Mutations in SLC20A2 link familial idiopathic basal ganglia calcification with phosphate homeostasis. Nat Genet. 2012;44:254-256. [PMID: 22327515 DOI: 10.1038/ng.1077]

Targeting TREM2 signaling shows limited impact on cerebrovascular calcification

Brain calcification, the ectopic mineral deposits of calcium phosphate, is a frequent radiological finding and a diagnostic criterion for primary familial brain calcification. We previously showed that microglia curtail the growth of small vessel calcification via the triggering receptor expressed in myeloid 2 (TREM2) in the Pdgfb ret/ret mouse model of primary familial brain calcification. Because boosting TREM2 function using activating antibodies has been shown to be beneficial in other disease conditions by aiding in microglial clearance of diverse pathologies, we investigated whether administration of a TREM2-activating antibody could mitigate vascular calcification in Pdgfb ret/ret mice. Single-nucleus RNA-sequencing analysis showed that calcification-associated microglia share transcriptional similarities to disease-associated microglia and exhibited activated TREM2 and TGFβ signaling. Administration of a TREM2-activating antibody increased TREM2-dependent microglial deposition of cathepsin K, a collagen-degrading protease, onto calcifications. However, this did not ameliorate the calcification load or alter the mineral composition and the microglial phenotype around calcification. We therefore conclude that targeting microglia with TREM2 agonistic antibodies is insufficient to demineralize and clear vascular calcifications.

Antisense oligonucleotides enhance SLC20A2 expression and suppress brain calcification in a humanized mouse model

Primary familial brain calcification (PFBC) is a genetic neurological disease, yet no effective treatment is currently available. Here, we identified five novel intronic variants in SLC20A2 gene from six PFBC families. Three of these variants increased aberrant SLC20A2 pre-mRNA splicing by altering the binding affinity of splicing machineries to newly characterized cryptic exons, ultimately causing premature termination of SLC20A2 translation. Inhibiting the cryptic-exon incorporation with splice-switching ASOs increased the expression levels of functional SLC20A2 in cells carrying SLC20A2 mutations. Moreover, by knocking in a humanized SLC20A2 intron 2 sequence carrying a PFBC-associated intronic variant, the SLC20A2-KI mice exhibited increased inorganic phosphate (Pi) levels in cerebrospinal fluid (CSF) and progressive brain calcification. Intracerebroventricular administration of ASOs to these SLC20A2-KI mice reduced CSF Pi levels and suppressed brain calcification. Together, our findings expand the genetic etiology of PFBC and demonstrate ASO-mediated splice modulation as a potential therapy for PFBC patients with SLC20A2 haploinsufficiency.

Astrocytes modulate brain phosphate homeostasis via polarized distribution of phosphate uptake transporter PiT2 and exporter XPR1

Aberrant inorganic phosphate (Pi) homeostasis causes brain calcification and aggravates neurodegeneration, but the underlying mechanism remains unclear. Here, we found that primary familial brain calcification (PFBC)-associated Pi transporter genes Pit2 and Xpr1 were highly expressed in astrocytes, with importer PiT2 distributed over the entire astrocyte processes and exporter XPR1 localized to astrocyte end-feet on blood vessels. This polarized PiT2 and XPR1 distribution endowed astrocyte with Pi transport capacity competent for brain Pi homeostasis, which was disrupted in mice with astrocyte-specific knockout (KO) of either Pit2 or Xpr1. Moreover, we found that Pi uptake by PiT2, and its facilitation by PFBC-associated galactosidase MYORG, were required for the high Pi transport capacity of astrocytes. Finally, brain calcification was suppressed by astrocyte-specific PiT2 re-expression in Pit2-KO mice. Thus, astrocyte-mediated Pi transport is pivotal for brain Pi homeostasis, and elevating astrocytic Pi transporter function represents a potential therapeutic strategy for reducing brain calcification.

A Homozygous Variant in NAA60 Is Associated with Primary Familial Brain Calcification

BACKGROUND

Primary familial brain calcification (PFBC) is a monogenic disorder characterized by bilateral calcifications in the brain. The genetic basis remains unknown in over half of the PFBC patients, indicating the existence of additional novel causative genes. NAA60 was a recently reported novel causative gene for PFBC.

OBJECTIVE

The aim was to identify the probable novel causative gene in an autosomal recessive inherited PFBC family.

METHODS

We performed a comprehensive genetic study on a consanguineous Chinese family with 3 siblings diagnosed with PFBC. We evaluated the effect of the variant in a probable novel causative gene on the protein level using Western blot, immunofluorescence, and coimmunoprecipitation. Possible downstream pathogenic mechanisms were further explored in gene knockout (KO) cell lines and animal models.

RESULTS

We identified a PFBC co-segregated homozygous variant of c.460_461del (p.D154Lfs*113) in NAA60. Functional assays showed that this variant disrupts NAA60 protein localization to Golgi and accelerated protein degradation. The mutant NAA60 protein alters its interaction with the PFBC-related proteins PiT2 and XPR1, affecting intracellular phosphate homeostasis. Further mass spectrometry analysis in NAA60 KO cell lines revealed decreased expression of multiple brain calcification-associated proteins, including reduced folate carrier (RFC), a folate metabolism-related protein.

CONCLUSIONS

Our study replicated the identification of NAA60 as a novel causative gene for autosomal recessive PFBC, demonstrating our causative variant leads to NAA60 loss of function. The NAA60 loss of function disrupts not only PFBC-related proteins (eg, PiT2 and XPR1) but also a wide range of other brain calcification-associated membrane protein substrates (eg, RFC), and provided a novel probable pathogenic mechanism for PFBC. © 2024 International Parkinson and Movement Disorder Society.

Biology of bone mineralization and ectopic calcifications: the same actors for different plays

Bone has several crucial functions. It is essential for locomotion and allows our body to stand erect against gravity. A mismatch between the mechanical stresses applied to it and its mechanical resistance leads to fractures. Bone also has numerous endocrine functions. It acts as a reservoir for minerals such as calcium and phosphorus, making it the target of calciotropic hormones that mobilize these minerals, particularly calcium, according to the body's needs. Additionally, bone secretes hormones, notably fibroblast growth factor 23 (FGF23), which regulates urinary excretion of phosphate and the bioavailability of active vitamin D. Bone mineralization is the process that facilitates the organized deposition of minerals in the bone matrix, providing rigidity and appropriate mechanical resistance. This process is compromised in genetically related bone mineralization disorders, such as those causing hypophosphatemia or hypophosphatasia. Conversely, calcification can be pathological, affecting soft tissues like the blood vessels, as seen in generalized arterial calcification of infancy (GACI) or arterial calcification due to CD73 deficiency (ACDC). The aim of this article is to first present the composition and structure of the mineralized bone matrix, to review the current understanding of the molecular mechanisms of mineralization, and finally to discuss the conditions associated with ectopic calcification and the underlying mechanisms.

Global huntingtin knockout in adult mice leads to fatal neurodegeneration that spares the pancreas

Huntington's disease (HD) is a fatal neurodegenerative disorder caused by an expanded CAG tract in the huntingtin (HTT) gene, leading to toxic gains of function. HTT-lowering treatments are in clinical trials, but the risks imposed are unclear. Recent studies have reported on the consequences of widespread HTT loss in mice, where one group described early HTT loss leading to fatal pancreatitis, but later loss as benign. Another group reported no pancreatitis but found widespread neurological phenotypes including subcortical calcification. To better understand the liabilities of widespread HTT loss, we knocked out Htt with two separate tamoxifen-inducible Cre lines. We find that loss of HTT at 2 mo of age leads to progressive tremors and severe subcortical calcification at examination at 14 mo of age but does not result in acute pancreatitis or histological changes in the pancreas. We, in addition, report that HTT loss is followed by sustained induction of circulating neurofilament light chain. These results confirm that global loss of HTT in mice is associated with pronounced risks, including progressive subcortical calcification and neurodegeneration.

