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.

Case report: Novel insights into hemorrhagic destruction of the brain, subependymal calcification, and cataracts disease

Introduction

Pathogenic variants of the junctional adhesion molecule 3 (JAM3/JAM-C; OMIM#606871) is the cause of the rare recessive disorder called hemorrhagic destruction of the brain, subependymal calcification, and cataracts (HDBSCC, OMIM#613730) disease. A similar phenotype is universal, including congenital cataracts and brain hemorrhages with high mortality rate in the first few weeks of life and with a poor neurologic outcome in survivors. We aim to describe and enlighten novel phenotype and genotype of a new patient and review the literature regarding all reported patients worldwide.

Case report

We report the case of a prenatal and postnatal phenotype of a new patient with a novel pathogenic loss-of-function variant in JAM3, who presented prenatally with cataracts and brain anomalies and postnatally with brain hemorrhages, failure to thrive (FTT), progressive microcephaly, recurrent posterior capsule opacities, and auditory neuropathy.

Discussion

This study enlightens novel possible functions of JAM3 in the normal development of the brain, the ocular lenses, the auditory system, and possibly the gastrointestinal tract. This study is the first to report of cataracts evident in as early as 23 weeks of gestation and a rare phenomenon of recurrent posterior capsule opacities despite performing recurrent posterior capsulectomy and anterior vitrectomy. We suggest that auditory neuropathy, which is reported here for the first time, is part of the phenotype of HDBSCC, probably due to an endothelial microvasculature disruption of the peripheral eighth nerve or possibly due to impaired nerve conduction from the synapse to the brainstem.

Conclusions

Prenatal cataracts, brain anomalies, FTT, and auditory neuropathy are part of the phenotype of the HDBSCC disease. We suggest including JAM3 in the gene list known to cause congenital cataracts, brain hemorrhages, and hearing loss. Further studies should address the auditory neuropathy and FTT phenomena in knockout mice models. We further suggest performing comprehensive ophthalmic, audiologic, and gastroenterologic evaluations for living patients worldwide to further confirm these novel phenomena in this rare entity.

Case report: Mitochondrial trifunctional protein deficiency caused by HADHB gene mutation (c.1175C>T) characterized by higher brain dysfunction followed by neuropathy, presented gadolinium enhancement on brain imaging in an adult patient

Mitochondrial trifunctional protein (MTP) deficiency is an autosomal recessive disorder caused by impaired metabolism of long-chain fatty acids (LCFAs). Childhood and late-onset MTP deficiency is characterized by myopathy/rhabdomyolysis and peripheral neuropathy; however, the features are unclear. A 44-year-old woman was clinically diagnosed with Charcot-Marie-Tooth disease at 3 years of age due to gait disturbance. Her activity and voluntary speech gradually decreased in her 40s. Cognitive function was evaluated and brain imaging tests were performed. The Mini-Mental State Examination and frontal assessment battery scores were 25/30 and 10/18, respectively, suggesting higher brain dysfunction. Peripheral nerve conduction studies revealed axonal impairments. Brain computed tomography showed significant calcification. Magnetic resonance imaging revealed an increased gadolinium contrast-enhanced signal in the white matter, suggesting demyelination of the central nervous system (CNS) due to LCFAs. The diagnosis of MTP deficiency was confirmed through genetic examination. Administration of L-carnitine and a medium-chain fatty triglyceride diet was initiated, and the progression of higher brain dysfunction was retarded within 1 year. This patient's presentation was suggestive of CNS demyelination. The presence of brain calcification, higher brain dysfunction, or gadolinium enhancement in the white matter in patients with peripheral neuropathy may be suggestive of MTP deficiency.

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.

Absence of microglia promotes diverse pathologies and early lethality in Alzheimer's disease mice

Microglia are strongly implicated in the development and progression of Alzheimer's disease (AD), yet their impact on pathology and lifespan remains unclear. Here we utilize a CSF1R hypomorphic mouse to generate a model of AD that genetically lacks microglia. The resulting microglial-deficient mice exhibit a profound shift from parenchymal amyloid plaques to cerebral amyloid angiopathy (CAA), which is accompanied by numerous transcriptional changes, greatly increased brain calcification and hemorrhages, and premature lethality. Remarkably, a single injection of wild-type microglia into adult mice repopulates the microglial niche and prevents each of these pathological changes. Taken together, these results indicate the protective functions of microglia in reducing CAA, blood-brain barrier dysfunction, and brain calcification. To further understand the clinical implications of these findings, human AD tissue and iPSC-microglia were examined, providing evidence that microglia phagocytose calcium crystals, and this process is impaired by loss of the AD risk gene, TREM2.

