Alexander disease (AxD) is a rare, typically progressive neurodegenerative disorder classified as a leukodystrophy because it primarily affects white matter in the brain. It is caused by dominant, gain-of-function mutations in the GFAP (Glial Fibrillary Acidic Protein) gene. These mutations lead to accumulation of Rosenthal fibers — cytoplasmic inclusions composed of mutant GFAP protein bundled with stress proteins — in astrocytes throughout the central nervous system. [1][2]
The disease derives its name from Dr. Wilhelm Alexander, who first described Rosenthal fibers in 1949. The genetic basis was identified in 2001, distinguishing it from other leukodystrophies. [3]
Alexander disease presents in three main clinical forms, determined largely by mutation type and age of onset: [4][2:1]
| Form | Onset Age | Prevalence | Key Features |
|---|---|---|---|
| Infantile | Birth to 2 years | ~70% of cases | Megalencephaly, seizures, developmental regression |
| Juvenile | 2 to 12 years | ~20% of cases | Ataxia, spasticity, cognitive decline |
| Adult | >12 years to elderly | ~10% of cases | Bulbar symptoms, sleep disturbance, milder course |
The infantile form has the most severe phenotype, with rapid progression and median survival of 5-10 years. Adult-onset forms can be slowly progressive and are often misdiagnosed as multiple sclerosis or other neurological conditions. [3:1]
The GFAP gene on chromosome 17q21 encodes a 432-amino-acid intermediate filament protein that is the primary cytoskeletal component of astrocytes. As a type III intermediate filament, GFAP shares structural features with desmin, vimentin, and peripherin. Under normal conditions, GFAP polymerizes into filaments that provide structural support and participate in astrocyte function including astrocyte-neuron metabolic coupling and glutamate homeostasis. [1:1][3:2]
Over 150 pathogenic GFAP mutations have been identified, almost exclusively as heterozygous de novo variants. The mutations are predominantly missense substitutions affecting conserved residues. Key mutation features:
| Region | Common Mutations | Phenotype |
|---|---|---|
| Exon 1 | R79C, R79H, R88C | Predominantly infantile |
| Exon 2 | L115P, E119Q | Variable |
| Exon 4 | R239C, R239H, G244S | Variable/juvenile |
| Exon 5 | R320C, R320H | Juvenile |
| Exon 6 | D416N, K420E, L422P | Adult |
| Exon 8 | c.806+1G>A splice | Adult |
The position of the mutation within GFAP correlates with clinical phenotype: [4:1][2:2]
GFAP mutations cause Alexander disease through several interconnected mechanisms: [3:3][2:3]
MRI findings are characteristic and correlate with clinical subtype: [5]
Alexander disease: a novel mutation in the extreme carboxyl-terminus of glial fibrillary acidic protein. Journal of Neurology Neurosurgery and Psychiatry. 2004. ↩︎ ↩︎
Alexander disease: a review and updated consensus statement. Neurology. 2023. ↩︎ ↩︎ ↩︎ ↩︎
Mutations in GFAP gene cause Alexander disease: a review of clinical and genetic aspects. International Journal of Molecular Sciences. 2021. ↩︎ ↩︎ ↩︎ ↩︎
GFAP mutations, age at onset, and temporal patterns of astroglial dysfunction in Alexander disease. Annals of Neurology. 2011. ↩︎ ↩︎
MRI findings in Alexander disease. American Journal of Neuroradiology. 2022. ↩︎
Therapeutic advances in Alexander disease. Neuropediatrics. 2019. ↩︎