes are discussed. These remain theoretical, but it has been suggested that the disorder is a response to stress from some unknown stimulus. Rosenthal fibres seem to be the result of the condition, although they may be related to the aetiology. There is no specific treatment.

Intermediate filaments (IFs) are abundant structures found in most eukaryotic cells, including those in the nervous system. In the CNS, the primary components of neuronal IFs are α-internexin and the neurofilament triplet proteins. In the peripheral nervous system, a fifth neuronal IF protein known as peripherin is also present. IFs in astrocytes are primarily composed of glial fibrillary acidic protein (GFAP), although vimentin is also expressed in immature astrocytes and some mature astrocytes. In this Review, we focus on the IFs of glial cells (primarily GFAP) and neurons as well as their relationship to different neurodegenerative diseases.

Expression of the GFAP gene has attracted considerable attention because its onset is a marker for astrocyte development, its upregulation is a marker for reactive gliosis, and its predominance in astrocytes provides a tool for their genetic manipulation. The literature on GFAP regulation is voluminous, as almost any perturbation of development or homeostasis in the CNS will lead to changes in its expression. In this review, we limit our discussion to mechanisms proposed to regulate GFAP synthesis through a direct interaction with its gene or mRNA. Strengths and weaknesses of the supportive experimental findings are described, and suggestions made for additional studies. This review covers 15 transcription factors, DNA and histone methylation, and microRNAs. The complexity involved in regulating the expression of this intermediate filament protein suggests that GFAP function may vary among both astrocyte subtypes and other GFAP-expressing cells, as well as during development and in response to perturbations.

Fifty years have passed since the discovery of glial fibrillary acidic protein (GFAP) by Lawrence Eng and colleagues. Now recognized as a member of the intermediate filament family of proteins, it has become a subject for study in fields as diverse as structural biology, cell biology, gene expression, basic neuroscience, clinical genetics and gene therapy. This review covers each of these areas, presenting an overview of current understanding and controversies regarding GFAP with the goal of stimulating continued study of this fascinating protein.

Alexander disease is a fatal neurodegenerative disorder resulting from missense mutations of the intermediate filament protein, GFAP. The pathological hallmark of this disease is the formation of cytoplasmic protein aggregates within astrocytes known as Rosenthal fibers. Transgenic mice engineered to over-express wild-type human GFAP develop an encephalopathy with identical aggregates, suggesting that elevated levels of GFAP in addition to mutant protein contribute to the pathogenesis of this disorder. To study further the effects of elevated GFAP and Rosenthal fibers per se, independent of mutations, we performed gene expression analysis on olfactory bulbs of transgenic mice at two different ages to follow the progression of pathology. The expression profiles reveal a stress response that includes genes involved in glutathione metabolism, peroxide detoxification and iron homeostasis. Many of these genes are regulated by the transcription factor Nfe2l2, which is also increased in expression at 3 weeks. An immune-related response occurs with activation of cytokine and cytokine receptor genes, complement components and acute phase response genes. These transcripts are further elevated with age, with additional induction of macrophage-specific markers such as Mac1 and CD68, suggesting activation of microglia. At 4 months, decreased expression of genes for microtubule-associated proteins, vesicular trafficking proteins and neurotransmitter receptors becomes apparent. Interneuron-specific transcription factors including Dlx family members and Pax6 are downregulated as well as Gad1 and Gad2, suggesting impairment of GABAergic granule cells. Together, these data implicate an initial stress response by astrocytes, which results in the activation of microglia and compromised neuronal function.