Fahr's Syndrome Presenting With Hypocalcemia and Psychotic Features

Fahr's disease is a rare genetic neurodegenerative disorder described as “bilateral striopallidodentate calcinosis” (BSPDC). It is characterized by calcium deposition crossing the blood-brain barrier and calcifying different brain areas. Here, we report a case of a 26-year-old Saudi young lady, known as a case of epilepsy since childhood, a major depressive disorder with psychotic features, and hypocalcemia related to hypoparathyroidism. CT brain showed extensive coarse calcifications involving the infra and supratentorial white matter, predominantly within the basal ganglia, thalami, and dentate nuclei of cerebellar hemispheres. This report will discuss the challenging presentation, clinical symptoms, and the multidisciplinary approach to manage Fahr's syndrome symptoms. In conclusion, this case emphasizes the importance of neuroimaging and metabolic workup when investigating the seizure's etiology. The goal of treatment in Fahr's syndrome is to manage the underlying conditions.

Multisystem inflammation and susceptibility to viral infections in human ZNFX1 deficiency

BACKGROUND

Recognition of viral nucleic acids is one of the primary triggers for a type I interferon-mediated antiviral immune response. Inborn errors of type I interferon immunity can be associated with increased inflammation and/or increased susceptibility to viral infections as a result of dysbalanced interferon production. NFX1-type zinc finger-containing 1 (ZNFX1) is an interferon-stimulated double-stranded RNA sensor that restricts the replication of RNA viruses in mice. The role of ZNFX1 in the human immune response is not known.

OBJECTIVE

We studied 15 patients from 8 families with an autosomal recessive immunodeficiency characterized by severe infections by both RNA and DNA viruses and virally triggered inflammatory episodes with hemophagocytic lymphohistiocytosis-like disease, early-onset seizures, and renal and lung disease.

METHODS

Whole exome sequencing was performed on 13 patients from 8 families. We investigated the transcriptome, posttranscriptional regulation of interferon-stimulated genes (ISGs) and predisposition to viral infections in primary cells from patients and controls stimulated with synthetic double-stranded nucleic acids.

RESULTS

Deleterious homozygous and compound heterozygous ZNFX1 variants were identified in all 13 patients. Stimulation of patient-derived primary cells with synthetic double-stranded nucleic acids was associated with a deregulated pattern of expression of ISGs and alterations in the half-life of the mRNA of ISGs and also associated with poorer clearance of viral infections by monocytes.

CONCLUSION

ZNFX1 is an important regulator of the response to double-stranded nucleic acids stimuli following viral infections. ZNFX1 deficiency predisposes to severe viral infections and a multisystem inflammatory disease.

Astrocyte-microglial association and matrix composition are common events in the natural history of primary familial brain calcification

Primary familial brain calcification (PFBC) is an age-dependent and rare neurodegenerative disorder characterized by microvascular calcium phosphate deposits in the deep brain regions. Known genetic causes of PFBC include loss-of-function mutations in genes involved in either of three processes-platelet-derived growth factor (PDGF) signaling, phosphate homeostasis or protein glycosylation-with unclear molecular links. To provide insight into the pathogenesis of PFBC, we analyzed murine models of PFBC for the first two of these processes in Pdgfb^ret/ret and Slc20a2^-/- mice with regard to the structure, molecular composition, development and distribution of perivascular calcified nodules. Analyses by transmission electron microscopy and immunofluorescence revealed that calcified nodules in both of these models have a multilayered ultrastructure and occur in direct contact with reactive astrocytes and microglia. However, whereas nodules in Pdgfb^ret/ret mice were large, solitary and smooth surfaced, the nodules in Slc20a2^-/- mice were multi-lobulated and occurred in clusters. The regional distribution of nodules also differed between the two models. Proteomic analysis and immunofluorescence stainings revealed a common molecular composition of the nodules in the two models, involving proteins implicated in bone homeostasis, but also proteins not previously linked to tissue mineralization. While the brain vasculature of Pdgfb^ret/ret mice has been reported to display reduced pericyte coverage and abnormal permeability, we found that Slc20a2^-/- mice have a normal pericyte coverage and no overtly increased permeability. Thus, lack of pericytes and increase in permeability of the blood-brain barrier are likely not the causal triggers for PFBC pathogenesis. Instead, gene expression and spatial correlations suggest that astrocytes are intimately linked to the calcification process in PFBC.