JAM2 variants can be more common in primary familial brain calcification (PFBC) cases than those appear; may be due to a founder mutation

INTRODUCTION

Mutations in JAM2 have been linked to ~ 2% of primary familial brain calcification (PFBC) cases. PFBC is a rare neurological disorder characterized by excessive calcium deposition in the brain. It causes movement disorders and psychiatric problems. Six other genes were identified as causing PFBC. However, the genetic basis of ~ 50% of PFBC cases remains unknown. This study presented the results of a comprehensive analysis of five unrelated Iranian PFBC families.

METHODS

Clinical and paraclinical features of all patients were recorded. Whole-exome sequencing (WES) was done on the DNAs of probands. Data was analyzed, and haplotypes were determined.

RESULTS

WES identified two homozygous variants in JAM2 across four families: a novel variant, c.426dup:p.Ser143Leufs*23, in one family and a known mutation, c.685C > T:p.Arg229*, in the remaining three families. Haplotype analysis using six intragenic single-nucleotide polymorphisms (SNPs) in JAM2 revealed an identical haplotype in probands who carried the same mutation, whereas two other probands presented diverse haplotypes.

CONCLUSION

Based on our results, p.Arg229* may be a founder mutation in the Iranian population. The variant has been detected in two out of seven other reported JAM2-related families who may originate from the Middle East and exhibit an identical haplotype. Even though this particular mutation may not be classified as a founder mutation, it does appear to be a hotspot, given that it has been observed in 45% of the 11 JAM2-associated families. Our study expanded the clinical features and mutation spectrum of JAM2 and revealed that mutations in JAM2 may be more common than previously reported.

Primary familial brain calcification presenting with parkinsonism and motor complications caused by a novel SLC20A2 variant: a case report

Primary familial brain calcification (PFBC), also known as Fahr's disease, is a central nervous system calcium deposition disorder with symmetrical basal ganglia calcification. Most PFBC cases are caused by SLC20A2 gene variant. We report a Chinese female patient with PFBC and dopamine-responsive parkinsonism who had motor fluctuations and dyskinesia and recovered effectively after symptomatic medication adjustment. A novel heterozygous missense variant was found by whole-exome sequencing and proven harmful by family validation and genetic analysis. This example expands the phenotype of SLC20A2-associated PFBC patients and shows the clinical efficacy of dopaminergic replacement treatment.

Upstream open reading frame-introducing variants in patients with primary familial brain calcification

More than 50% of patients with primary familial brain calcification (PFBC), a rare neurological disorder, remain genetically unexplained. While some causative genes are yet to be identified, variants in non-coding regions of known genes may represent a source of missed diagnoses. We hypothesized that 5'-Untranslated Region (UTR) variants introducing an AUG codon may initiate mRNA translation and result in a loss of function in some of the PFBC genes. After reannotation of exome sequencing data of 113 unrelated PFBC probands, we identified two upstream AUG-introducing variants in the 5'UTR of PDGFB. One, NM_002608.4:c.-373C>G, segregated with PFBC in the family. It was predicted to create an upstream open reading frame (ORF). The other one, NM_002608.4:c.-318C>T, was found in a simplex case. It was predicted to result in an ORF overlapping the natural ORF with a frameshift. In a GFP reporter assay, both variants were associated with a dramatic decrease in GFP levels, and, after restoring the reading frame with the GFP sequence, the c.-318C>T variant was associated with a strong initiation of translation as measured by western blotting. Overall, we found upstream AUG-introducing variants in the 5'UTR of PDGFB in 2/113 (1.7%) undiagnosed PFBC cases. Such variants thus represent a source of putative pathogenic variants.

Non-Motor Symptoms in Primary Familial Brain Calcification

Background/Objectives: Primary Familial Brain Calcification is a rare neurodegenerative disorder of adulthood characterized by calcium deposition in the basal ganglia and other brain areas; the main clinical manifestations include movement disorders, mainly parkinsonism. Non-motor symptoms are not well defined in PFBC. This work aims at defining the burden of non-motor symptoms in PFBC. Methods: A clinical, genetic and neuropsychological evaluation of a cohort of PFBC patients, COMPASS-31 scale administration. Results: A total of 50 PFBC patients were recruited; in 25, the genetic test was negative; 10 carried mutations in SLC20A2 gene, 8 in MYORG, 3 in PDGFB, 1 in PDGFRB, 2 in JAM2 (single mutations), and one test is still ongoing. The main motor manifestation was parkinsonism. Headache was reported in 26% of subjects (especially in PDGFB mutation carriers), anxiety or depression in 62%, psychosis or hallucinations in 10-12%, sleep disturbances in 34%; 14% of patients reported hyposmia, 32% constipation, and 34% urinary disturbances. A neuropsychological assessment revealed cognitive involvement in 56% (sparing memory functions, to some extent). The COMPASS-31 mean score was 20.6, with higher sub-scores in orthostatic intolerance and gastrointestinal problems. MYORG patients and subjects with cognitive decline tended to have higher scores and bladder involvement compared to other groups. Conclusions: The presence of non-motor symptoms is frequent in PFBC and should be systematically assessed to better meet patients' needs.

Novel findings in a Swedish primary familial brain calcification cohort

INTRODUCTION

Brain calcifications are frequent findings on imaging. In a small proportion of cases, these calcifications are associated with pathogenic gene variants, hence termed primary familial brain calcification (PFBC). The clinical penetrance is incomplete and phenotypic variability is substantial. This paper aims to characterize a Swedish PFBC cohort including 25 patients: 20 from seven families and five sporadic cases.

METHODS

Longitudinal clinical assessment and CT imaging were conducted, abnormalities were assessed using the total calcification score (TCS). Genetic analyses, including a panel of six known PFBC genes, were performed in all index and sporadic cases. Additionally, three patients carrying a novel pathogenic copy number variant in SLC20A2 had their cerebrospinal fluid phosphate (CSF-Pi) levels measured.

RESULTS

Among the 25 patients, the majority (76%) displayed varying symptoms during the initial assessment including motor (60%), psychiatric (40%), and/or cognitive abnormalities (24%). Clinical progression was observed in most patients (78.6%), but there was no significant difference in calcification between the first and second scans, with mean scores of 27.3 and 32.8, respectively. In three families and two sporadic cases, pathogenic genetic variants were identified, including a novel finding, in the SLC20A2 gene. In the three tested patients, the CSF-Pi levels were normal.

CONCLUSIONS

This report demonstrates the variable expressivity seen in PFBC and includes a novel pathogenic variant in the SLC20A2 gene. In four families and three sporadic cases, no pathogenic variants were found, suggesting that new PFBC genes remain to be discovered.

XPR1: a regulator of cellular phosphate homeostasis rather than a Pi exporter

Phosphate (Pi) is an essential nutrient, and its plasma levels are under tight hormonal control. Uphill transport of Pi into cells is mediated by the two Na-dependent Pi transporter families SLC34 and SLC20. The molecular identity of a potential Pi export pathway is controversial, though XPR1 has recently been suggested by Giovannini and coworkers to mediate Pi export. We expressed XPR1 in Xenopus oocytes to determine its functional characteristics. Xenopus isoforms of proteins were used to avoid species incompatibility. Protein tagging confirmed the localization of XPR1 at the plasma membrane. Efflux experiments, however, failed to detect translocation of Pi attributable to XPR1. We tested various counter ions and export medium compositions (pH, plasma) as well as potential protein co-factors that could stimulate the activity of XPR1, though without success. Expression of truncated XPR1 constructs and individual domains of XPR1 (SPX, transmembrane core, C-terminus) demonstrated downregulation of the uptake of Pi mediated by the C-terminal domain of XPR1. Tethering the C-terminus to the transmembrane core changed the kinetics of the inhibition and the presence of the SPX domain blunted the inhibitory effect. Our observations suggest a regulatory role of XPR1 in cellular Pi handling rather than a function as Pi exporter. Accordingly, XPR1 senses intracellular Pi levels via its SPX domain and downregulates cellular Pi uptake via the C-terminal domain. The molecular identity of a potential Pi export protein remains therefore elusive.

