2q37 as a susceptibility locus for idiopathic basal ganglia calcification (IBGC) in a large South Tyrolean family

Basal ganglia calcification: 'Fahr's disease'

Brain calcification is often detected incidentally, but basal ganglia calcification has a wide differential diagnosis, including genetic and acquired causes. Primary familial brain calcification (PFBC) (formerly 'Fahr's disease') refers to neurological disorders characterised by bilateral, symmetrical deposition of calcium-hydroxyapatite crystals in the basal ganglia and other encephalic regions, with a presumed genetic basis. Its clinical picture encompasses motor, cognitive and psychiatric manifestations in various combinations. Seven genes have been linked to PFBC since 2012, with either autosomal dominant (SLC20A2, PDGFRB, PDGFB and XPR1) or recessive (MYORG, JAM2 and NAA60) mode of inheritance. Mendelian gene discovery has provided critical insights into the pathogenesis of PFBC. Dyshomeostasis of inorganic phosphate, impaired endothelial functions and disrupted blood-brain barrier integrity has been identified as converging pathomechanisms, which could highlight the targets of potential disease-modifying treatments. We provide a state-of-the-art overview on phenotypic features, diagnosis, aetiopathogenesis and management of PFBC.

Unveiling distinct clinical manifestations of primary familial brain calcifications in Asian and European patients: A study based on 10-year individual-level data

BACKGROUND

Primary Familial Brain Calcification (PFBC) can manifest clinically with a complex and heterogeneous array of symptoms, including parkinsonism, dysarthria, and cognitive impairment. However, the distinct presentations of PFBC in Asian and European populations remain unclear.

METHODS

We conducted a systematic search of PubMed for studies involving genetically confirmed PFBC patients. Demographic data, genetic information, radiological examinations, and clinical characteristics were extracted for each case.

RESULTS

The study included 120 publications and 564 genetically confirmed PFBC patients. Asian and European PFBC populations represented 54 % and 37 % of global patients, respectively. While calcification patterns showed no significant differences between Asian and European PFBC patients, European autosomal dominant PFBC variant carriers were more likely to exhibit clinical symptoms compared to their Asian counterparts (OR = 2.90, 95 % CI 1.55-5.60) and had an earlier estimated age of onset (median age 42 vs 58).

CONCLUSION

The interaction between regional differences and genetically determined calcification severity may collectively influence PFBC symptom progression. Future research should further explore the potential roles of gene modifiers, ethnic background, socioeconomic and environmental exposure factors underlying regional differences in PFBC progression.

Fahr's Disease: Case Presentation With Facial Numbness

Fahr's disease is a rare hereditary neurological disorder characterized by idiopathic basal ganglia and cerebral cortex calcifications. It presents a wide range of neurological manifestations, including motor dysfunction, sensory deficits, seizures, headaches, visual disturbances, and movement disorders. We present a case report of a 42-year-old female who presented to the accident and emergency department with a stroke alert. Her main symptom was left facial numbness. Otherwise, she was fit and well. A CT scan of her head revealed significant bilateral basal ganglia calcifications rather than ischaemic or haemorrhagic changes. Blood tests showed normal serum calcium, normal phosphate, and normal parathyroid hormone levels. Upon further inquiry, she mentioned that her sister had been diagnosed with similar findings on a brain scan. Subsequently, an MRI scan of her brain was performed, which suggested Fahr's disease. Currently, there is no definitive management available, so a conservative management approach is usually employed based on symptomatology. This case is particularly interesting due to its rarity, strong genetic inheritance, and the development of a management plan.

Coexistent meningioma in a patient with primary familial brain calcification: A case report

Primary familial brain calcification (PFBC) is an idiopathic pathology characterized by the development of calcific deposits in the supratentorial region such as telencephalon and diencephalon but also, in more extensive forms, in the cerebellum. Meningiomas are among the most common central nervous system (CNS) tumors generally related to a good prognosis. The simultaneous presence of intracerebral or extra-axial tumors and PFBC represents an exceedingly rare occurrence. A 72-year-old female patient was admitted to our department because of anoculogyric crisis followed by generalized seizures. She performed a brain CT scan which showed widespread hyperdensities in the paraventricular supratentorial region, basal ganglia and at the level of bilateral cerebellar dentate nuclei, characteristics of PFBC. Concomitant left frontal and smaller right temporal extra-axial lesions were identified and then confirmed in a brain MRI. The patient underwent a microsurgical resection of the lesion and subsequent histological examination reported a meningothelial meningioma (WHO Grade I). According to our literature review, this is the first paper that reports the coexistence of both intracranial meningiomas and PFBC. To date, it is not possible to provide an exact correlation between pathogenesis and genetic mechanism underlying this association.