Assessment of Physiological Intracranial Calcification in Healthy Adults Using 18F-NaF PET/CT

The aim of this research study was to determine the role of 18F-Sodium fluoride (NaF) PET/CT imaging in the assessment of physiologic molecular calcification in the intra-cranial structures. We also examined the association of NaF accumulation with age as well as Hounsfield unit (HU) in certain anatomical sites that are known to calcify with normal aging. Methods: A total of 78 healthy subjects from the Cardiovascular Molecular Calcification Assessed by 18F-NaF PET/CT (CAMONA) clinical trial (38 females and 40 males) were included in this retrospective study. The mean age was 45.28 ±14.15 years (21-75). Mean standardized uptake values (SUVmean) was used to measure NaF accumulation in the choroid plexus and epithalamus (pineal gland and habenula). Maximum HU was also measured for each ROI. Correlation analysis was conducted to assess the association between parameters. Results: Mean SUVmean was 0.42 ± 0.26 in the right choroid plexus, 0.39 ±25 in the left choroid plexus, and 0.23±0.08 in the epithalamus. Significant positive correlations were present between NaF uptake and age in the right choroid plexus (r=0.61, P < 0.0001), left choroid plexus (r=0.63, p<0.0001), and epithalamus (r=0.36, P = 0.001). NaF uptake significantly correlated with HU in the right choroid plexus (r=0.52, P < 0.0001), left choroid plexus (r=0.57, p<0.0001), and epithalamus (r=0.25, P = 0.03). Conclusion: NaF could be used in the assessment of physiological calcification in several intracranial structures. We report significant associations between NaF uptake and aging as well as HU in the calcified choroid plexus and epithalamus. Our findings further support the growing interest to utilize NaF for detecting extra-osseous, molecular calcification, and this powerful probe has potential applications in the evaluation of various age-related, neurodegenerative brain processes.

Biallelic Mutations in MYORG Cause Autosomal Recessive Primary Familial Brain Calcification

Primary familial brain calcification (PFBC) is a genetically heterogeneous disorder characterized by bilateral calcifications in the basal ganglia and other brain regions. The genetic basis of this disorder remains unknown in a significant portion of familial cases. Here, we reported a recessive causal gene, MYORG, for PFBC. Compound heterozygous or homozygous mutations of MYORG co-segregated completely with PFBC in six families, with logarithm of odds (LOD) score of 4.91 at the zero recombination fraction. In mice, Myorg mRNA was expressed specifically in S100β-positive astrocytes, and knockout of Myorg induced the formation of brain calcification at 9 months of age. Our findings provide strong evidence that loss-of-function mutations of MYORG cause brain calcification in humans and mice.

Autosomal-dominant early-onset spastic paraparesis with brain calcification due to IFIH1 gain-of-function

We describe progressive spastic paraparesis in two male siblings and the daughter of one of these individuals. Onset of disease occurred within the first decade, with stiffness and gait difficulties. Brisk deep tendon reflexes and extensor plantar responses were present, in the absence of intellectual disability or dermatological manifestations. Cerebral imaging identified intracranial calcification in all symptomatic family members. A marked upregulation of interferon-stimulated gene transcripts was recorded in all three affected individuals and in two clinically unaffected relatives. A heterozygous IFIH1 c.2544T>G missense variant (p.Asp848Glu) segregated with interferon status. Although not highly conserved (CADD score 10.08 vs. MSC-CADD score of 19.33) and predicted as benign by in silico algorithms, this variant is not present on publically available databases of control alleles, and expression of the D848E construct in HEK293T cells indicated that it confers a gain-of-function. This report illustrates, for the first time, the occurrence of autosomal-dominant spastic paraplegia with intracranial calcifications due to an IFIH1-related type 1 interferonopathy.

The role of the dorsal Anterior Cingulate Cortex (dACC) in a cognitive and emotional counting Stroop task: Two cases

BACKGROUND

The anterior cingulate cortex (ACC) has been implicated in both cognitive and emotional processing, with cognitive information proposed to be processed through the dorsal/caudal ACC and emotional information through the rostral/ventral ACC.