Biallelic NAA60 variants with impaired n-terminal acetylation capacity cause autosomal recessive primary familial brain calcifications

Primary familial brain calcification (PFBC) is characterized by calcium deposition in the brain, causing progressive movement disorders, psychiatric symptoms, and cognitive decline. PFBC is a heterogeneous disorder currently linked to variants in six different genes, but most patients remain genetically undiagnosed. Here, we identify biallelic NAA60 variants in ten individuals from seven families with autosomal recessive PFBC. The NAA60 variants lead to loss-of-function with lack of protein N-terminal (Nt)-acetylation activity. We show that the phosphate importer SLC20A2 is a substrate of NAA60 in vitro. In cells, loss of NAA60 caused reduced surface levels of SLC20A2 and a reduction in extracellular phosphate uptake. This study establishes NAA60 as a causal gene for PFBC, provides a possible biochemical explanation of its disease-causing mechanisms and underscores NAA60-mediated Nt-acetylation of transmembrane proteins as a fundamental process for healthy neurobiological functioning.

The pathophysiology of hypophosphatemia

After identification of fibroblast growth factor (FGF) 23 as the pivotal regulator of chronic serum inorganic phosphate (Pi) levels, the etiology of disorders causing hypophosphatemic rickets/osteomalacia has been clarified, and measurement of intact FGF23 serves as a potent tool for differential diagnosis of chronic hypophosphatemia. Additionally, measurement of bone-specific alkaline phosphatase (BAP) is recommended to differentiate acute and subacute hypophosphatemia from chronic hypophosphatemia. This article divides the etiology of chronic hypophosphatemia into 4 groups: A. FGF23 related, B. primary tubular dysfunction, C. disturbance of vitamin D metabolism, and D. parathyroid hormone 1 receptor (PTH1R) mediated. Each group is further divided into its inherited form and acquired form. Topics for each group are described, including "ectopic FGF23 syndrome," "alcohol consumption-induced FGF23-related hypophosphatemia," "anti-mitochondrial antibody associated hypophosphatemia," and "vitamin D-dependent rickets type 3." Finally, a flowchart for differential diagnosis of chronic hypophosphatemia is introduced.

Vascular Calcification: A Passive Process That Requires Active Inhibition

The primary cause of worldwide mortality and morbidity stems from complications in the cardiovascular system resulting from accelerated atherosclerosis and arterial stiffening. Frequently, both pathologies are associated with the pathological calcification of cardiovascular structures, present in areas such as cardiac valves or blood vessels (vascular calcification). The accumulation of hydroxyapatite, the predominant form of calcium phosphate crystals, is a distinctive feature of vascular calcification. This phenomenon is commonly observed as a result of aging and is also linked to various diseases such as diabetes, chronic kidney disease, and several genetic disorders. A substantial body of evidence indicates that vascular calcification involves two primary processes: a passive process and an active process. The physicochemical process of hydroxyapatite formation and deposition (a passive process) is influenced significantly by hyperphosphatemia. However, the active synthesis of calcification inhibitors, including proteins and low-molecular-weight inhibitors such as pyrophosphate, is crucial. Excessive calcification occurs when there is a loss of function in enzymes and transporters responsible for extracellular pyrophosphate metabolism. Current in vivo treatments to prevent calcification involve addressing hyperphosphatemia with phosphate binders and implementing strategies to enhance the availability of pyrophosphate.

The Association between Intracranial Calcifications and Symptoms in Patients with Primary Familial Brain Calcification

(1) Background: Primary Familial Brain Calcification (PFBC) is a neurodegenerative disease characterized by bilateral calcifications of the basal ganglia and other intracranial areas. Many patients experience symptoms of motor dysfunction and cognitive disorders. The aim of this study was to investigate the association between the amount and location of intracranial calcifications with these symptoms. (2) Methods: Patients with suspected PFBC referred to our outpatient clinic underwent a clinical work-up. Intracranial calcifications were visualized on Computed Tomography (CT), and a Total Calcification Score (TCS) was constructed. Logistic and linear regression models were performed. (3) Results: Fifty patients with PFBC were included in this study (median age 64.0 years, 50% women). Of the forty-one symptomatic patients (82.0%), 78.8% showed motor dysfunction, and 70.7% showed cognitive disorders. In multivariate analysis, the TCS was associated with bradykinesia/hypokinesia (OR 1.07, 95%-CI 1.02-1.12, p < 0.01), gait ataxia (OR 1.06, 95%-CI 1.00-1.12, p = 0.04), increased fall risk (OR 1.04, 95%-CI 1.00-1.08, p = 0.03), and attention/processing speed disorders (OR 1.06, 95%-CI 1.01-1.12, p = 0.02). Calcifications of the lentiform nucleus and subcortical white matter were associated with motor and cognitive disorders. (4) Conclusions: cognitive and motor symptoms are common among patients with PFBC, and there is an association between intracranial calcifications and these symptoms.

Slc20a1 and Slc20a2 regulate neuronal plasticity and cognition independently of their phosphate transport ability

In recent years, primary familial brain calcification (PFBC), a rare neurological disease characterized by a wide spectrum of cognitive disorders, has been associated to mutations in the sodium (Na)-Phosphate (Pi) co-transporter SLC20A2. However, the functional roles of the Na-Pi co-transporters in the brain remain still largely elusive. Here we show that Slc20a1 (PiT-1) and Slc20a2 (PiT-2) are the most abundant Na-Pi co-transporters expressed in the brain and are involved in the control of hippocampal-dependent learning and memory. We reveal that Slc20a1 and Slc20a2 are differentially distributed in the hippocampus and associated with independent gene clusters, suggesting that they influence cognition by different mechanisms. Accordingly, using a combination of molecular, electrophysiological and behavioral analyses, we show that while PiT-2 favors hippocampal neuronal branching and survival, PiT-1 promotes synaptic plasticity. The latter relies on a likely Otoferlin-dependent regulation of synaptic vesicle trafficking, which impacts the GABAergic system. These results provide the first demonstration that Na-Pi co-transporters play key albeit distinct roles in the hippocampus pertaining to the control of neuronal plasticity and cognition. These findings could provide the foundation for the development of novel effective therapies for PFBC and cognitive disorders.

One Train May Hide Another: Two Cases of Co-Occurring Primary Familial Brain Calcification and Alzheimer's Disease

Primary familial brain calcification (PFBC) is a rare disorder that can manifest with a wide spectrum of motor, cognitive, and psychiatric symptoms or even remain asymptomatic. Alzheimer disease (AD) is a common condition that typically starts as a progressive amnestic disorder and progresses to major cognitive impairment. Accurately attributing an etiology to cognitive impairment can sometimes be challenging, especially when multiple pathologies with potentially overlapping symptomatology contribute to the clinical phenotype. Here, we present the case of two patients with autosomal dominant PFBC and non-monogenic AD. Cerebrospinal fluid (CSF) biomarker analysis combined with genetic testing permitted the dual diagnosis. We emphasize the importance of thoroughly characterizing the patient's phenotype at onset and during the follow-up. Particular attention is placed on psychiatric symptoms given that both patients had a history of mood disorder, a frequent condition in the general population and in neurological diseases. We also discuss and challenge the paradigm of seeking a single diagnosis explaining all symptoms, remembering the possibility of a rare disease co-occurring with a common one.