Idiopathic basal ganglia calcification associated with new MYORG mutation site: A case report

BACKGROUND

Idiopathic basal ganglia calcification (IBGC) is a neurodegenerative disease characterized by symmetrical calcification of basal ganglia and other brain region, also known as Fahr’s disease. It can be sporadic or familial, and there is no definite etiology at present. With the development of neuroimaging, the number of reports of IBGC has increased in recent years. However, due to its hidden onset, diverse clinical manifestations, and low incidence, it is likely to be misdiagnosed or ignored by potential patients and their family.

CASE SUMMARY

We report a case of a 61-year-old man who presented with symptoms of dysphagia and alalia. His computed tomography scan of the brain revealed bilateral symmetric calcifications of basal ganglia, cerebellum, thalamus, and periventricular area. The genetic test showed a new mutation sites of MYORG, c.1438T>G mutation and c.1271_1272 TGGTGCGC insertion mutation. He was finally diagnosed with IBGC.

CONCLUSION

It is important to detect MYORG mutation when IBGC is suspected, especially in those without an obvious family history, for better understanding of the underlying mechanism and identifying potential treatments.

Primary familial brain calcifications: genetic and clinical update

PURPOSE OF REVIEW

In the last 7 years, changes in five genes [SLC20A2, PDGFRB, PDGFB, XPR1, and MYORG] have been implicated in the pathogenesis of primary familial brain calcification (PFBC), allowing for genetic delineation of this phenotypically complex neurodegenerative disorder. This review explores how the ensuing plethora of reported PFBC patients and their disease-causing variants improved our understanding of disease, pathogenesis, clinical manifestation, and penetrance.

RECENT FINDINGS

In PFBC patients, pathogenic changes have been most frequently described in SLC20A2, accounting for approximately the same number of patients as the variants in the other four PFBC genes combined. There is no appreciable relationship between any combination of the following three variables: the type of disease-causing change, the pattern or extent of calcifications, and the presence or nature of clinical manifestation in PFBC patients. Nevertheless, elucidation of underlying genetic factors provided important recent insights into the pathogenic mechanisms of PFBC, which collectively point toward a compromised neurovascular unit.

SUMMARY

The ongoing clinical and molecular research increases our understanding of PFBC facilitating diagnosis and identifying potential therapeutic targets for this multifaceted and likely underdiagnosed condition.

MYORG Mutation Heterozygosity Is Associated With Brain Calcification

BACKGROUND

Biallelic mutations in the MYORG gene were first identified as the cause of recessively inherited primary familial brain calcification. Interestingly, some heterozygous carriers also exhibited brain calcifications.

OBJECTIVES

To further investigate the role of single heterozygous MYORG mutations in the development of brain calcifications.

METHODS

A nation-wide cohort of Chinese primary familial brain calcification probands was enrolled from March 2016 through September 2019. Mutational analysis of MYORG was performed in 435 primary familial brain calcification probands who were negative for mutations in the other four known primary familial brain calcification-causative genes (SLC20A2, PDGFRB, PDGFB, and XPR1).

RESULTS

Biallelic MYORG mutations were identified in 14 primary familial brain calcification patients from 10 unrelated families. Interestingly, 12 heterozygous carriers from seven of these families also exhibited mild-to-moderate brain calcifications. Moreover, single heterozygous mutations were detected in an additional 9 probands and in 7 of their family members affected with brain calcifications. In our cohort, clinical and imaging penetrance of individuals with biallelic mutations were 100%, whereas among individuals with heterozygous mutations, penetrance of imaging phenotype was reduced to 73.7% (28 of 38) and clinical penetrance was much lower. Most (34 of 38) remained asymptomatic whereas 4 carriers had symptoms of uncertain clinical significance (nonspecific depression, epilepsy and late-onset parkinsonism). Compared with individuals with biallelic MYORG mutations, individuals with heterozygous mutations had brain calcifications with much lower calcification scores (P < 2e-16).