OBJECTIVE

The objective of this study is to investigate the role of the dorsal anterior cingulate cortex (dACC) in cognitive and emotional processing using a cognitive and emotional counting Stroop task in two patients in whom abnormalities in the dACC were identified and treated.

METHODS

Two patients performed the cognitive and emotional counting Stroop task before and after treatment to examine whether the dACC has a specific or more general processing function.

RESULTS

We observed an overall improvement in the emotional, cognitive, and neutral trials of the counting Stroop task after the intervention, indicating that the dACC is not a subregion of the ACC that only contributes to a specific domain.

CONCLUSION

This study reveals that the dACC is not just a subregion of the ACC that contributes to a specific cognitive function, but is rather part of a salience network that influences general brain functioning, influencing cognitive as well as emotional processing.

New Data from Pdfgb ret/ret Mutant Mice Might Lead to a Paradoxical Association Between Brain Calcification, Pericytes Recruitment and BBB Integrity

Data of mice with PDGF-B-truncating mutation (Pdgfb ^ret/ret) from different research groups indicate that the malfunction of this protein leads to reduced pericyte recruitment, loss of Blood-Brain Barrier (BBB) integrity and bilateral brain calcification. This makes these mice important models for Primary Brain Calcification and pericyte-BBB correlation studies. The global brain pericyte count is reduced in Pdgfb ^ret/ret mice, with higher BBB permeability. We have overlapped the data from other research groups into a figure to further analyze the findings. Calcifications form within midbrain, interbrain, basal forebrain, and pons. Interestingly, these calcification-prone regions have a comparably higher pericyte count and lower BBB leakage in relation to other non-calcifying regions of the Pdgfb ^ret/ret mouse (such as the cortex and striatum). A comparatively higher BBB integrity in regions prone to calcification seems paradoxical and indicates that other region-specific changes are the cause of the calcifications.

Primary familial brain calcification with a novel SLC20A2 mutation: Analysis of PiT-2 expression and localization

Primary familial brain calcification (PFBC) is an autosomal dominant rare disorder characterized by bilateral and symmetric brain calcifications, and neuropsychiatric manifestations. Four genes have been linked to PFBC: SLC20A2, PDGFRB, PDGFB, and XPR1. In this study, we report molecular and clinical data of a PFBC patient carrying a novel SLC20A2 mutation and we investigate the impact of the mutation on PiT-2 expression and function. Sanger sequencing of SLC20A2, PDGFRB, PDGFB, XPR1 led to the identification of a novel duplication of twelve nucleotides (c.1876_1887dup/ p.Trp626_Thr629dup) in SLC20A2 gene. SLC20A2 encodes for a cell membrane transporter (PiT-2) involved in maintenance of inorganic phosphate homeostasis. We performed an analysis of expression and functionality of PiT-2 protein in patient primary cultured fibroblasts. In patient fibroblasts, the mutation does not affect PiT-2 expression but alter sub-cellular localization. The Pi-uptake assay revealed a less Pi depletion in patient than in control fibroblasts, suggesting that SLC20A2 duplication may impair Pi internalization. This is the first study reporting sub-cellular expression analysis of mutant PiT-2 in primary cultured fibroblasts from a PFBC patient, showing that p.Trp626_Thr629dup in SLC20A2 alters PiT-2 sub-cellular localization and reduces Pi-uptake, leading to onset of PFBC in our patient.

Update and Mutational Analysis of SLC20A2: A Major Cause of Primary Familial Brain Calcification

Primary familial brain calcification (PFBC) is a heterogeneous neuropsychiatric disorder, with affected individuals presenting a wide variety of motor and cognitive impairments, such as migraine, parkinsonism, psychosis, dementia, and mood swings. Calcifications are usually symmetrical, bilateral, and found predominantly in the basal ganglia, thalamus, and cerebellum. So far, variants in three genes have been linked to PFBC: SLC20A2, PDGFRB, and PDGFB. Variants in SLC20A2 are responsible for most cases identified so far and, therefore, the present review is a comprehensive worldwide summary of all reported variants to date. SLC20A2 encodes an inorganic phosphate transporter, PiT-2, widely expressed in various tissues, including brain, and is part of a major family of solute carrier membrane transporters. Fifty variants reported in 55 unrelated patients so far have been identified in families of diverse ethnicities and only few are recurrent. Various types of variants were detected (missense, nonsense, frameshift) including full or partial SLC20A2 deletions. The recently reported SLC20A2 knockout mouse will enhance our understanding of disease mechanism and allow for screening of therapeutic compounds. In the present review, we also discuss the implications of these recent exciting findings and consider the possibility of treatments based on manipulation of inorganic phosphate homeostasis.