White matter disorders with cerebral calcification in adulthood

This chapter provides a comprehensive overview of adult-onset leukoencephalopathies with cerebral calcification (CC), emphasizing the importance of age at presentation, systemic clinical features, and neuroimaging patterns for accurate diagnosis. CC is a multifaceted phenomenon associated with various neurologic, developmental, metabolic, and genetic conditions, as well as normal aging. Here, we explore the distinction between primary familial brain calcification (PFBC) and secondary forms, including metabolic and mitochondrial causes. We discuss genetic causes, e.g., SLC20A2, XPR1, PDGFB, PDGFRB, MYORG, NAA60 and JAM2, in the context of autosomal dominant and recessive PFBC and other inherited conditions. The chapter delineates the diagnostic approach involving family history, clinical assessments, and detailed investigations of calcium-phosphate metabolism. Neuroimaging modalities, including computed tomography and magnetic resonance imaging, are crucial for assessing calcification patterns and localizations. Genetic testing, especially next-generation sequencing, plays a pivotal role in providing a final molecular diagnosis. The management of patients with CC encompasses symptomatic treatment and cause-specific approaches, requiring a multidisciplinary care approach. In conclusion, this chapter highlights the complexity of leukoencephalopathies with CC, emphasizing the need for integrated and evolving management to optimize patient care.

Frequency of Hereditary and GBA1-Related Parkinsonism in Latin America: A Systematic Review and Meta-Analysis

BACKGROUND

Identifying hereditary parkinsonism is valuable for diagnosis, genetic counseling, patient prioritization in trials, and studying the disease for personalized therapies. However, most studies were conducted in Europeans, and limited data exist on admixed populations like those from Latin America.

OBJECTIVES

This study aims to assess the frequency and distribution of genetic parkinsonism in Latin America.

METHODS

We conducted a systematic review and meta-analysis of the frequency of parkinsonian syndromes associated with genetic pathogenic variants in Latin America. We defined hereditary parkinsonism as those caused by the genes outlined by the MDS Nomenclature of Genetic Movement Disorders and heterozygous carriers of GBA1 pathogenic variants. A systematic search was conducted in PubMed, Web of Science, Embase, and LILACS in August 2022. Researchers reviewed titles and abstracts, and disagreements were resolved by a third researcher. After this screening, five researchers reanalyzed the selection criteria and extracted information based on the full paper. The frequency for each parkinsonism-related gene was determined by the presence of pathogenic/likely pathogenic variants among screened patients. Cochran's Q and I2 tests were used to quantify heterogeneity. Meta-regression, publication bias tests, and sensitivity analysis regarding study quality were also used for LRRK2-, PRKN-, and GBA1-related papers.

RESULTS

We included 73 studies involving 3014 screened studies from 16 countries. Among 7668 Latin American patients, pathogenic variants were found in 19 different genes. The frequency of the pathogenic variants in LRRK2 was 1.38% (95% confidence interval [CI]: 0.52-2.57), PRKN was 1.16% (95% CI: 0.08-3.05), and GBA1 was 4.17% (95% CI: 2.57-6.08). For all meta-analysis, heterogeneity was high and publication bias tests were negative, except for PRKN, which was contradictory. Information on the number of pathogenic variants in the other genes is further presented in the text.

CONCLUSIONS

This study provides insights into hereditary and GBA1-related parkinsonism in Latin America. Lower GBA1 frequencies compared to European/North American cohorts may result from limited access to gene sequencing. Further research is vital for regional prevalence understanding, enabling personalized care and therapies. © 2023 The Authors. Movement Disorders published by Wiley Periodicals LLC on behalf of International Parkinson and Movement Disorder Society.

Pharmacology of Mammalian Na+-Dependent Transporters of Inorganic Phosphate

Inorganic phosphate (Pi) is an essential component of many biologically important molecules such as DNA, RNA, ATP, phospholipids, or apatite. It is required for intracellular phosphorylation signaling events and acts as pH buffer in intra- and extracellular compartments. Intestinal absorption, uptake into cells, and renal reabsorption depend on a set of different phosphate transporters from the SLC20 (PiT transporters) and SLC34 (NaPi transporters) gene families. The physiological relevance of these transporters is evident from rare monogenic disorders in humans affecting SLC20A2 (Fahr's disease, basal ganglia calcification), SLC34A1 (idiopathic infantile hypercalcemia), SLC34A2 (pulmonary alveolar microlithiasis), and SLC34A3 (hereditary hypophosphatemic rickets with hypercalciuria). SLC34 transporters are inhibited by millimolar concentrations of phosphonoformic acid or arsenate while SLC20 are relatively resistant to these compounds. More recently, a series of more specific and potent drugs have been developed to target SLC34A2 to reduce intestinal Pi absorption and to inhibit SLC34A1 and/or SLC34A3 to increase renal Pi excretion in patients with renal disease and incipient hyperphosphatemia. Also, SLC20 inhibitors have been developed with the same intention. Some of these substances are currently undergoing preclinical and clinical testing. Tenapanor, a non-absorbable Na+/H+-exchanger isoform 3 inhibitor, reduces intestinal Pi absorption likely by indirectly acting on the paracellular pathway for Pi and has been tested in several phase III trials for reducing Pi overload in patients with renal insufficiency and dialysis.

Fahr's disease linked to a novel mutation in MYORG variants manifesting as paroxysmal limb stiffness and dysarthria: Case report and literature review

BACKGROUND

Primary familial brain calcification (PFBC) is a rare hereditary neurodegenerative disorder associated with the MYORG gene; however, the clinical and radiological characteristics of MYORG-PFBC remain unclear.

METHODS

We present relevant medical data obtained from a patient affected by PFBC with a novel MYORG variant and conducted a mutational analysis of MYORG in her family members. We reviewed all reported PFBC cases with biallelic MYORG mutations until April 1, 2023, and summarized the associated clinical and radiological features and mutation sites.

RESULTS

The patient (22-year-old woman) exhibited paroxysmal limb stiffness and dysarthria for 3 years. Computed tomography revealed calcifications in the paraventricular white matter, basal ganglia, thalamus, and cerebellum. Whole-exome sequencing revealed a novel homozygous frameshift variant (c.743delG: p.G248Afs*32) in exon 2 of the MYORG gene (NM_020702.5). To date, 62 families and 64 mutation sites have been reported. Among the reported biallelic MYORG mutations, 57% were homozygous and 43% were compound heterozygous. Individuals with biallelic MYORG mutations experience more severe brain calcification with approximately 100% clinical penetrance. Ten single heterozygous mutation sites are associated with significant brain calcifications.

CONCLUSION

All patients with primary brain calcification, particularly younger patients without a family history of the disease, should be screened for MYORG mutations.

Inorganic phosphate exporter heterozygosity in mice leads to brain vascular calcification, microangiopathy, and microgliosis

Calcification of the cerebral microvessels in the basal ganglia in the absence of systemic calcium and phosphate imbalance is a hallmark of primary familial brain calcification (PFBC), a rare neurodegenerative disorder. Mutation in genes encoding for sodium-dependent phosphate transporter 2 (SLC20A2), xenotropic and polytropic retrovirus receptor 1 (XPR1), platelet-derived growth factor B (PDGFB), platelet-derived growth factor receptor beta (PDGFRB), myogenesis regulating glycosidase (MYORG), and junctional adhesion molecule 2 (JAM2) are known to cause PFBC. Loss-of-function mutations in XPR1, the only known inorganic phosphate exporter in metazoans, causing dominantly inherited PFBC was first reported in 2015 but until now no studies in the brain have addressed whether loss of one functional allele leads to pathological alterations in mice, a commonly used organism to model human diseases. Here we show that mice heterozygous for Xpr1 (Xpr1WT/lacZ ) present with reduced inorganic phosphate levels in the cerebrospinal fluid and age- and sex-dependent growth of vascular calcifications in the thalamus. Vascular calcifications are surrounded by vascular basement membrane and are located at arterioles in the smooth muscle layer. Similar to previously characterized PFBC mouse models, vascular calcifications in Xpr1WT/lacZ mice contain bone matrix proteins and are surrounded by reactive astrocytes and microglia. However, microglial activation is not confined to calcified vessels but shows a widespread presence. In addition to vascular calcifications, we observed vessel tortuosity and transmission electron microscopy analysis revealed microangiopathy-endothelial swelling, phenotypic alterations in vascular smooth muscle cells, and thickening of the basement membrane.