CONCLUSIONS

Presence of brain calcifications in individuals with heterozygous MYORG mutations suggested a semidominant inheritance pattern with incomplete penetrance. This finding further expanded the genotype-phenotype correlations of MYORG-related primary familial brain calcification. © 2020 International Parkinson and Movement Disorder Society.

Basal ganglia calcifications (Fahr's syndrome): related conditions and clinical features

Basal ganglia calcifications could be incidental findings up to 20% of asymptomatic patients undergoing CT or MRI scan. The presence of neuropsychiatric symptoms associated with bilateral basal ganglia calcifications (which could occur in other peculiar brain structures, such as dentate nuclei) identifies a clinical picture defined as Fahr's Disease. This denomination mainly refers to idiopathic forms in which no metabolic or other underlying causes are identified. Recently, mutations in four different genes (SLC20A2, PDGFRB, PDGFB, and XPR1) were identified, together with novel mutations in the Myogenic Regulating Glycosylase gene, causing the occurrence of movement disorders, cognitive decline, and psychiatric symptoms. On the other hand, secondary forms, also identified as Fahr's syndrome, have been associated with different conditions: endocrine abnormalities of PTH, such as hypoparathyroidism, other genetically determined conditions, brain infections, or toxic exposure. The underlying pathophysiology seems to be related to an abnormal calcium/phosphorus homeostasis and transportation and alteration of the blood-brain barrier.

Primary familial brain calcifications

Primary familial brain calcification (PFBC) is a neurodegenerative disease with characteristic calcium deposits in the basal ganglia and other brain regions. The disease usually presents as a combination of abnormal movements, cognitive and psychiatric manifestations, clinically indistinguishable from other adult-onset neurodegenerative disorders. The differential diagnosis must be established with genetic and nongenetic disorders that can also lead to calcium deposits in encephalic structures. In the past years PFBC causal mutations have been discovered in genes related to calcium phosphate homeostasis (SLC20A2, XPR1) and in genes involved with endothelial function and integrity (PDGFB, PDGFRB). The most frequently mutated gene is SLC20A2, where mutations can affect any domain of the protein. There is no clearcut relationship between the specific mutation/gene, onset age, neuroimaging pattern, and severity of clinical manifestations. The discovery of the genetic basis of PFBC provides not only a diagnostic tool, but also an insight into the pathomechanisms and potential therapeutic trials for this rare disease.

Mutation screening of PDGFB gene in Chinese population with primary familial brain calcification

BACKGROUND

Until recently, primary familial brain calcification (PFBC) has been determined by four genes, SLC20A2, PDGFRB, PDGFB and XPR1. No studies have been carried out to analyze the gene mutation of PDGFB in Chinese population.

OBJECTIVE

To screen mutations of PDGFB gene in a large cohort of Chinese PFBC patients with no SLC20A2 mutations.

METHODS

We recruited 192 PFBC patients, including 21 index cases and 171 sporadic cases, in our study. Peripheral venous blood samples of all included participants were collected for genomic DNA extraction. The coding sequence of PDGFB was amplified by polymerase chain reaction (PCR) followed by direct sequencing. The potential effects of the identified variants on protein function were assessed by bioinformatics analysis.

RESULTS

Three missense variants (c.35G>T, c.232C>T, and c.610C>A) and one nonsense variant (c.220G>T) of PDGFB were identified in five sporadic PFBC patients. The variant c.35G>T was found in 2 healthy controls from the same ethnic background, whereas c.220G>T, c.232C>T and c.610C>A were absent from 500 controls. c.220G>T (p.E74*) produced a stop codon in the place of the glutamicacid residue number 74. c.232C>T (p.R78C) occurred at highly conserved regions and were predicted as damaging by at least two computational predictive programs, suggesting that this variant were likely to have a causal role in PFBC. Although variant c.610C>A (p.P204T) also occurred at a highly conserved region, it was predicted to be most likely benign by two computational predictive programs, suggesting an uncertain role of this variant on PFBC.

