[Adult onset Alexander disease with a novel variant (S398F) in the glial fibrillary acidic protein gene]

Alexander disease causing mutations in the C-terminal domain of GFAP are deleterious both to assembly and network formation with the potential to both activate caspase 3 and decrease cell viability

Alexander disease is a primary genetic disorder of astrocyte caused by dominant mutations in the astrocyte-specific intermediate filament glial fibrillary acidic protein (GFAP). While most of the disease-causing mutations described to date have been found in the conserved α-helical rod domain, some mutations are found in the C-terminal non-α-helical tail domain. Here, we compare five different mutations (N386I, S393I, S398F, S398Y and D417M14X) located in the C-terminal domain of GFAP on filament assembly properties in vitro and in transiently transfected cultured cells. All the mutations disrupted in vitro filament assembly. The mutations also affected the solubility and promoted filament aggregation of GFAP in transiently transfected MCF7, SW13 and U343MG cells. This correlated with the activation of the p38 stress-activated protein kinase and an increased association with the small heat shock protein (sHSP) chaperone, αB-crystallin. Of the mutants studied, D417M14X GFAP caused the most significant effects both upon filament assembly in vitro and in transiently transfected cells. This mutant also caused extensive filament aggregation coinciding with the sequestration of αB-crystallin and HSP27 as well as inhibition of the proteosome and activation of p38 kinase. Associated with these changes were an activation of caspase 3 and a significant decrease in astrocyte viability. We conclude that some mutations in the C-terminus of GFAP correlate with caspase 3 cleavage and the loss of cell viability, suggesting that these could be contributory factors in the development of Alexander disease.

Nationwide survey of Alexander disease in Japan and proposed new guidelines for diagnosis

Alexander disease (AxD) is a rare neurodegenerative disorder characterized by white matter degeneration and formation of cytoplasmic inclusions. Glial fibrillary acidic protein (GFAP) mutations have been reported in various forms of AxD since 2001. However, a definitive diagnosis remains difficult because of uncertain prevalence, and different clinical features seen in infantile AxD and adult AxD may lead to confusion and misdiagnosis. Here we report an epidemiological study conducted in Japan. Two nationwide questionnaire-based surveys were conducted using tentative diagnostic criteria. We gathered information regarding prevalence, neurological findings, magnetic resonance imaging (MRI) findings, electrophysiological findings, genetic information, and the results of therapeutic interventions and home care. Prevalence of various forms of AxD was determined as 27.3% (infantile), 24.2% (juvenile), and 48.5% (adult). Prevalence of AxD in Japan was estimated to be approximately 1 case per 2.7 million individuals. The main characteristics of infantile and juvenile AxD include delayed psychomotor development or mental retardation, convulsions, macrocephaly, and predominant cerebral white matter abnormalities in the frontal lobe on brain MRI. The main characteristics of adult AxD include bulbar signs, muscle weakness with hyperreflexia, and signal abnormalities and/or atrophy of medulla oblongata and cervical spinal cord on MRI. To ensure correct diagnosis of AxD, the physician should understand the importance of the process of GFAP genetic testing, which provides definitive diagnosis. Therefore, we propose new clinical guidelines for diagnosing AxD based on simplified classifications: cerebral AxD (type 1), bulbospinal AxD (type 2), and intermediate form (type 3).

Adult-onset Alexander disease with typical "tadpole" brainstem atrophy and unusual bilateral basal ganglia involvement: a case report and review of the literature

BACKGROUND

Alexander disease (ALX) is a rare neurological disorder characterized by white matter degeneration and cytoplasmic inclusions in astrocytes called Rosenthal fibers, labeled by antibodies against glial fibrillary acidic protein (GFAP). Three subtypes are distinguished according to age at onset: infantile (under age 2), juvenile (age 2 to 12) and adult (over age 12). Following the identification of heterozygous mutations in GFAP that cause this disease, cases of adult-onset ALX have been increasingly reported.

CASE PRESENTATION

We present a 60-year-old Japanese man with an unremarkable past and no family history of ALX. After head trauma in a traffic accident at the age of 46, his character changed, and dementia and dysarthria developed, but he remained independent. Spastic paresis and dysphagia were observed at age 57 and 59, respectively, and worsened progressively. Neurological examination at the age of 60 revealed dementia, pseudobulbar palsy, left-side predominant spastic tetraparesis, axial rigidity, bradykinesia and gaze-evoked nystagmus. Brain MRI showed tadpole-like atrophy of the brainstem, caused by marked atrophy of the medulla oblongata, cervical spinal cord and midbrain tegmentum, with an intact pontine base. Analysis of the GFAP gene revealed a heterozygous missense mutation, c.827G>T, p.R276L, which was already shown to be pathogenic in a case of pathologically proven hereditary adult-onset ALX.

CONCLUSION

The typical tadpole-like appearance of the brainstem is strongly suggestive of adult-onset ALX, and should lead to a genetic investigation of the GFAP gene. The unusual feature of this patient is the symmetrical involvement of the basal ganglia, which is rarely observed in the adult form of the disease. More patients must be examined to confirm, clinically and neuroradiologically, extrapyramidal involvement of the basal ganglia in adult-onset ALX.