Mutations in human DNA methyltransferase DNMT1 induce specific genome-wide epigenomic and transcriptomic changes in neurodevelopment

DNA methyltransferase type 1 (DNMT1) is a major enzyme involved in maintaining the methylation pattern after DNA replication. Mutations in DNMT1 have been associated with autosomal dominant cerebellar ataxia, deafness and narcolepsy (ADCA-DN). We used fibroblasts, induced pluripotent stem cells (iPSCs) and induced neurons (iNs) generated from patients with ADCA-DN and controls, to explore the epigenomic and transcriptomic effects of mutations in DNMT1. We show cell type-specific changes in gene expression and DNA methylation patterns. DNA methylation and gene expression changes were negatively correlated in iPSCs and iNs. In addition, we identified a group of genes associated with clinical phenotypes of ADCA-DN, including PDGFB and PRDM8 for cerebellar ataxia, psychosis and dementia and NR2F1 for deafness and optic atrophy. Furthermore, ZFP57, which is required to maintain gene imprinting through DNA methylation during early development, was hypomethylated in promoters and exhibited upregulated expression in patients with ADCA-DN in both iPSC and iNs. Our results provide insight into the functions of DNMT1 and the molecular changes associated with ADCA-DN, with potential implications for genes associated with related phenotypes.

Generation and characterization of human induced pluripotent stem cell line METUi002-A from a patient with primary familial brain calcification (PFBC) carrying a heterozygous mutation (c.687dupT (p.Val230CysfsTer28)) in the SLC20A2 gene

Primary familial brain calcification (PFBC) is a rare neurological condition characterized by abnormal calcification commonly in basal ganglia and multiple other brain regions, leading to neuropsychiatric, cognitive, and motor symptoms. SLC20A2, one of the known causative genes for PFBC, contains the highest number of variants directly associated with the disease. Here, we established an iPSC line (METUi002-A) from the peripheral blood mononuclear cells of a clinically diagnosed PFBC patient carrying a SLC20A2 mutation (c.687dupT) using the integration-free Sendai reprogramming. METUi002-A can serve as a valuable tool to generate cellular models to investigate the mechanistic effects of this mutation in PFBC.

Homozygous SLC20A2 mutations cause congenital CMV infection-like phenotype

BACKGROUND

Idiopathic basal ganglia calcification, also known as Fahr's disease, it is a neurological disease characterized by intracranial calcification caused by heterozygous SLC20A2 mutations. Patients with calcifications can either be asymptomatic or show a wide spectrum of neuropsychiatric symptoms, including parkinsonism, tremor, dystonia, ataxia, and seizures.

OBJECTIVES

The aim of this study was to investigating the clinical implications of the SLCA20A2 gene and identifying a new phenotype through a family.

METHODS

Two siblings with growth retardation, bilateral cataracts, microcephaly, and convulsion were included in the study. The MRI showed cerebral atrophy, corpus callosum hypoplasia, microcalcifications. Chromosomal microarray analysis was performed to identify the existence of copy number variation. The whole exome sequencing analysis of the individual IV-I was performed, and Sanger sequencing was performed for segregation.

RESULTS

Whole exome sequencing revealed a homozygous NM_006749.5:c.1794 + 1G > A of the SLC20A2 gene. The Sanger sequencing confirmed the affected siblings were homozygous and the parents were heterozygous.

CONCLUSIONS

SLC20A2 gene heterozygous mutations were associated with the adult-onset phenotype, while homozygous SLC20A2 mutations in the two affected siblings we reported in our study resulted in a severe clinic including growth retardation, bilateral cataracts, microcephaly, and convulsion. We showed that biallelic mutations in the SLC20A2 gene that cause the Fahr's disease lead to more severe phenotypes contrary to what is known. The two siblings, showing similar phonotypic and genotypic characteristics, would be the youngest cases in the pediatric age group published in the literature.

The inhibition of mineralisation by fibroblast growth factor 2 is associated with the altered expression of genes regulating phosphate balance

The study aimed to determine whether inhibitory effects of fibroblast growth factor 2 (FGF2) on mineralisation in dental pulp (DP) cultures were associated with changes in the expression of genes regulating phosphate balance (Enpp1, Ank, Slc20a2, Alpl, Phospho1, and Xpr1). DP cultures growing under mineralisation-inducing conditions were exposed to FGF2 and inhibitors of the FGFR and MEK/ERK1/2 signaling pathways. Mineralisation, culture cellularity, and gene expression were examined at various time points. Statistical analysis was performed using analysis of variance followed by the Holm-Šídák test. Control cultures exhibited transient increases in Enpp1 and Ank, continuous increases in Alpl, Phospho1, and Xpr1, and continuous decreases in Slc20a2. FGF2 increased Enpp1, Ank, and Slc20a2 and decreased Alpl, Phospho1, and Xpr1, whereas the FGF2 withdrawal and inhibition of FGFR and MEK/ERK1/2 exerted opposite effects. These changes suggest that FGF2-mediated decreases in mineralisation could be functionally coupled to the altered regulation of phosphate formation and transport.

Transmembrane Transport of Inorganic Phosphate by a Strapped Calix[4]pyrrole

Synthetic anion receptors are increasingly being explored for the transport of anions across lipid membranes because of their potential therapeutic applications. A considerable amount of research focuses on the transport of chloride, whereas the transmembrane transport of inorganic phosphate has not been reported to date, despite the biological relevance of this anion. Here we present a calix[4]pyrrole with a bisurea strap that functions as a receptor and transporter for H₂PO₄^-, relying on the formation of eight hydrogen bonds and efficient encapsulation of the anion. Using a phosphate-sensitive lanthanide probe and ³¹P NMR spectroscopy, we demonstrate that this receptor can transport phosphate into vesicles by H₂PO₄^-/Cl^- antiport, H₂PO₄^- uniport, and Cs⁺/H₂PO₄^- symport mechanisms. This first example of inorganic phosphate transport by a neutral receptor opens perspectives for the future development of transporters for various biological phosphates.

The Genetics of Primary Familial Brain Calcification: A Literature Review

Primary familial brain calcification (PFBC), also known as Fahr's disease, is a rare inherited disorder characterized by bilateral calcification in the basal ganglia according to neuroimaging. Other brain regions, such as the thalamus, cerebellum, and subcortical white matter, can also be affected. Among the diverse clinical phenotypes, the most common manifestations are movement disorders, cognitive deficits, and psychiatric disturbances. Although patients with PFBC always exhibit brain calcification, nearly one-third of cases remain clinically asymptomatic. Due to advances in the genetics of PFBC, the diagnostic criteria of PFBC may need to be modified. Hitherto, seven genes have been associated with PFBC, including four dominant inherited genes (SLC20A2, PDGFRB, PDGFB, and XPR1) and three recessive inherited genes (MYORG, JAM2, and CMPK2). Nevertheless, around 50% of patients with PFBC do not have pathogenic variants in these genes, and further PFBC-associated genes are waiting to be identified. The function of currently known genes suggests that PFBC could be caused by the dysfunction of the neurovascular unit, the dysregulation of phosphate homeostasis, or mitochondrial dysfunction. An improved understanding of the underlying pathogenic mechanisms for PFBC may facilitate the development of novel therapies.

Medial Sclerosis-Epidemiology and Clinical Significance

BACKGROUND

Medial sclerosis (MeS) is a chronic systemic vascular disease that mainly affects the arteries of the lower limb. Its prevalence in the general population is approximately 2.5% (range: 1.6% to 10.0%). It is more common in men than in women.