CONCLUSIONS

The present study identified one likely pathogenic variant (p.E74*) and two variants of uncertain significance (p.R78C and p.P204T) in PDGFB. Further studies of PDGF-B functional expression for these variants are still required to confirm the pathogenic effect.

Primary familial brain calcification in the 'IBGC2' kindred: All linkage roads lead to SLC20A2

BACKGROUND

Linkage analyses of families with primary familial brain calcification (formerly idiopathic basal ganglia calcification [IBGC]) identified 3 candidate loci (IBGC1-3). Recently, SLC20A2 mutations were found in the IBGC1 and IBGC3 families, merging these 2 loci. We here elucidate the genetic cause of primary familial brain calcification in the 'IBGC2' kindred.

METHODS

We sequenced known primary familial brain calcification genes and quantified SLC20A2 and PDGFB. Moreover, CT scans of affected and unaffected family members were evaluated by 2 blinded neuroradiologists for distribution of brain calcification.

RESULTS

A heterozygous multiexonic SLC20A2 deletion was detected in several affected family members. A reevaluation of neuroimaging data revealed a subset of mutation-negative individuals with only mild and/or unilateral calcification.

CONCLUSIONS

The identified SLC20A2 mutation resolves the genetic cause of primary familial brain calcification in the 'IBGC2' kindred, collapsing 'IBGC2' into IBGC1. We suggest an algorithm for predicting the chances of finding genetic mutations that has to be validated in further studies. Our study enhances criteria for the evaluation of neuroimaging data, contributing further to the much needed harmonization of diagnostic and research data collection in primary familial brain calcification. © 2016 International Parkinson and Movement Disorder Society.

Bilateral strio-pallido-dentate calcinosis (Fahr's disease): report of seven cases and revision of literature

BACKGROUND

Fahr's disease is rare a neurodegenerative idiopathic condition characterized by symmetric and bilateral calcifications of basal ganglia, usually associated with progressive neuropsychiatric dysfunctions and movement disorders. The term "Fahr's syndrome" is used in presence of calcifications secondary to a specific cause, but the variability of etiology, pathogenesis, and clinical picture underlying this condition have raised the question of the real existence of a syndrome. Several classifications based on the etiology, the location of brain calcifications and the clinical presentation have been proposed. Here we describe seven clinical cases of basal ganglia calcifications, in order to search for pathognomonic features and correlations between clinical picture and imaging findings.

CASES PRESENTATION

The patients came to our attention for different reasons (most of them for memory/behavior disturbances); all underwent neuro-psychologic evaluation and neuro-imaging. All patients showed variable degrees of deterioration in cognitive function; anxiety and depression were frequent too, and resistant to treatment in all cases. Less frequent, but severe if present, were psychotic symptoms, with different grade of structure and emotional involvement, and always resistant to treatment. We observed only few cases of extrapyramidal disorders related to the disease itself; anyway, mild extrapyramidal syndrome occurred quite frequently after treatment with antipsychotics.

CONCLUSION

Based on these findings we discourage the use of the term "Fahr's syndrome", and suggest to refer to Idiopathic or Secondary basal ganglia calcification. Unlike early onset forms (idiopathic or inherited), the clinical presentation of late onset form and Secondary basal ganglia calcification seems to be really heterogeneous. Case-control studies are necessary to determine the actual significance of basal ganglia calcification in the adult population and in the elderly, in cognitive, physical and emotional terms.

Familial idiopathic basal ganglia calcification: Histopathologic features of an autopsied patient with an SLC20A2 mutation

