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

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.

Pediatric Idiopathic Basal Ganglia Calcification and Spherocytosis With Chromosome 8p11 Deletion

Idiopathic basal ganglia calcification (IBGC), also known as Fahr disease, is a rare neurodegenerative disorder characterized by the accumulation of extensive parenchymal and vascular calcifications in the basal ganglia, with variable calcifications elsewhere in the brain. Typically, IBGC presents with neurologic and psychiatric symptoms in middle-aged adults. Recent genetic studies have identified alterations in 4 genes causing IBGC, including alterations in SLC20A2 on chromosome 8p11.2. Currently, there are no clinical descriptions of patients with IBGC occurring within the context of a complex genetic syndrome. Here, we present a case of pediatric 8p11 deletion with IBGC, hereditary spherocytosis, vitreoretinopathy, and focal cortical dysplasia. We review multiple cases of IBGC with pediatric onset due to SLC20A2 deletion in the literature, and raise the consideration of IBGC in the evaluation of pediatric patients with 8p11.2 deletion syndromes.

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.

Mechanisms of calcification in Fahr disease and exposure of potential therapeutic targets

Purpose of review

There is growing interest in disorders involved in ectopic mineralization. Fahr disease or idiopathic basal ganglia calcification can serve as a model for ectopic mineralization in the basal ganglia, which is fairly common in the general population. In this review, we will focus on causative gene mutations and corresponding pathophysiologic pathways in Fahr disease.

Recent findings

Patients with Fahr disease have a variability of symptoms, such as movement disorders, psychiatric signs, and cognitive impairment, but can also be asymptomatic. Fahr disease is mostly autosomal dominant inherited, and there are mutations found in 4 causative genes. Mutations in SLC20A2 and XPR1 lead to a disrupted phosphate metabolism involving brain-specific inorganic phosphate transporters. Mutations in PDGFB and PDGFRB are associated with disrupted blood-brain barrier integrity and dysfunctional pericyte maintenance. In addition, the MYORG gene has recently been discovered to be involved in the autosomal recessive inheritance of Fahr.

Summary

Knowledge about the mutations and corresponding pathways may expose therapeutic opportunities for patients with Fahr disease and vascular calcifications in the brain in general.

Bilateral Basal Ganglia Calcification: Fahr's Disease

Fahr's disease/syndrome is a condition defined as bilateral striato-pallido-dentate calcinosis, a neurodegenerative disease with radiological findings of symmetrical and bilateral idiopathic calcifications of the cerebellum, periventricular white matter, and basal ganglia. Clinical correlation with radiological and a calcium metabolism panel is crucial in differentiating between Fahr's disease and Fahr's syndrome. We describe a case that presented with the clinical feature of a cerebrovascular accident and had an incidental radiological finding of Fahr syndrome. The clinical features, laboratory investigations, and clinical management of Fahr's disease/syndrome will be discussed in detail in the article.

A Novel SLC20A2 Mutation Associated with Familial Idiopathic Basal Ganglia Calcification and Analysis of the Genotype-Phenotype Association in Chinese Patients

BACKGROUND

Idiopathic basal ganglia calcification (IBGC) is a genetic disorder characterized by bilateral basal ganglia calcification and neural degeneration. In this study, we reported a new SLC2OA2 mutation of IBGC and reviewed relevant literature to explore the association between phenotypes and genotypes in Chinese IBGC patients.

METHODS

Clinical information of the proband and her relatives were collected comprehensively. Blood samples of both the patient and her father were obtained, and genetic screening related to IBGC was performed using second generation sequencing with their consent. Findings were confirmed by Sanger sequencing. Polyphen-2 was used to predict the potential association between mutations and disease. Then, we retrieved literatures of Chinese IBGC patients and explored the association between phenotype and genotype.

RESULTS

A novel mutation was identified through genetic testing, and it is suggested to be a damage mutation predicted by Polyphen-2. Through literature review, we found that SLC20A2 mutation is the most common cause for IBGC in China. Its hot spot regions are mainly on the 1st and 8th exons; the second common one is PDGFB where the hot spot covered a length of 220-230 bp localized on the 2nd exon; moreover, Chinese IBGC patients featured early-onset, more severe movement disorder and relatively mild cognitive impairment compared with those in other countries.