METHODS

This review is based on pertinent publications retrieved by a selective search in PubMed.

RESULTS

MeS is the final common pathway of a wide variety of diseases; its pathogenesis is not fully understood. It often remains clinically silent for decades and is usually diagnosed as an incidental finding or in a late stage. MeS with or without atherosclerosis is the most common histologic finding after limb amputation. MeS of the below-the-knee arteries is a major risk factor for chronic critical leg ischemia (OR:13.25, 95% confidence interval: [1.69; 104.16]) and amputation (RR 2.27, [1.89; 2.74]). Patients with peripheral arterial occlusive disease and marked calcification have a much higher risk of amputation (OR 2.88, [1.18; 12.72]) and a higher mortality (OR 5.16, [1.13; 21.61]). MeS is a risk factor for the failure of endovascular treatment of the pedal arteries (OR 4.0, [1.1; 16.6]). The more marked the calcification, the higher the risk of major amputation (HR 10.6 [1.4; 80.7] to HR 15.5 [2.0; 119]). Patients with vascular calcifications have been found to have lower patency rates and higher treatment failure rates two years after open surgical revascularization of the below-the-knee arteries. No pharmacotherapy for MeS is available to date.

CONCLUSION

MeS is an important risk factor for chronic critical lower limb ischemia, amputation, morbidity, and complications, particularly after endovascular and surgical procedures.

Brain Calcifications: Genetic, Molecular, and Clinical Aspects

Many conditions can present with accumulation of calcium in the brain and manifest with a variety of neurological symptoms. Brain calcifications can be primary (idiopathic or genetic) or secondary to various pathological conditions (e.g., calcium-phosphate metabolism derangement, autoimmune disorders and infections, among others). A set of causative genes associated with primary familial brain calcification (PFBC) has now been identified, and include genes such as SLC20A2, PDGFB, PDGFRB, XPR1, MYORG, and JAM2. However, many more genes are known to be linked with complex syndromes characterized by brain calcifications and additional neurologic and systemic manifestations. Of note, many of these genes encode for proteins involved in cerebrovascular and blood-brain barrier functions, which both represent key anatomical structures related to these pathological phenomena. As a growing number of genes associated with brain calcifications is identified, pathways involved in these conditions are beginning to be understood. Our comprehensive review of the genetic, molecular, and clinical aspects of brain calcifications offers a framework for clinicians and researchers in the field.

Genomics of perivascular space burden unravels early mechanisms of cerebral small vessel disease

Perivascular space (PVS) burden is an emerging, poorly understood, magnetic resonance imaging marker of cerebral small vessel disease, a leading cause of stroke and dementia. Genome-wide association studies in up to 40,095 participants (18 population-based cohorts, 66.3 ± 8.6 yr, 96.9% European ancestry) revealed 24 genome-wide significant PVS risk loci, mainly in the white matter. These were associated with white matter PVS already in young adults (N = 1,748; 22.1 ± 2.3 yr) and were enriched in early-onset leukodystrophy genes and genes expressed in fetal brain endothelial cells, suggesting early-life mechanisms. In total, 53% of white matter PVS risk loci showed nominally significant associations (27% after multiple-testing correction) in a Japanese population-based cohort (N = 2,862; 68.3 ± 5.3 yr). Mendelian randomization supported causal associations of high blood pressure with basal ganglia and hippocampal PVS, and of basal ganglia PVS and hippocampal PVS with stroke, accounting for blood pressure. Our findings provide insight into the biology of PVS and cerebral small vessel disease, pointing to pathways involving extracellular matrix, membrane transport and developmental processes, and the potential for genetically informed prioritization of drug targets.

Role of transporters in regulating mammalian intracellular inorganic phosphate

This review summarizes the current understanding of the role of plasma membrane transporters in regulating intracellular inorganic phosphate ([Pi]In) in mammals. Pi influx is mediated by SLC34 and SLC20 Na+-Pi cotransporters. In non-epithelial cells other than erythrocytes, Pi influx via SLC20 transporters PiT1 and/or PiT2 is balanced by efflux through XPR1 (xenotropic and polytropic retrovirus receptor 1). Two new pathways for mammalian Pi transport regulation have been described recently: 1) in the presence of adequate Pi, cells continuously internalize and degrade PiT1. Pi starvation causes recycling of PiT1 from early endosomes to the plasma membrane and thereby increases the capacity for Pi influx; and 2) binding of inositol pyrophosphate InsP8 to the SPX domain of XPR1 increases Pi efflux. InsP8 is degraded by a phosphatase that is strongly inhibited by Pi. Therefore, an increase in [Pi]In decreases InsP8 degradation, increases InsP8 binding to SPX, and increases Pi efflux, completing a feedback loop for [Pi]In homeostasis. Published data on [Pi]In by magnetic resonance spectroscopy indicate that the steady state [Pi]In of skeletal muscle, heart, and brain is normally in the range of 1–5 mM, but it is not yet known whether PiT1 recycling or XPR1 activation by InsP8 contributes to Pi homeostasis in these organs. Data on [Pi]In in cultured cells are variable and suggest that some cells can regulate [Pi] better than others, following a change in [Pi]Ex. More measurements of [Pi]In, influx, and efflux are needed to determine how closely, and how rapidly, mammalian [Pi]In is regulated during either hyper- or hypophosphatemia.

The clinical and genetic spectrum of primary familial brain calcification

Primary familial brain calcification (PFBC), formerly known as Fahr's disease, is a rare neurodegenerative disease characterized by bilateral progressive calcification of the microvessels of the basal ganglia and other cerebral and cerebellar structures. PFBC is thought to be due to an altered function of the Neurovascular Unit (NVU), where abnormal calcium-phosphorus metabolism, functional and microanatomical alterations of pericytes and mitochondrial alterations cause a dysfunction of the blood-brain barrier (BBB) and the generation of an osteogenic environment with surrounding astrocyte activation and progressive neurodegeneration. Seven causative genes have been discovered so far, of which four with dominant (SLC20A2, PDGFB, PDGFRB, XPR1) and three with recessive inheritance (MYORG, JAM2, CMPK2). Clinical presentation ranges from asymptomatic subjects to movement disorders, cognitive decline and psychiatric disturbances alone or in various combinations. Radiological patterns of calcium deposition are similar in all known genetic forms, but central pontine calcification and cerebellar atrophy are highly suggestive of MYORG mutations and extensive cortical calcification has been associated with JAM2 mutations. Currently, no disease-modifying drugs or calcium-chelating agents are available and only symptomatic treatments can be offered.

Aneurysmal subarachnoid hemorrhage with PFBC and beta thalassemia: a case report

BACKGROUND

Primary familial brain calcification (PFBC), habitually called Fahr's disease, is characterized by bilateral calcification of the basal ganglia, accompanied by extensive calcification of the cerebellar dentate nucleus, brainstem cerebrum, and cerebellum at the grey-white matter junction. However, there are few reports about PFBC with aneurysmal subarachnoid hemorrhage (aSAH) and thalassemia.

CASE PRESENTATION

We describe a patient admitted to the hospital with an acute deterioration in the level of consciousness with no history of neuropsychiatric features or movement disorders. After computed tomography (CT) and CT angiography (CTA), the patient was diagnosed with PFBC, accompanied by aneurysmal subarachnoid haemorrhage (aSAH), intracranial haemorrhage (ICH), and hemoglobin electrophoresis suggested beta-thalassemia. This patient underwent craniotomy aneurysm clipping and intracranial hematoma removal.

CONCLUSIONS

For patients with PFBC, we should pay attention to their blood pressure and intracranial vascular conditions. The CTA is necessary to clarify the cerebrovascular conditions of the patient, especially when combined with hypertension and persistent headache or other related prodromal symptoms of cerebrovascular disease.