Idiopathic basal ganglia calcification (IBGC), or Fahr's disease, is a neurological disorder characterized by widespread calcification in the brain. Recently, several causative genes have been identified, but the histopathologic features of the brain lesions and expression of the gene products remain unclear. Here, we report the clinical and autopsy features of a 62-year-old Japanese man with familial IBGC, in whom an SLC20A2 mutation was identified. The patient developed mild cognitive impairment and parkinsonism. A brain CT scan demonstrated abnormal calcification in the bilateral basal ganglia, thalami and cerebellum. An MRI study at this point revealed glioblastoma, and the patient died 6 months later. At autopsy, symmetric calcification in the basal ganglia, thalami, cerebellar white matter and deeper layers of the cerebral cortex was evident. The calcification was observed in the tunica media of small arteries, arterioles and capillaries, but not in veins. Immunohistochemistry using an antibody against type III sodium-dependent phosphate transporter 2 (PiT-2), the SLC20A2 product, demonstrated that astrocytic processes were labeled in several regions in control brains, whereas in the patient, reactivity in astrocytes was apparently weak. Immunoblotting demonstrated a marked decrease of PiT-2 in the patient. There are few autopsy reports of IBGC patients with confirmation of the genetic background. The autopsy features seem informative for better understanding the histogenesis of IBGC lesions.

Genetics and molecular biology of brain calcification

Brain calcification is a common neuroimaging finding in patients with neurological, metabolic, or developmental disorders, mitochondrial diseases, infectious diseases, traumatic or toxic history, as well as in otherwise normal older people. Patients with brain calcification may exhibit movement disorders, seizures, cognitive impairment, and a variety of other neurologic and psychiatric symptoms. Brain calcification may also present as a single, isolated neuroimaging finding. When no specific cause is evident, a genetic etiology should be considered. The aim of the review is to highlight clinical disorders associated with brain calcification and provide summary of current knowledge of diagnosis, genetics, and pathogenesis of brain calcification.

The genetics of primary familial brain calcifications

Bilateral accumulation of calcium in the brain, most commonly in the basal ganglia, but also in the cerebellum, thalamus, and brainstem can be inherited in an autosomal dominant fashion and is then referred to as primary familial brain calcifications (PFBC). Clinical manifestations include a spectrum of movement disorders and neuropsychiatric abnormalities. In the past 2 years, 3 genes have been identified to cause PFBC, (ie, SLC20A2, PDGFRB, and PDGFB). SCL20A2 encodes the Type III sodium-dependent inorganic phosphate (Pi) transporter 2 (PiT2) and, when mutated, uptake of Pi is severely impaired likely causing buildup of calcium phosphate. The second identified cause of PFBC is mutations in PDGFRB, which codes for platelet-derived growth factor receptor β (PDGF-Rβ). Interestingly, the third PFBC gene is PDGFB that encodes the ligand of PDGF-Rβ, which is secreted during angiogenesis to recruit pericytes, thereby implying impairment of the blood-brain barrier as a disease mechanism of PFBC.

SLC20A2 and THAP1 deletion in familial basal ganglia calcification with dystonia

Idiopathic basal ganglia calcification (IBGC) is characterized by bilateral calcification of the basal ganglia associated with a spectrum of neuropsychiatric and motor syndromes. In this study, we set out to determine the frequency of the recently identified IBGC gene SLC20A2 in 27 IBGC cases from the Mayo Clinic Florida Brain Bank using both Sanger sequencing and TaqMan copy number analysis to cover the complete spectrum of possible mutations. We identified SLC20A2 pathogenic mutations in two of the 27 cases of IBGC (7 %). Sequencing analysis identified a p.S113* nonsense mutation in SLC20A2 in one case. TaqMan copy number analysis of SLC20A2 further revealed a genomic deletion in a second case, which was part of a large previously reported Canadian IBGC family with dystonia. Subsequent whole-genome sequencing in this family revealed a 563,256-bp genomic deletion with precise breakpoints on chromosome 8 affecting multiple genes including SLC20A2 and the known dystonia-related gene THAP1. The deletion co-segregated with disease in all family members. The deletion of THAP1 in addition to SLC20A2 in the Canadian IBGC family may contribute to the severe and early onset dystonia in this family. The identification of an SLC20A2 genomic deletion in a familial form of IBGC demonstrates that reduced SLC20A2 in the absence of mutant protein is sufficient to cause neurodegeneration and that previously reported SLC20A2 mutation frequencies may be underestimated.