Lipoid proteinosis: phenotypic heterogeneity in Iranian families with c.507delT mutation in ECM1

Lipoid proteinosis (LP) is a rare autosomal recessive genodermatosis caused by loss-of-function mutations in the ECM1 gene, and previous studies have noted phenotypic variability. In this study, we examined 12 patients representing three Iranian families for clinical manifestations and genotyped them for mutations in ECM1. LP was diagnosed with characteristic mucocutaneous and neurologic manifestations. Five patients were also subjected to magnetic resonance imaging (MRI)/computed tomography (CT) scan of the central nervous system. DNA was isolated from peripheral blood from patients and their clinically unaffected relatives, and mutations in ECM1 were sought by PCR-based amplification of all exons and flanking intronic sequences, followed by bidirectional Sanger sequencing. Significant phenotypic variability in this multisystem disorder, including presence of convulsions and epilepsy in about half of the patients was noted. In most cases, this was associated with calcifications in the brain detected by MRI/CT scans. Genotyping of the affected individuals in three families from the central region of Iran revealed presence of homozygous c.507delT mutation in ECM1, reflecting the observed consanguinity in these families. This large cohort revealed extensive phenotypic variability in individuals with the same mutation in ECM1. This observation suggests a role for genetic and epigenetic as well as environmental modulation of the phenotype. Identification of mutations allows screening of unaffected individuals for presence or absence of this mutation in extended LP families, with implications for genetic counseling.

Idiopathic basal ganglia calcification-associated PDGFRB mutations impair the receptor signalling

Platelet-derived growth factors (PDGF) bind to two related receptor tyrosine kinases, which are encoded by the PDGFRA and PDGFRB genes. Recently, heterozygous PDGFRB mutations have been described in patients diagnosed with idiopathic basal ganglia calcification (IBGC or Fahr disease), a rare inherited neurological disorder. The goal of the present study was to determine whether these mutations had a positive or negative impact on the PDGFRB activity. We first showed that the E1071V mutant behaved like wild-type PDGFRB and may represent a polymorphism unrelated to IBGC. In contrast, the L658P mutant had no kinase activity and failed to activate any of the pathways normally stimulated by PDGF. The R987W mutant activated Akt and MAP kinases but did not induce the phosphorylation of signal transducer and activator of transcription 3 (STAT3) after PDGF stimulation. Phosphorylation of phospholipase Cγ was also decreased. Finally, we showed that the R987W mutant was more rapidly degraded upon PDGF binding compared to wild-type PDGFRB. In conclusion, PDGFRB mutations associated with IBGC impair the receptor signalling. PDGFRB loss of function in IBGC is consistent with recently described inactivating mutations in the PDGF-B ligand. These results raise concerns about the long-term safety of PDGF receptor inhibition by drugs such as imatinib.

Primary familial brain calcification: Genetic analysis and clinical spectrum

BACKGROUND

Primary familial brain calcification (PFBC) is a rare autosomal dominant disorder with bilateral calcification of basal ganglia and other cerebral regions, movement disorders, and neuropsychiatric disturbances. So far, three causative genes have been discovered: SLC20A2, PDGFRB and PDGFB, accounting for approximately 50% of cases.

METHODS

Seven unrelated families with primary brain calcification were recruited to undergo clinical and genetic analysis, including Sanger sequencing of SLC20A2, PDGFRB, and PDGFB, and copy number analysis of SLC20A2.

RESULTS

Mutations in SLC20A2 have been detected in three families: p.Glu368Glyfs*46, p.Ser434Trp, and p.Thr595Met. Intrafamilial phenotype variability has been observed. In spite of this, we found similar neuroimaging pattern among members of the same family.

CONCLUSIONS

This molecular analysis expands the mutational spectrum of SLC20A2, which remains the major causative gene of primary familial brain calcification, and suggests the existence of disease-causing mutations in at least another, still unknown gene.