T-cell infiltration in the central nervous system and their association with brain calcification in Slc20a2-deficient mice

Primary familial brain calcification (PFBC) is a rare neurodegenerative and neuropsychiatric disorder characterized by bilateral symmetric intracranial calcification along the microvessels or inside neuronal cells in the basal ganglia, thalamus, and cerebellum. Slc20a2 homozygous (HO) knockout mice are the most commonly used model to simulate the brain calcification phenotype observed in human patients. However, the cellular and molecular mechanisms related to brain calcification, particularly at the early stage much prior to the emergence of brain calcification, remain largely unknown. In this study, we quantified the central nervous system (CNS)-infiltrating T-cells of different age groups of Slc20a2-HO and matched wild type mice and found CD45⁺CD3⁺ T-cells to be significantly increased in the brain parenchyma, even in the pre-calcification stage of 1-month-old -HO mice. The accumulation of the CD3⁺ T-cells appeared to be associated with the severity of brain calcification. Further immunophenotyping revealed that the two main subtypes that had increased in the brain were CD3⁺ CD4^- CD8^- and CD3⁺ CD4⁺ T-cells. The expression of endothelial cell (EC) adhesion molecules increased, while that of tight and adherents junction proteins decreased, providing the molecular precondition for T-cell recruitment to ECs and paracellular migration into the brain. The fusion of lymphocytes and EC membranes and transcellular migration of CD3-related gold particles were captured, suggesting enhancement of transcytosis in the brain ECs. Exogenous fluorescent tracers and endogenous IgG and albumin leakage also revealed an impairment of transcellular pathway in the ECs. FTY720 significantly alleviated brain calcification, probably by reducing T-cell infiltration, modulating neuroinflammation and ossification process, and enhancing the autophagy and phagocytosis of CNS-resident immune cells. This study clearly demonstrated CNS-infiltrating T-cells to be associated with the progression of brain calcification. Impairment of blood-brain barrier (BBB) permeability, which was closely related to T-cell invasion into the CNS, could be explained by the BBB alterations of an increase in the paracellular and transcellular pathways of brain ECs. FTY720 was found to be a potential drug to protect patients from PFBC-related lesions in the future.

Role of phosphate transporter PiT-2 in the pathogenesis of primary brain calcification

Primary brain calcification (PBC), also known as idiopathic basal ganglia calcification (IBGC), primary familial brain calcification (PFBC) and so on, is a rare intractable disease characterized by abnormal mineral deposits, including mostly calcium in the basal ganglia, thalamus, and cerebellum. The causative gene of familial PBC is SLC20A2, which encodes the phosphate transporter PiT-2. Despite this knowledge, the molecular mechanism underlying SLC20A2-associated PBC remains unclear. In the present study, we investigated whether haploinsufficiency or a dominant-negative mechanism reduced Pi uptake in two PiT-2 variants (T115 M and R467X). We demonstrated that the presence of T115 M or R467X had no dominant-negative effect on Pi transport activity of wild-type (WT). In addition, the subcellular localization of R467X completely differed from that of WT, indicating that there is no interaction between R467X and WT. Conversely, T115 M and WT showed almost the same localization. Therefore, we examined the interaction between T115 M and WT using the bioluminescence resonance energy transfer (BRET) method. Although WT and T115 M interact with each other, T115 M does not inhibit WT's Pi transport activity. These results suggest that the role of SLC20A2 in the pathogenesis of PBC may involve decreased intracellular Pi uptake by a haploinsufficiency mechanism rather than a dominant-negative mechanism; agents promoting PiT-2 dimerization may be promising potential therapeutic agents for PBC.

Mechanisms of PiT2-loop7 Missense Mutations Induced Pi Dyshomeostasis

PiT2 is an inorganic phosphate (Pi) transporter whose mutations are linked to primary familial brain calcification (PFBC). PiT2 mainly consists of two ProDom (PD) domains and a large intracellular loop region (loop7). The PD domains are crucial for the Pi transport, but the role of PiT2-loop7 remains unclear. In PFBC patients, mutations in PiT2-loop7 are mainly nonsense or frameshift mutations that probably cause PFBC due to C-PD1131 deletion. To date, six missense mutations have been identified in PiT2-loop7; however, the mechanisms by which these mutations cause PFBC are poorly understood. Here, we found that the p.T390A and p.S434W mutations in PiT2-loop7 decreased the Pi transport activity and cell surface levels of PiT2. Furthermore, we showed that these two mutations attenuated its membrane localization by affecting adenosine monophosphate-activated protein kinase (AMPK)- or protein kinase B (AKT)-mediated PiT2 phosphorylation. In contrast, the p.S121C and p.S601W mutations in the PD domains did not affect PiT2 phosphorylation but rather impaired its substrate-binding abilities. These results suggested that missense mutations in PiT2-loop7 can cause Pi dyshomeostasis by affecting the phosphorylation-regulated cell-surface localization of PiT2. This study helps understand the pathogenesis of PFBC caused by PiT2-loop7 missense mutations and indicates that increasing the phosphorylation levels of PiT2-loop7 could be a promising strategy for developing PFBC therapies.

The Pathology of Primary Familial Brain Calcification: Implications for Treatment

Primary familial brain calcification (PFBC) is an inherited neurodegenerative disorder mainly characterized by progressive calcium deposition bilaterally in the brain, accompanied by various symptoms, such as dystonia, ataxia, parkinsonism, dementia, depression, headaches, and epilepsy. Currently, the etiology of PFBC is largely unknown, and no specific prevention or treatment is available. During the past 10 years, six causative genes (SLC20A2, PDGFRB, PDGFB, XPR1, MYORG, and JAM2) have been identified in PFBC. In this review, considering mechanistic studies of these genes at the cellular level and in animals, we summarize the pathogenesis and potential preventive and therapeutic strategies for PFBC patients. Our systematic analysis suggests a classification for PFBC genetic etiology based on several characteristics, provides a summary of the known composition of brain calcification, and identifies some potential therapeutic targets for PFBC.

Knockdown of myorg leads to brain calcification in zebrafish

Primary familial brain calcification (PFBC) is a neurogenetic disorder characterized by bilateral calcified deposits in the brain. We previously identified that MYORG as the first pathogenic gene for autosomal recessive PFBC, and established a Myorg-KO mouse model. However, Myorg-KO mice developed brain calcifications until nine months of age, which limits their utility as a facile PFBC model system. Hence, whether there is another typical animal model for mimicking PFBC phenotypes in an early stage still remained unknown. In this study, we profiled the mRNA expression pattern of myorg in zebrafish, and used a morpholino-mediated blocking strategy to knockdown myorg mRNA at splicing and translation initiation levels. We observed multiple calcifications throughout the brain by calcein staining at 2–4 days post-fertilization in myorg-deficient zebrafish, and rescued the calcification phenotype by replenishing myorg cDNA. Overall, we built a novel model for PFBC via knockdown of myorg by antisense oligonucleotides in zebrafish, which could shorten the observation period and replenish the Myorg-KO mouse model phenotype in mechanistic and therapeutic studies.

Loss of function of CMPK2 causes mitochondria deficiency and brain calcification

Brain calcification is a critical aging-associated pathology and can cause multifaceted neurological symptoms. Cerebral phosphate homeostasis dysregulation, blood-brain barrier defects, and immune dysregulation have been implicated as major pathological processes in familial brain calcification (FBC). Here, we analyzed two brain calcification families and identified calcification co-segregated biallelic variants in the CMPK2 gene that disrupt mitochondrial functions. Transcriptome analysis of peripheral blood mononuclear cells (PBMCs) isolated from these patients showed impaired mitochondria-associated metabolism pathways. In situ hybridization and single-cell RNA sequencing revealed robust Cmpk2 expression in neurons and vascular endothelial cells (vECs), two cell types with high energy expenditure in the brain. The neurons in Cmpk2-knockout (KO) mice have fewer mitochondrial DNA copies, down-regulated mitochondrial proteins, reduced ATP production, and elevated intracellular inorganic phosphate (Pi) level, recapitulating the mitochondrial dysfunction observed in the PBMCs isolated from the FBC patients. Morphologically, the cristae architecture of the Cmpk2-KO murine neurons was also impaired. Notably, calcification developed in a progressive manner in the homozygous Cmpk2-KO mice thalamus region as well as in the Cmpk2-knock-in mice bearing the patient mutation, thus phenocopying the calcification pathology observed in the patients. Together, our study identifies biallelic variants of CMPK2 as novel genetic factors for FBC; and demonstrates how CMPK2 deficiency alters mitochondrial structures and functions, thereby highlighting the mitochondria dysregulation as a critical pathogenic mechanism underlying brain calcification.