Fahr's syndrome: literature review of current evidence

Fahr’s disease or Fahr’s syndrome is a rare, neurological disorder characterized by abnormal calcified deposits in basal ganglia and cerebral cortex. Calcified deposits are made up of calcium carbonate and calcium phosphate, and are commonly located in the Basal Ganglia, Thalamus, Hippocampus, Cerebral cortex, Cerebellar Subcortical white matter and Dentate Nucleus. Molecular genetics of this disease haven’t been studied extensively; hence evidence at the molecular and genetic level is limited. Fahr’s disease commonly affects young to middle aged adults. Etiology of this syndrome does not identify a specific agent but associations with a number of conditions have been noted; most common of which are endocrine disorders, mitochondrial myopathies, dermatological abnormalities and infectious diseases. Clinical manifestations of this disease incorporate a wide variety of symptoms, ranging from neurological symptoms of extrapyramidal system to neuropsychiatric abnormalities of memory and concentration to movement disorders including Parkinsonism, chorea and tremors amongst others. Diagnostic criteria for this disease has been formulated after modifications from previous evidence and can be stated briefly, it consist of bilateral calcification of basal ganglia, progressive neurologic dysfunction, absence of biochemical abnormalities, absence of an infectious, traumatic or toxic cause and a significant family history. Imaging modalities for the diagnosis include CT, MRI, and plain radiography of skull. Other investigations include blood and urine testing for hematologic and biochemical indices. Disease is as yet incurable but management and treatment strategies mainly focus on symptomatic relief and eradication of causative factors; however certain evidence is present to suggest that early diagnosis and treatment can reverse the calcification process leading to complete recovery of mental functions. Families with a known history of Fahr’s disease should be counseled prior to conception so that the birth of affected babies can be prevented. This review was written with the aim to remark on the current substantial evidence surrounding this disease.

Psychosis revealing familial idiopathic basal ganglia calcification

We describe the case of a 39-year-old woman presenting with auditory hallucinations and delusions responsive to antipsychotic drugs. Computerized tomography scans revealed basal ganglia calcifications in the proband and in her two asymptomatic parents. Extensive etiological clinicobiological assessment allowed us to exclude known causes of brain calcifications and diagnose familial idiopathic basal ganglia calcification (IBGC). Neurological symptoms associated with psychiatric symptoms are common in IBGC. Nevertheless, purely psychiatric presentations, as demonstrated by the present case, are possible. However, a fortuitous association between asymptomatic IBGC and schizophrenia cannot be ruled out. Only brain imaging, followed by an extensive etiological assessment, allows for diagnosis of this rare disorder.

Novel SLC20A2 mutations identified in southern Chinese patients with idiopathic basal ganglia calcification

Idiopathic basal ganglia calcification (IBGC) is a rare neuropsychiatric disorder characterized by bilateral and symmetric cerebral calcifications. Recently, SLC20A2 was identified as a causative gene for familial IBGC, and three mutations were reported in a northern Chinese population. Here, we aimed to explore the mutation spectrum of SLC20A2 in a southern Chinese population. Sanger sequencing was employed to screen mutations within SLC20A2 in two IBGC families and 14 sporadic IBGC cases from a southern Han Chinese population. Four novel mutations (c.82G>A p.D28N, c.185T>C p.L62P, c.1470_1478delGCAGGTCCT p.Q491_L493del and c.935-1G>A) were identified in two families and two sporadic cases, respectively; none were detected in 200 unrelated controls. No mutation was found in the remaining 12 patients. Different mutations may result in varied phenotypes, including brain calcification and clinical manifestations. Our study supports the hypothesis that SLC20A2 is a causative gene of IBGC and expands the mutation spectrum of SLC20A2, which facilitates the understanding of the genotype-phenotype correlation of IBGC.

Association between a novel mutation in SLC20A2 and familial idiopathic basal ganglia calcification

