Fahr disease is named after Karl Theodor Fahr, a German neurologist who first reported the disorder in 1930. It is a rare neurological condition characterized by abnormal idiopathic calcification of basal ganglia and commonly has an autosomal dominant inheritance. Abnormal calcified deposits (composed of calcium carbonate and phosphate) are not just limited to basal ganglia but also occur in some other locations, such as thalamus, hippocampus, dentate nucleus, cerebral cortex, and cerebellar subcortical white matter.
Usually, in the literature, the term Fahr disease and syndrome are used interchangeably, but it has been argued that:
Fahr disease is also termed bilateral strio-pallido-dentate calcinosis or primary familial brain calcification (PFBC) or calcinosis nucleorum.
Fahr disease is most commonly found to be inherited in an autosomal dominant pattern with incomplete and age-related penetrance, but it may also be transmitted as an autosomal recessive trait or occur sporadically. Some studies have reported the phenomenon of anticipation in this disease.
There are four genes which have been implicated as the molecular basis of Fahr disease i.e., loss of function mutation in the gene SLC20A2 encoding type 3 sodium-dependent phosphate transporter 2 (PiT2) on chromosome 8p (40%), a mutation in gene XPR1 that encodes for a retroviral receptor with phosphate export function on chromosome 1q (2%), a mutation in the gene which encodes the receptor for members of the platelet-derived growth factor family- gene PDGFRB on chromosome 5q (2%), and gene PDGFB on chromosome 22q (11%). 46% of cases have some unknown gene mutations. Other loci that have been linked to Fahr disease include IBGC1 locus at chromosome 14q, a locus at chromosome 2q, and another one at chromosome 8.
Since, some genes have been implicated in Fahr disease, the term idiopathic basal ganglia calcification, used previously, should be avoided.
Fahr disease is reported to commonly affect people in their 40s and 50s. Patients are usually in good health in their youth and tend to develop this progressive neurodegenerative disease later in adulthood. The prevalence of this disease is more or less unknown due to insufficient investigations of first-degree relatives of the patients.
Abnormal calcium deposition is hypothesized to be due to either abnormal brain calcium metabolism or metastatic deposition due to locally altered blood-brain barrier. Defective iron transport and free radical production cause tissue damage, which initiates calcification around a nidus composed of mucopolysaccharides and related substances. The calcium deposition starts within the vessel wall and perivascular space and slowly extends to involve the entire neuron. Progressive calcification compresses nearby vessels reducing blood flow and hence continuing the vicious cycle of decreased blood flow, tissue injury, and mineral deposition.
High levels of copper, zinc, magnesium, iron, and altered glucose metabolism in basal ganglia have also been reported. An increase in CSF levels of CNS-specific peptide, homocarnosine, and low histidine levels have been found in some cases.
On gross pathologic examination, granular deposits and solid nodules deposited in the involved area and mild cortical atrophy are seen.
On histological examination, concentric calcium deposited along the walls of small ad medium-sized arteries is seen with less common involvement of veins. Sometimes, droplet calcifications can be observed. Ischemic changes and diffuse gliosis can be observed in the surroundings of large deposits.
On electron microscopy, calcium appears as amorphous or crystalline material surrounded by a basal membrane. In the cytoplasm of neuronal and glial cells, calcium granules can be seen.
(A) Movement disorder like features:
(B) Neuropsychiatric features 
In a study done by Batla et al., a clinical correlation with genomic abnormalities (genotype-phenotype relationship) was established after reviewing 137 cases. Those with SLC20A2 mutations were more commonly observed to have parkinsonism and involvement of the thalamus and dentate nucleus. Those with PDGFB mutations were observed to have a headache more commonly and cysts in white matter.
To meet the diagnostic criteria, the following investigations are usually done to exclude other causes of brain calcifications.
Laboratory Investigations: Routine lab results are within normal limits in a patient with Fahr disease. Any abnormality should prompt further investigations to rule out secondary causes of brain calcifications.
Imaging studies: Bilateral basal ganglia calcification is visualized in both Fahr disease and secondary causes.
Molecular Genetic Testing:
This is done in an index case that meets the diagnostic criteria to establish the diagnosis of Fahr disease. There are three approaches to genomic testing:
To this date, no definitive cure is available for Fahr disease, as with other neurodegenerative disorders, and management is focused primarily on symptomatic relief.
(A) Symptomatic Management
The use of carbamazepine, benzipenes, and barbiturates in patients with Fahr disease can lead to increased gait dysfunction. Psychiatrists and neurologists should implement great caution with the use of anti-depressants and anxiolytics as the threshold for side effects with these drugs is low in patients with Fahr disease. Lithium has been known to increase seizure risk in the patients, and neuroleptics can exacerbate extrapyramidal symptoms.
(C) Physical Rehabilitation 
(D) Genetic Counseling
The disease is transmitted in an autosomal dominant fashion. The family history is not fully conclusive. Sometimes the family history of a patient is negative because of the early death of a parent before the disease became evident, or it may have a late-onset in the parent or reduced penetrance.
