Basal Ganglia Calcification, Idiopathic, 5

A number sign (#) is used with this entry because idiopathic basal ganglia calcification-5 (IBGC5) is caused by heterozygous mutation in the PDGFB gene (190040) on chromosome 22q13.

Description

Idiopathic basal ganglia calcification-5 (IBGC5) is an autosomal dominant disorder characterized by progressive neurologic symptoms that are associated with brain calcifications mainly affecting the basal ganglia. Calcifications may also occur in the thalamus, cerebellum, or white matter. Affected individuals have motor symptoms, such as dyskinesias or parkinsonism, headache, cognitive impairment, and psychiatric manifestations, including apathy and depression. Some patients are asymptomatic. The age at symptom onset ranges from late childhood to adulthood; the disorder is progressive (summary by Keller et al., 2013).

For a detailed phenotypic description and a discussion of genetic heterogeneity of IBGC, see IBGC1 (213600).

Clinical Features

Kostic et al. (2011) reported a 4-generation Serbian family in which 6 individuals had symmetric brain calcifications ascertained by CT scan. Two individuals with brain calcifications were asymptomatic. The 4 other individuals developed neurologic symptoms between ages 22 and 55.4 years. The main clinical findings included parkinsonism, severe gait disturbances with freezing of gait, dyskinesia, and psychiatric manifestations. Brain perfusion single photon emission CT showed predominant hypoperfusion in the frontal cortex and the basal ganglia.

Keller et al. (2013) reported 6 unrelated families with IBGC, including the Serbian family described by Kostic et al. (2011). The mean age at symptom onset was 23.9 years (range 10 to 55 years), although at least 5 individuals with calcifications were asymptomatic, the oldest being 57 years of age. Twelve patients had motor signs, including dystonia/dyskinesias in 8, parkinsonism in 3, and chorea in 3, and 9 patients had cognitive impairment or psychiatric disease, such as psychosis, apathy, and depression. The most common symptom was migraine or headache, present in 13 patients. Brain imaging in all 31 mutation carriers showed calcification in the basal ganglia. Some patients also had calcification in other brain regions, including the thalamus, cerebellum, and cerebral and subcortical white matter.

Inheritance

The transmission pattern of IBGC5 in the families reported by Keller et al. (2013) was consistent with autosomal dominant inheritance.

Molecular Genetics

Keller et al. (2013) identified 6 different heterozygous putative loss-of-function mutations in the PDGFB gene (see, e.g., 190040.0003-190040.0007) in 6 (18.8%) of 13 families with idiopathic basal ganglia calcification-5. The initial mutations were found by genome or exome sequencing.

Animal Model

Keller et al. (2013) found that 4-month-old mice homozygous for a hypomorphic Pdgfb allele developed clusters of calcified nodules in the midbrain and thalamus. At age 1 year, mutant mice had more extensive calcification involving the basal forebrain, midbrain, and pons. The lesions were punctate and composed of calcium phosphate. Transgenic reexpression of 2 copies of wildtype endothelial Pdgfb in Pdgfb-null mice prevented the development of brain calcification, whereas reexpression of 1 copy of the rescue allele did not prevent calcification. The findings suggested that it is endothelial Pdgfb, rather than neuronal Pdgfb, that drives the pathology. Keller et al. (2013) postulated that the brain calcification may result from defects in pericytes and the blood-brain barrier.