Familial idiopathic basal ganglia calcification (FIBGC) is a rare, autosomal dominant disorder involving bilateral calcification of the basal ganglia. To identify gene mutations related to a Chinese FIBGC lineage, we evaluated available individuals in the family using CT scans. DNA was extracted from the peripheral blood of available family members, and both exonic and flanking intronic sequences of the SLC20A2 gene were amplified by PCR and then sequenced. Non-denaturing polyacrylamide gel electrophoresis (PAGE) was used to confirm the presence of mutations. Allele imbalances of the SLC20A2 gene or relative quantity of SLC20A2 transcripts were evaluated using qRT-PCR. A novel heterozygous single base-pair deletion (c.510delA) within the SLC20A2 gene was identified. This deletion mutation was found to co-segregate with basal ganglia calcification in all of the affected family members but was not detected in unaffected individuals or in 167 unrelated Han Chinese controls. The mutation will cause a frameshift, producing a truncated SLC20A2 protein with a premature termination codon, most likely leading to the complete loss of function of the SLC20A2 protein. This mutation may also lead to a reduction in SLC20A2 mRNA expression by approximately 30% in cells from affected individuals. In conclusion, we identified a novel mutation in SLC20A2 that is linked to FIBGC. In addition to the loss of function at the protein level, decreasing the expression of SLC20A2 mRNA may be another mechanism that can regulate SLC20A2 function in IBGC individuals. We propose that the regional expression pattern of SLC20A1 and SLC20A2 might explain the unique calcification pattern observed in FIBGC patients.

Mutations in SLC20A2 are a major cause of familial idiopathic basal ganglia calcification

Familial idiopathic basal ganglia calcification (IBGC) or Fahr's disease is a rare neurodegenerative disorder characterized by calcium deposits in the basal ganglia and other brain regions, which is associated with neuropsychiatric and motor symptoms. Familial IBGC is genetically heterogeneous and typically transmitted in an autosomal dominant fashion. We performed a mutational analysis of SLC20A2, the first gene found to cause IBGC, to assess its genetic contribution to familial IBGC. We recruited 218 subjects from 29 IBGC-affected families of varied ancestry and collected medical history, neurological exam, and head CT scans to characterize each patient's disease status. We screened our patient cohort for mutations in SLC20A2. Twelve novel (nonsense, deletions, missense, and splice site) potentially pathogenic variants, one synonymous variant, and one previously reported mutation were identified in 13 families. Variants predicted to be deleterious cosegregated with disease in five families. Three families showed nonsegregation with clinical disease of such variants, but retrospective review of clinical and neuroimaging data strongly suggested previous misclassification. Overall, mutations in SLC20A2 account for as many as 41% of our familial IBGC cases. Our screen in a large series expands the catalog of SLC20A2 mutations identified to date and demonstrates that mutations in SLC20A2 are a major cause of familial IBGC. Non-perfect segregation patterns of predicted deleterious variants highlight the challenges of phenotypic assessment in this condition with highly variable clinical presentation.

Decreased bioelements content in the hair of patients with Fahr's disease (idiopathic bilateral calcification in the brain)

The remarkable calcification of the basal ganglia and cerebellum has been traditionally called Fahr's disease, but this nomenclature is criticized for including heterogeneous diseases. To determine the pattern of some biological metals in the hair of patients with Fahr's disease, we investigated the levels of 24 bioelements in the hair of 28 patients (17 males and 11 females) with Fahr's disease and compared them with those of three age-, sex-, and living region-matched controls (84 controls in total). Interestingly, we found decreases in the levels of several bioelements [calcium (Ca), copper (Cu), iron (Fe), mercury (Hg), iodine (I), nickel (Ni), phosphate (P), lead (Pb), and selenium (Se)] in the hair of patients. This is in contrast to our previous finding of increases of Cu, Fe, zinc (Zn), and magnesium (Mg) in the cerebrospinal fluid (CSF) of patients. The decreased level of Cu in the hair was the most prominent and pathognomonic, while the increased level of Cu in the CSF had been found to be the most significant in patients. More significant correlations between two bioelements in the hair were recognized in patients than controls. Although Fahr's disease has been considered to be a heterogenous entity, the significant tendencies of several bioelements in the hair of patients in this study suggest metabolic disorders of bioelements, especially biometals, on the background. Some transporters, especially P transporter such as PiT2, of bioelements will be involved in the different distribution of bioelements in the body of patients.