SLC20A2-Associated Idiopathic basal ganglia calcification (Fahr disease): a case family report

Background

Idiopathic basal ganglia calcification (IBGC) is a genetic disorder of the nervous system commonly known as Fahr disease. IBGC patients with a genetic background are considered to have primary familial brain calcification (PFBC), also known as familial basal ganglia calcification (FBGC), or familial Fahr disease. It is a rare degenerative neurological disorder characterized by extensive bilateral basal ganglia calcification that can lead to a range of extrapyramidal symptoms and neuropsychiatric manifestations. Studies have suggested that more than 50 variants of SLC20A2 gene mutations account for approximately 50% of IBGC cases. There is a wide spectrum of mutation types, including frameshift, nonsense, and splice site mutations in addition to deletion and missense mutations. Here we report a case of familial basal ganglia calcification caused by a frameshift mutation in the SLC20A2 gene. We identified a heterozygous mutation in the SLC20A2 gene, c.1097delG (p.G366fs*89). To our knowledge, this mutation site has not been reported before.

Case presentation

A 57-year-old male patient was admitted to the hospital with “unstable walking and involuntary movements between the eyes and eyebrows for 6 months”. Based on the patient’s family history, symmetrical calcification foci in the bilateral caudate nucleus head, thalamus, cerebellum and parietal lobe indicated by head CT, and gene test results, the diagnosis of familial Fahr disease caused by mutations in the SLC20A2 gene, c.1097delG p.G366fs*89) was confirmed.

Conclusion

For the first time, we identified c.1097delG (p.G366fs*89) as a frameshift mutation in the IBGC family. This frameshift mutation caused the condition in this family of patients. This mutation not only broadens the range of known SLC20A2 mutations but also aids in the genetic diagnosis of IBGC.

Medical care of rare and undiagnosed diseases: Prospects and challenges

Rare and undiagnosed diseases tend to be diverse, misdiagnosed, and difficult to diagnose. In some cases, the disease is progressive and life-threatening. Yet, to date, an estimated 95% of rare diseases have no approved therapy. Therefore, rare and undiagnosed diseases are considered the ultimate challenges for understanding human diseases. Here, we review the research progress, research frontiers, and important scientific issues related to rare and undiagnosed diseases. We mainly focus on five topics: (1) the identification and functional analysis of disease-causing genes; (2) the construction of cells, organoids, and animal models for mechanism validation; (3) subtyping and diagnosis; (4) treatment and drug screening based on causative genes and mutations; and (5) new technologies and methods for studying rare and undiagnosed diseases. In this review, we briefly update and discuss the pathogenic mechanisms and precision medicine for rare and undiagnosed diseases.

Microglia shield the murine brain from damage mediated by the cytokines IL-6 and IFN-α

Sustained production of elevated levels of the cytokines interleukin (IL)-6 or interferon (IFN)-α in the central nervous system (CNS) is detrimental and directly contributes to the pathogenesis of neurological diseases such as neuromyelitis optica spectrum disorders or cerebral interferonopathies, respectively. Using transgenic mice with CNS-targeted production of IL-6 (GFAP-IL6) or IFN-α (GFAP-IFN), we have recently demonstrated that microglia are prominent target and effector cells and mount stimulus-specific responses to these cytokines. In order to further clarify the phenotype and function of these cells, we treated GFAP-IL6 and GFAP-IFN mice with the CSF1R inhibitor PLX5622 to deplete microglia. We examined their ability to recover from acute microglia depletion, as well as the impact of chronic microglia depletion on the progression of disease. Following acute depletion in the brains of GFAP-IL6 mice, microglia repopulation was enhanced, while in GFAP-IFN mice, microglia did not repopulate the brain. Furthermore, chronic CSF1R inhibition was detrimental to the brain of GFAP-IL6 and GFAP-IFN mice and gave rise to severe CNS calcification which strongly correlated with the absence of microglia. In addition, PLX5622-treated GFAP-IFN mice had markedly reduced survival. Our findings provide evidence for novel microglia functions to protect against IFN-α-mediated neurotoxicity and neuronal dysregulation, as well as restrain calcification as a result of both IL-6- and IFN-α-induced neuroinflammation. Taken together, we demonstrate that CSF1R inhibition may be an undesirable target for therapeutic treatment of neuroinflammatory diseases that are driven by elevated IL-6 and IFN-α production.

Living with primary brain calcification with PDGFB variants: A qualitative study

Introduction

Primary brain calcification (PBC) is a rare and intractable neurodegenerative disease. SLC20A2 and PDGFB are two major causative genes. As there is no effective treatment to avoid further progression or to prevent the onset of the disease, the patients may experience psychological distress. There is a qualitative study on the experiences of patients with primary brain calcification with SLC20A2 variants. However, the experiences of patients with PDGFB variants of the disease have not been explored. The purpose of this study is to identify the experiences of patients with PDGFB variants after diagnosis.

Materials and methods

Semi-structured interviews were conducted once or twice a year for three years with five patients over the age of 21. The data were analyzed using inductive qualitative methods.

Results

Seven categories, 15 subcategories, and 129 codes were extracted. The seven categories are as follows: [Shock at hearing the term ‘brain calcification’ for the first time], [Anxiety regarding the risk of heredity], [Anxiety, along with severe headaches, and various other symptoms], [Gratitude for the family members who care], [Accepting the disease as a non-life-threatening illness], [Feeling alienated due to the rare intractable disease], and [Modifying lifestyle due to the illness].

Discussion

The most stressful aspect of the disease was the headache that persisted even with the use of analgesics, which was different from patients with the SLC20A2 variants. In addition, we found unique concepts such as anxiety regarding the risk of heredity and a feeling of alienation due to the rare and intractable disease.

The primary familial brain calcification-associated protein MYORG is an α-galactosidase with restricted substrate specificity

Primary familial brain calcification (PFBC) is characterised by abnormal deposits of calcium phosphate within various regions of the brain that are associated with severe cognitive impairments, psychiatric conditions, and movement disorders. Recent studies in diverse populations have shown a link between mutations in myogenesis-regulating glycosidase (MYORG) and the development of this disease. MYORG is a member of glycoside hydrolase (GH) family 31 (GH31) and, like the other mammalian GH31 enzyme α-glucosidase II, this enzyme is found in the lumen of the endoplasmic reticulum (ER). Though presumed to act as an α-glucosidase due to its localization and sequence relatedness to α-glucosidase II, MYORG has never been shown to exhibit catalytic activity. Here, we show that MYORG is an α-galactosidase and present the high-resolution crystal structure of MYORG in complex with substrate and inhibitor. Using these structures, we map detrimental mutations that are associated with MYORG-associated brain calcification and define how these mutations may drive disease progression through loss of enzymatic activity. Finally, we also detail the thermal stabilisation of MYORG afforded by a clinically approved small molecule ligand, opening the possibility of using pharmacological chaperones to enhance the activity of mutant forms of MYORG.

MYORG is an enzyme genetically linked to primary familial brain calcification that has historically been presumed to act as an α-glucosidase. This study describes the crystal structure of dimeric MYORG and, surprisingly, reveals it to be an α-galactosidase with restricted specificity.