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  Oct 15, 2018

Fahr's syndrome (FS) / Idiopathic Basal Ganglia Calcification

Fahr's syndrome (FS) is also known as Idiopathic Basal Ganglia Calcification. It is a genetically inherited neurological condition, proposed to have both an autosomal dominant and autosomal recessive mode of inheritance. FS is rare and is characterized by the abnormal deposition of calcium in locations of the brain that are involved in the control of movement.

The calcium deposits are made primarily of calcium phosphate and calcium carbonate and are commonly found in the basal ganglia, cerebral cortex, hippocampus, thalamus, dentate nucleus, and subcortical white matter.

Patients may be initially asymptomatic. FS commonly affects young to middle aged adults in the fourth or fifth decades. However, it may occur at any point in life, including childhood or adolescence.

FS manifests with a variety of progressive clinical signs and symptoms, which range from extrapyramidal system (involuntary movement motor system) symptoms to neuropsychiatric impairments of concentration and memory to disorders such as Parkinsonism (symptoms such as impaired speech, muscle stiffness), tremors, and chorea (jerky involuntary movements).

Other symptoms that may occur include headaches, vision impairment, and dementia.

Pathophysiology and Diagnostic Criteria for FS

Heterogeneity in FS has been suggested due to three possible chromosomal loci being identified. Mutations in the genes coding for type III sodium-dependent phosphate transporter 2, platelet-derived growth factor subunit B, and beta-type platelet-derived growth factor receptor have been suggested to be implicated in the condition.

The latter two are mostly active during vessel formation in the brain in order to recruit pericytes (contractile cells that wrap around the endothelial cells of capillaries and venules).

The calcification in the brain appears to be progressive, considering the observation that older individuals tend to have more extensive lesions. Moreover, there has been documented increases in calcification in patients who are closely followed up.

The deposits are found in the walls of capillaries and small to medium-sized arteries and with a much lesser frequency in veins and venules. Depositions of other compounds such as mucopolysaccharides and elements like iron, magnesium, and zinc have also been found in these vessels in FS.

The criteria that need to be met during FS diagnosis a positive family history, onset in the 40s or 50s (can be earlier), progressive neuropsychiatric or neurological complications, typical radiographic calcifications in the areas of the brain that control movement, and the ruling out of other causes.

The other causes that need to be ruled out include normal blood biochemistry (i.e. no calcium of phosphate metabolic derangements), no infectious, traumatic, or toxic causative factors, and no other genetic conditions such as mitochondrial disorders.

Treatment and Prognosis

FS has no cure and does not have a standardized treatment regimen. Current therapies are mainly targeted towards the symptoms and complications associated with the condition. Psychotic symptoms may be managed with antipsychotics like lithium and Parkinsonian effects may be handled with levodopa.

The prognosis is quite variable and several factors may contribute. Nonetheless, the progressive neurological dysfunction may eventually become quite debilitating and ultimately result in disability and/ or death. Genetic counseling is recommended for those affected in order to inform them of the consequences and nature of the disorder, while providing guidance with regards to family planning.