There are no demonstrated medical benefits for screening the relatives. Predictive testing in the form of brain CT scan (calcium deposits precede clinical manifestations by years) and molecular testing (if PDGFB, PDGFRB, XPR1, SLC20A2 pathogenic variant has been identified in proband) can be offered to asymptomatic first-degree relatives (>18 years) after weighing the ethical and psychosocial conditions because no curative treatment is available. Testing individuals >18 years can help them in decision making in regards to their marriage, family planning, career, and finance. Testing is usually not recommended in individuals <18 years considering social issues, discrimination and anxiety in future, negative impact on parent-child or sibling-child relationship, and uncertain CT scan predictability as penetrance is age-dependent.
(E) Prenatal Counseling
Prenatal testing and preimplantation genetic diagnosis are possible for high-risk pregnancy in which PDGFB, PDGFRB, XPR1, SLC20A2 pathogenic variant has been detected in the proband.
(F) Surveillance: Annual neurologic and neuropsychiatric assessment.
Basal ganglia calcifications occur in several other familial and non-familial conditions that are required to be excluded before making a diagnosis of primary familial basal ganglia calcification.
1. Endocrine Disorders
Parathyroid hormone (PTH) disturbances are the most common cause of bilateral basal ganglia calcifications. Reduced levels of actions of PTH cause hyperphosphatemia and hypocalcemia, which promotes calcification. In a review of 150 cases of Fahr syndrome, 35 (23.3%) had idiopathic hypoparathyroidism, and 23 (15.3%) had secondary (post-thyroidectomy) hypoparathyroidism.
Hypoparathyroidism: Idiopathic (absence, fatty replacement or atrophy of parathyroid gland) or secondary (due to inadvertent removal during thyroidectomy)
Pseudohypoparathyroidism (PHP) and Pseudo-pseudohypoparathyroidism (PPHP): Both are phenotypic variants with autosomal dominant inheritance with mutation of the GNAS gene. Both have clinical features of Albright hereditary osteodystrophy. In PHP, there is resistance to the action of parathyroid hormone with hypocalcemia, hyperphosphatemia, and elevated PTH levels, but PPHP has no biochemical abnormality with normal calcium and phosphorus levels and a normal response to PTH secretion.
Kenny Caffey syndrome type 1
It is a rare skeletal disorder with a mutation in the TBCE gene and is characterized by dwarfism, cortical thickening and medullary stenosis of long bones, facial dysmorphism, hypocalcemia due to congenital hypoparathyroidism and basal ganglia calcifications.
2. Mitochondrial Myopathy
Basal ganglia calcification is a recognized finding in mitochondriopathy due to abnormal calcium homeostasis. In a study, neuro-radiological findings were studied in six kindreds of 24 subjects with MELAS; bilateral basal ganglia calcification was the commonest radiological finding.
3. Infectious Diseases
Intrauterine and perinatal infections: Herpes, CMV, rubella, and toxoplasmosis may cause basal ganglia and intracerebral calcification in the newborn and may present with microcephaly, seizures, chorioretinitis, or other CNS features.
Brucellosis: A study by Mousa AM et al. showed 9 (13.8%) out of 65 cases of CNS brucellosis (neuropsychiatric manifestations) had radiologic evidence of basal ganglia calcifications. Three cases had unilateral, 4 cases had bilaterally symmetric, and 2 cases had bilaterally asymmetric calcifications.
Toxoplasmosis: The most commonly affected region (75% cases) is basal ganglia showing multiple ring-enhancing lesions with edema and sometimes calcifications.
Neurocysticercosis: Larval cyst may sometimes occur in basal ganglia and gets calcified.
HIV/AIDS: In a study done for reporting neuropathology in 52 HIV patients, three were found to have basal ganglia calcifications.
4. Congenital Disorders
Cockayne syndrome (CS)/Neill-Dingwall Syndrome 
It is an autosomal recessive disorder with an underlying defect in DNA repair. CS type 1 is the classic variant in which there is normal development initially, and features develop after first two years of life, such as hearing and visual impairment, CNS and PNS degradation with bilateral basal ganglia calcifications. CS type 2 is a more severe congenital variant, also known as cerebro-oculofacial syndrome or Pena Shokeir type 2 syndrome. There is no postnatal neurological development with associated eye and skeletal anomalies.
It is a neurodevelopmental disorder characterized by microcephaly, neonatal seizures, cerebral atrophy, encephalopathy, cerebral calcifications typically bilateral, and in basal ganglia, especially putamen and globus pallidus.
Tuberous Sclerosis Complex
It is an autosomal dominant neurocutaneous syndrome with a mutation in TSC1 and TSC2 genes. It exhibits features involving the skin (ash-leaf macules, shagreen patch, adenoma sebacum, angiofibroma), kidneys (angiomyolipoma), cardiac (rhabdomyosarcoma) and CNS (subependymal nodules, hamartomas, cortical and subcortical tubers which can get calcified). The frequency of calcifications increases with age.