CONCLUSIONS

There is significant heterogeneity both in phenotype and genotype in Chinese IBGC patients. Further research of pathogenic mechanism of IBGC is required to eventually develop precise treatment for individuals who suffered this disease.

Developmental neurogenetics and multimodal neuroimaging of sex differences in autism

Examining sex differences in the brain has been historically contentious but is nonetheless important for advancing mental health for both girls and boys. Unfortunately, females in biomedical research remain underrepresented in most mental health conditions including autism spectrum disorders (ASD), even though equal inclusion of females would improve treatment for girls and yield benefits to boys. This review examines sex differences in the relationship between neuroanatomy and neurogenetics of ASD. Recent findings reveal that girls diagnosed with ASD exhibit more intellectual and behavioral problems compared to their male counterparts, suggesting that girls may be less likely diagnosed in the absence of such problems or that they require a higher mutational load to meet the diagnostic criteria. Thus far, the female biased effect of chromosome 4, 5p15.33, 8p, 9p24.1, 11p12-13, 15q, and Xp22.3 and the male biased effect of 1p31.3, 5q12.3, 7q, 9q33.3, 11q13.4, 13q33.3, 16p11.2, 17q11-21, Xp22.33/Yp11.31, DRD1, NLGN3, MAOA, and SHANK1 deletion have been discovered in ASD. The SNPs of genes such as RYR2, UPP2, and the androgen receptor gene have been shown to have sex-biasing factors in both girls and boys diagnosed with ASD. These sex-related genetic factors may drive sex differences in the neuroanatomy of these girls and boys, including abnormal enlargement in temporal gray and white matter volumes, and atypical reduction in cerebellar gray matter volumes and corpus callosum fibers projecting to the anterior frontal cortex in ASD girls relative to boys. Such factors may also be responsible for the attenuation of brain sexual differentiation in adult men and women with ASD; however, much remains to be uncovered or replicated. Future research should leverage further the association between neuroanatomy and genetics in girls for an integrated and interdisciplinary understanding of ASD.

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.

Primary familial brain calcification linked to deletion of 5' noncoding region of SLC20A2

OBJECTIVES

Primary familial brain calcification (PFBC) is a rare neurological disease often inherited as a dominant trait. Mutations in four genes (SLC20A2, PDGFB, PDGFRB, and XPR1) have been reported in patients with PFBC. Of these, point mutations or small deletions in SLC20A2 are most common. Thus far, only one large deletion covering entire SLC20A2 and several smaller, exonic deletions of SLC20A2 have been reported. The aim of this study was to identify the causative gene defect in a Finnish PFBC family with three affected patients.

MATERIALS AND METHODS

A Finnish family with three PFBC patients and five unaffected subjects was studied. Sanger sequencing was used to exclude mutations in the coding and splice site regions of SLC20A2, PDGFRB, and PDGFB. Whole-exome (WES) and whole-genome sequencing (WGS) were performed to identify the causative mutation. A SNP array was used in segregation analysis.

RESULTS

Copy number analysis of the WGS data revealed a heterozygous deletion of ~578 kb on chromosome 8. The deletion removes the 5' UTR region, the noncoding exon 1 and the putative promoter region of SLC20A2 as well as the coding regions of six other genes.

CONCLUSIONS

Our results support haploinsufficiency of SLC20A2 as a pathogenetic mechanism in PFBC. Analysis of copy number variations (CNVs) is emerging as a crucial step in the molecular genetic diagnostics of PFBC, and it should not be limited to coding regions, as causative variants may reside in the noncoding parts of known disease-associated genes.

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.

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.

Primary dystonias and genetic disorders with dystonia as clinical feature of the disease

Dystonia is probably the most common form of movement disorder encountered in the clinical practice. It is characterized by sustained muscle contractions, usually producing twisting and repetitive movements or abnormal postures or positions. Dystonias can be classified in several ways, including primarily by the clinical phenomenology or by the underlining etiology, in particular to understand if the presentation is genetically determined. By advances of genetics, including contemporary genomic technologies, there is a growing understanding of the molecular underpinnings of genetically determined dystonias. The intricacy of information requires a user friendly, novel database that may efficiently serve clinicians to inform of advances of the field and to diagnose and manage these often complex cases. Here we present an up to date, comprehensive review - in tabulated formats - of genetically determined primary dystonias and complex Mendelian disorders with dystonia as central feature. The detailed search up to December 24, 2012, identified 24 hereditary primary dystonias (DYT1 to DYT 25) that are mostly monogenic disorders, and a larger group (>70) of genetic syndromes in which dystonia is one of the characteristic clinical features. We organized the findings not only by individual information (name of the conditions, pattern of inheritance, chromosome and gene abnormality, clinical features, relevant ancillary tests and key references), but also provide symptom-oriented organization of the clinical entities for efficient inquiries.

