Comparative neuroimaging with pathologic correlates in Alexander's disease

Asymptomatic hereditary Alexander's disease caused by a novel mutation in GFAP

We report on a family with dominantly inherited asymptomatic Alexander's disease due to a novel Glial fibrillary acidic protein (GFAP) mutation. The proband, a 16-month-old boy, presented with megalocephaly and brain magnetic resonance imaging (MRI) showing the typical findings of Alexander's disease. Molecular analysis showed that he was a heterozygote of the L331P mutation of GFAP. His mother and sister, without megalocephaly or other neurological abnormalities, were also heterozygotes of the mutation and their brain magnetic resonance imaging showed mild changes in the caudates and deep frontal white matters. These results suggest the existence of a forme fruste of Alexander's disease. The L331P mutation may be associated with the mild phenotype of Alexander's disease. To elucidate the genotype-phenotype correlation in Alexander's disease, molecular diagnosis and MRI examination are required for many patients and their families.

Alexander disease

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.

Alexander disease: new insights from genetics

Prior to finding that GFAP mutations underlie many cases of Alexander disease, it was unclear whether the disease originated in astrocytes or if the formation of Rosenthal fibers was a response to an external insult. It was also unclear whether the etiology of the disease was environmental or genetic. For many cases of Alexander disease, these questions have now been answered. An immediate clinical benefit of this discovery is the possibility of diagnosing most cases of Alexander disease through analysis of patient DNA samples, rather than resorting to brain biopsy. In addition, fetal testing is now an option for parents who have had an Alexander disease child with an identified mutation and who wish to have additional children. For the future, these mutations should provide a unique window for illuminating the mechanism of the disease.

Alexander's disease: unique presentation

Subacute necrotizing encephalomyelopathy (Leigh syndrome) refers to a nebulous disease entity characterized by lactic acidosis, a wide variety a clinical manifestations, and a consistent conglomeration of pathologic findings. Several abnormalities in metabolism have been delineated in association with Leigh syndrome, but many cases have no identified metabolic abnormality. We report a case that clinically, metabolically, and neuroradiologically appeared to be Leigh syndrome. In addition, our patient exhibited other unusual clinical findings, including ocular motility abnormalities. Neuropathologically, however, the diagnosis of Alexander's disease was confirmed. A review of the literature failed to find other cases of Alexander's disease reported with the metabolic abnormalities and clinical manifestations with which our patient presented.

A case of macrocephaly, hydrocephalus, megacerebellum, white matter abnormalities and Rosenthal fibres

The authors report the case of a young boy with macrocephaly, cerebellar symptoms and signs of raised intracranial pressure. Magnetic resonance imaging showed obstruction of the aqueduct, ventricular enlargement of the cerebellum and areas of increased signal intensity in the cerebellar and frontal white matter. A stereotactic biopsy of the cerebellum showed many Rosenthal fibres and glial proliferation. Although the histopathological and neuroradiological findings were suggestive of Alexander's disease, the initial presentation and clinical course were unusual for this diagnosis. The authors suggest that a separate form of Alexander's disease should be distinguished with predominant clinical, neuroradiological and neuropathological cerebellar involvement. This form also seems to have a better life-expectancy.

Alexander's disease: clues to diagnosis

The clinical, radiologic, neurophysiologic, and pathologic findings in 10 children with histologically proven Alexander's disease are described, and the presence of two broad clinical subgroups is confirmed. Macrocephaly, regression, and seizures are found in the infantile form, whereas bulbar signs predominate the so-called juvenile form. None of the clinical or neurophysiologic findings is pathognomonic, and radiologic features suggesting the diagnosis are not present in all cases. However, the combination of abnormalities may suggest the diagnosis and justify histologic confirmation.

Two possible cases of Alexander disease. Multimodal evoked potentials and MRI

We describe two unrelated girls with slowly progressive leukodystrophy with macrocephaly. On MRI, both patients exhibited diffuse involvement of the cerebral white matter, excluding the internal capsule and optic radiation. Their visual-evoked potentials were normal. Short-latency somatosensory-evoked potentials exhibited the absence of early scalp components. Auditory brainstem responses in both patients showed intramedullary conduction disturbance. These MRI and electrophysiological findings are similar to those in infantile Alexander disease.