Coats plus syndrome (CRMCC-Cerebroretinal microangiopathy with calcifications and cysts)
Coats disease is a congenital nonhereditary eye disorder characterized by abnormal development of blood vessels behind the retina with resultant complete or partial blindness. Coats plus disease has associated neurologic features with intracerebral calcifications and formation of parenchymal cysts, bone, and gastrointestinal abnormalities.
Down Syndrome: In a study by Takashima et al. in 33 patients of down syndrome, 45% had basal ganglia calcifications, especially located in globus pallidus, and it increased with age.
Others: Immunodeficiency 38 with basal ganglia calcification, PKAN (Pantothenate kinase-associated neurodegeneration)
5. Adult-Onset Disorders
Neuroferritinopathy: Autosomal dominant disease, a variant of NBIA (neurodegeneration with brain iron accumulation), which presents with adult-onset dystonia, cognitive and behavioral changes with radiographic evidence of excessive iron storage and cystic degeneration of putamen.
Spinocerebellar ataxia type 20: Autosomal dominant disease with marked calcifications in the cerebellum (especially dentate nucleus).
Polycystic lipomembranous osteodysplasia with sclerosing leukoencephalopathy (PLOSL, Nasu-hakola disease): Autosomal recessive disease which presents with fractures, dementia, and bilateral basal ganglia (esp putamen) calcifications.
Others: DNTC-Diffuse neurofibrillary tangles with calcification (Kosaka- Shibayama disease), DRPLA- Dentatorubral-pallidoluysian atrophy (Haw river syndrome).
6. Dermatological Conditions
Lipoid proteinosis: It is a rare genodermatosis in which amorphous hyaline material accumulates intracellularly in the skin, mucous membranes, and internal organs. Manifestations include alopecia, photosensitivity, dwarfism, seizures, and dementia. Selective brain parenchymal calcifications occur in the amygdala, corpus striatum, hippocampus, and parahippocampal gyrus.
Dyskeratosis Congenita: It is a disorder with a classic triad of dysplastic nails, lacy reticular pigmentation of the upper chest, and oral leukoplakia. Intracranial calcifications have been reported in the Revesz syndrome variant.
Neural necrosis has been reported with excess vitamin D, lead, mercury, ionizing radiation, and methotrexate therapy.
8. Normal Aging
0.3-1.5 % of brain CT scans are incidentally found to have basal ganglia calcifications. In a study done by Forstl et al., about 70% of autopsies had microscopic calcifications in globus pallidus and the dentate nucleus, but patients were usually asymptomatic. In a study done by Ostling et al., basal ganglia calcification was strongly correlated with psychotic symptoms in the elderly.
Some other reported conditions with brain calcifications include biotinidase deficiency, hereditary folate malabsorption, carbonic anhydrase deficiency, celiac disease, cerebral lupus, and tetrahydrobiopterin-deficient hyperphenylalaninemia.
The prognosis of a patient with Fahr disease is variable and unpredictable. There is no correlation between the age of disease onset, symptoms at onset, or extent of calcifications in the brain with the severity of the disease. Penetrance is age-dependent, with a 95% occurrence by the age 50. As such, an asymptomatic disease carrier might present with a negative CT scan at a younger age. Calcifications have been reported to become more extensive with age, as evidenced by follow up scans of confirmed cases.
Although Fahr disease is a rare disorder it has some crippling complications. Following are some of the complications that the providers should be aware of:
Following are some advisable consultations in order to ensure the best outcomes in patients suffering from Fahr disease:
Diagnosis with a chronic and progressive neurological disease can be a frightening experience for many patients. Patient education plays a pivotal role in long term management and follow up of Fahr disease due to its incurable and progressive nature.
A patient might experience a wide range of emotions, such as fear, anger, depression, anxiety after the diagnosis. Talking to other people suffering from other neurodegenerative diseases may help them to share experiences and information.
Physical and Exercise Therapy
Exercise can help patients feel better physically and mentally. It helps to improve balance, flexibility, strength, prevent the development of contractures, quality of life, and socialization. Strengthening and stretching exercises should be advised. Studies have shown that aerobic exercises like walking, riding a stationary bicycle, water aerobics, etc. in patients with parkinsonism features are energizing.
Patients and caretakers are encouraged to make home safe as much as possible by:
As long as no motor symptoms are there, patients can drive, but driving ability should be re-evaluated from time to time, especially if the motor or cognitive decline is observed. If patients start developing seizures, patients are encouraged to discontinue driving. Advise them to use other means of transportation like walking, cabs, public buses, trains.
Fahr disease is a rare disease that has no cure, as such, interprofessional team management is the best way to manage this disease. The key providers include physicians, nurses, pharmacists, social workers, and physical therapists.
Nurses can educate the patient and family and increase their participation in decision making. They might be the first one to catch any changes in daily living with worsening or new onset of symptoms and assessing the fall risk, hence can make appropriate referrals and recommendations.
Most patients are elderly and receive symptomatic care in the absence of curative drugs and hence likely be on polypharmacy. Pharmacists play a huge role in assessing drug interactions, safety profiles, and adverse events.
Social workers can help provide psycho-social support and refer the patients to nursing homes. End of life care, financial planning, disability application information should also be provided to the patients by nurses and social workers. [Level 5]
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