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.

Phenotypic spectrum of probable and genetically-confirmed idiopathic basal ganglia calcification

Idiopathic basal ganglia calcification is characterized by mineral deposits in the brain, an autosomal dominant pattern of inheritance in most cases and genetic heterogeneity. The first causal genes, SLC20A2 and PDGFRB, have recently been reported. Diagnosing idiopathic basal ganglia calcification necessitates the exclusion of other causes, including calcification related to normal ageing, for which no normative data exist. Our objectives were to diagnose accurately and then describe the clinical and radiological characteristics of idiopathic basal ganglia calcification. First, calcifications were evaluated using a visual rating scale on the computerized tomography scans of 600 consecutively hospitalized unselected controls. We determined an age-specific threshold in these control computerized tomography scans as the value of the 99th percentile of the total calcification score within three age categories: <40, 40-60, and >60 years. To study the phenotype of the disease, patients with basal ganglia calcification were recruited from several medical centres. Calcifications that rated below the age-specific threshold using the same scale were excluded, as were patients with differential diagnoses of idiopathic basal ganglia calcification, after an extensive aetiological assessment. Sanger sequencing of SLC20A2 and PDGFRB was performed. In total, 72 patients were diagnosed with idiopathic basal ganglia calcification, 25 of whom bore a mutation in either SLC20A2 (two families, four sporadic cases) or PDGFRB (one family, two sporadic cases). Five mutations were novel. Seventy-one per cent of the patients with idiopathic basal ganglia calcification were symptomatic (mean age of clinical onset: 39 ± 20 years; mean age at last evaluation: 55 ± 19 years). Among them, the most frequent signs were: cognitive impairment (58.8%), psychiatric symptoms (56.9%) and movement disorders (54.9%). Few clinical differences appeared between SLC20A2 and PDGFRB mutation carriers. Radiological analysis revealed that the total calcification scores correlated positively with age in controls and patients, but increased more rapidly with age in patients. The expected total calcification score was greater in SLC20A2 than PDGFRB mutation carriers, beyond the effect of the age alone. No patient with a PDGFRB mutation exhibited a cortical or a vermis calcification. The total calcification score was more severe in symptomatic versus asymptomatic individuals. We provide the first phenotypical description of a case series of patients with idiopathic basal ganglia calcification since the identification of the first causative genes. Clinical and radiological diversity is confirmed, whatever the genetic status. Quantification of calcification is correlated with the symptomatic status, but the location and the severity of the calcifications don't reflect the whole clinical diversity. Other biomarkers may be helpful in better predicting clinical expression.

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.

Genetics in arterial calcification: lessons learned from rare diseases

Arterial calcification significantly contributes to morbidity and mortality. Insight into the pathophysiological mechanisms contributing to arterial calcification has come from genetic studies on four rare monogenic disorders. The disease-causing molecular defects in generalized arterial calcification of infancy (GACI), pseudoxanthoma elasticum (PXE), calcification of joints and arteries (CALJA), and familial idiopathic basal ganglia calcification (IBGC) have been identified within recent years. Based on the similarities of GACI, PXE, CALJA, and IBGC, it can be speculated that the underlying disease genes-ENPP1, ABCC6, NT5E, and SLC20A2, respectively-drive a cohesive molecular pathophysiology system modulated by ATP metabolism, inorganic pyrophosphate, adenosine, and inorganic phosphate generation and functional activities.

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.