Analysis of the CTAGE5 P521A variation with the risk of familial idiopathic basal ganglia calcification in an Iranian population

Familial idiopathic basal ganglia calcification (IBGC) is a rare neurodegenerative syndrome with an autosomal dominant pattern of inheritance which is characterized by deposition of calcium in the basal ganglia and other brain regions. Linkage studies demonstrated its genetic heterogeneity; however, the responsible genes are unknown. Recently, a heterozygous variation (C>G, P521A) at exon 20 of the human cutaneous T cell lymphoma-associated antigen 5 (CTAGE5) gene was found in all patients of the affected large American family linked to IBGC1 (14q11.2-21.3). However, no carrier was detected in the two affected Brazilian families. This study was performed to investigate whether the CTAGE5 P521A variation is associated with the IBGC in an affected Iranian family. Genotyping of the CTAGE5 P521A variation was determined using PCR-RFLP. Totally, 22 members of an affected Iranian family as well as 100 normal people as control group were screened. All the samples including 22 members of the affected family as well as all control people had normal CC genotype and no GC carrier was found. Our result is similar to a Brazilian study but contrary to an American report, strengthening genetic heterogeneity of this syndrome. It seems that additional studies are necessary to confirm the pathogenicity of this rare mutation.

Strio-pallido-dentate calcinosis: a diagnostic approach in adult patients

Familial idiopathic bilateral strio-pallido-dentate calcinosis is a rare autosomal dominant disorder characterized by massive symmetric calcification, detectable by CT, into the globus pallidus and striatum, with or without the involvement of the dentate nucleus, thalamus and white matter in the absence of alterations of calcium metabolism. Clinically, it has been associated with movement and/or neuropsychiatric disorders with age at onset typically in the fourth or fifth decade. Other sporadic or familial diseases can be responsible for brain calcifications with a similar anatomic strio-pallidal or strio-pallido-dentate pattern and, a restricted number of them, for neurological symptoms with onset in adulthood. Moreover, physiological age-related basal ganglia calcifications are often incidentally found, although with a far different CT aspect, in elderly patients with movement disorders. Indentifying familial and idiopathic cases may offer the opportunity to study the molecular mechanisms underlying this minerals deposition.

Exclusion of linkage to chromosomes 14q, 2q37 and 8p21.1-q11.23 in a Serbian family with idiopathic basal ganglia calcification

In this study we report clinical and imaging data from a multigenerational Serbian family with idiopathic basal ganglia calcification (IBGC) and exclusion of linkage to chromosome 14q, 2q37 and 8p21.1-q11.23. Fourteen out of 18 family members were personally examined and 11 of them were scanned with computed tomography (CT). CT scans revealed existence of symmetrical calcifications in six family members from three generations (four symptomatic and two asymptomatic). Age at onset of clinical symptoms varied between 22.0 and 55.4 years. The main clinical findings included parkinsonism, severe gait disturbances with freezing of gait, and dyskinesia. Hyperechogenicities identified by transcranial sonography corresponded well to the CT images of hyperintense calcifications in the same structures, whereas brain perfusion single photon emission computed tomography demonstrated predominant hypoperfusion in the frontal cortex and the basal ganglia. After exclusion of linkage to known loci, our pedigree with IBGC further demonstrates locus heterogeneity in this disorder. Analysis of clinically affected individuals supports observation that the clinical features of IBGC appear to be varied both within and between families. The age at onset of the clinical symptoms appeared to be decreasing in two observed transmissions, suggestive of possible genetic anticipation.

Identification of a novel genetic locus on chromosome 8p21.1-q11.23 for idiopathic basal ganglia calcification

Idiopathic basal ganglia calcification (IBGC) is a neurodegenerative disorder that is characterized by basal ganglia and extrabasal ganglia calcification, and usually inherited in an autosomal dominant pattern. To date, two genetic loci for IBGC were identified on chromosomes 14q and 2q, but further genetic heterogeneity clearly exists. In this study, a large Chinese family with autosomal dominant IBGC was characterized. Linkage analysis excluded the 14q13 and 2q37 loci. The large family was then characterized by genome-wide linkage analysis to identify a novel genetic locus for IBGC. Significant linkage was identified with markers on chromosome 8p21.1-q11.23 with a maximum LOD score of 4.10. Fine mapping defined the new genetic locus within a 25 Mb region between markers D8S1809 and D8S1833. Future studies of the candidate genes at the 8p21.1-q11.23 locus may lead to identification of a disease-causing gene with IBGC.