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Requests for reprints should be addressed to Yi Guo, Department of Neurosurgery, Peking Union Medical College Hospital, Chinese Academy of Medical Sciences and Peking Union Medical College, 1 Shuaifuyuan, Dongcheng District, Beijing, 100730, China.
A 57-year-old man presented to the Neurology Clinic with a 6-year history of progressive bilateral static tremor, bradykinesia, and gait initiation difficulty. His non-motor manifestations included constipation and pollakiuria. Initial levodopa test revealed excellent responsiveness, with Unified Parkinson's Disease Rating Scale scores improving from 57 to 14 points (75%). No signs of atrophy in the cerebrum, cerebellum, or brain stem were found on the magnetic resonance imaging. Parkinson's disease was clinically diagnosed. Computerized tomography of the head showed bilateral, symmetric, dense calcifications in the basal ganglia and cerebellum (FigureA). His serum calcium level was normal, and he had normal parathyroid functions. Whole exome sequencing was then performed, and a heterozygous variant in the SLC20A2 gene, c.1784C>T (p.Thr595Met), was suspected as the disease-causing gene mutation. Therefore, the combination of bilateral brain calcifications, normal phosphate-calcium metabolic function, and SLC20A2 gene mutation contributed to the final diagnosis of idiopathic basal ganglia calcifications (iBGC), or Fahr's disease.
Compared with secondary BGC that are caused mainly by endocrine abnormalities, cerebrum infections, or toxic exposures,
The SLC20A2 gene on chromosome 8 encodes a sodium-dependent phosphate transporter, protein PiT-2, which is highly active in the neurons in the brain. SLC20A2 gene mutations cause impaired transport of inorganic phosphate across the cells and the subsequent calcium phosphate deposition mostly in deep brain structures, such as basal ganglia and thalamus, leading to neuronal degeneration and gliosis and thus resulting in movement disorders. Parkinson's disease is one of the most common movement disorders in the course of iBGC.
However, research on its application in alleviating iBGC-related movement disorders is still lacking. Because the patient developed severe on-off episodes and dyskinesias despite optimal medical treatment, he was recommended for and accepted DBS surgery. The intracranial electrodes targeting the bilateral subthalamic nucleus were successfully positioned with the help of the carefully-designed trajectory plans avoiding being influenced by the dense calcifications (Figure B). At follow-up, 8 weeks after surgery, his dyskinesias and on-off complications as well as the Unified Parkinson's Disease Rating Scale scores significantly improved. The frequency and dose of the dopaminergic medication were also reduced compared with the preoperative level.
Basal ganglia calcifications (Fahr's syndrome): related conditions and clinical features.