A novel homozygous 10 nucleotide deletion in BBS10 causes Bardet-Biedl syndrome in a Pakistani family

Bardet-Biedl Syndrome is a multisystem autosomal recessive disorder characterized by central obesity, polydactyly, hypogonadism, learning difficulties, rod-cone dystrophy and renal dysplasia. Bardet-Biedl Syndrome has a prevalence rate ranging from 1 in 100,000 to 1 in 160,000 births although there are communities where Bardet-Biedl Syndrome is found at a higher frequency due to consanguinity. We report here a Pakistani consanguineous family with two affected sons with typical clinical features of Bardet-Biedl Syndrome, in addition to abnormal liver functioning and bilateral basal ganglia calcification, the latter feature being typical of Fahr's disease. Homozygous regions obtained from SNP array depicted three known genes BBS10, BBS14 and BBS2. Bidirectional sequencing of all coding exons by traditional sequencing of all these three genes showed a homozygous deletion of 10 nucleotides (c.1958_1967del), in BBS10 in both affected brothers. The segregation analysis revealed that the parents, paternal grandfather, maternal grandmother and an unaffected sister were heterozygous for the deletion. Such a large deletion in BBS10 has not been reported previously in any population and is likely to be contributing to the phenotype of Bardet-Biedl Syndrome in this family.

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.

Mutations in SLC20A2 link familial idiopathic basal ganglia calcification with phosphate homeostasis

Familial idiopathic basal ganglia calcification (IBGC) is a genetic condition with a wide spectrum of neuropsychiatric symptoms, including parkinsonism and dementia. Here, we identified mutations in SLC20A2, encoding the type III sodium-dependent phosphate transporter 2 (PiT2), in IBGC-affected families of varied ancestry, and we observed significantly impaired phosphate transport activity for all assayed PiT2 mutants in Xenopus laevis oocytes. Our results implicate altered phosphate homeostasis in the etiology of IBGC.

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.

Identification and molecular characterization of two novel mutations in COL1A2 in two Chinese families with osteogenesis imperfecta

Osteogenesis imperfecta (OI, also known as brittle bone disease) is caused mostly by mutations in two type I collagen genes, COL1A1 and COL1A2 encoding the pro-α1 (I) and pro-α2 (I) chains of type I collagen, respectively. Two Chinese families with autosomal dominant OI were identified and characterized. Linkage analysis revealed linkage of both families to COL1A2 on chromosome 7q21.3-q22.1. Mutational analysis was carried out using direct DNA sequence analysis. Two novel missense mutations, c.3350A>G and c.3305G>C, were identified in exon 49 of COL1A2 in the two families, respectively. The c.3305G>C mutation resulted in substitution of a glycine residue (G) by an alanine residue (A) at codon 1102 (p.G1102A), which was found to be mutated into serine (S), argine (R), aspartic acid (D), or valine (V) in other families. The c.3350A>G variant may be a de novo mutation resulting in p.Y1117C. Both mutations co-segregated with OI in respective families, and were not found in 100 normal controls. The G1102 and Y1117 residues were evolutionarily highly conserved from zebrafish to humans. Mutational analysis did not identify any mutation in the COX-2 gene (a modifier gene of OI). This study identifies two novel mutations p.G1102A and p.Y1117C that cause OI, significantly expands the spectrum of COL1A2 mutations causing OI, and has a significant implication in prenatal diagnosis of OI.

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.

A case of idiopathic basal ganglia calcification associated with membranoproliferative glomerulonephritis

Idiopathic basal ganglia calcification (IBGC) is a syndrome in which bilateral cerebral calcification occurs despite the absence of abnormal calcium metabolism. A 17-year-old Japanese female was admitted for investigation of intermittent proteinuria from the age of 12 years. On admission, her blood pressure was 126/60 mmHg and her serum creatinine was 0.8 mg/dL. Although computed tomography revealed bilateral striopallidodentate calcinosis, her level of intelligence and neurological findings were normal, as were the results of endocrine tests including parathyroid hormone. Asymptomatic IBGC was diagnosed. Renal biopsy showed membranoproliferative glomerulonephritis. Peritoneal dialysis was started for end-stage renal failure when she was 24 years old. Pyramidal and extrapyramidal signs started to develop at the age of 27 years and progressed, resulting in death from aspiration pneumonia at the age of 32 years. Post-mortem revealed bilateral calcification of the basal ganglia, dentate nucleus, thalamus, and centrum semiovale. On light microscopy, there was circumferential calcification of the media and intima of affected vessels in the brain, including small arteries, small veins, and capillaries, and luminal narrowing was seen. On electron microscopy, layers of differing electron density were arranged in concentric laminae. This is the first report of IBGC with bilateral and symmetrical cerebral calcification accompanied by membranoproliferative glomerulonephritis resulting in end-stage renal failure.