Basal ganglia calcification in a patient with beta-propeller protein-associated neurodegeneration

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.

WDR45, one gene associated with multiple neurodevelopmental disorders

The WDR45 gene is localized on the X-chromosome and variants in this gene are linked to six different neurodegenerative disorders, i.e., ß-propeller protein associated neurodegeneration, Rett-like syndrome, intellectual disability, and epileptic encephalopathies including developmental and epileptic encephalopathy, early-onset epileptic encephalopathy and West syndrome and potentially also specific malignancies. WDR45/WIPI4 is a WD-repeat β-propeller protein that belongs to the WIPI (WD repeat domain, phosphoinositide interacting) family. The precise cellular function of WDR45 is still largely unknown, but deletions or conventional variants in WDR45 can lead to macroautophagy/autophagy defects, malfunctioning mitochondria, endoplasmic reticulum stress and unbalanced iron homeostasis, suggesting that this protein functions in one or more pathways regulating directly or indirectly those processes. As a result, the underlying cause of the WDR45-associated disorders remains unknown. In this review, we summarize the current knowledge about the cellular and physiological functions of WDR45 and highlight how genetic variants in its encoding gene may contribute to the pathophysiology of the associated diseases. In particular, we connect clinical manifestations of the disorders with their potential cellular origin of malfunctioning and critically discuss whether it is possible that one of the most prominent shared features, i.e., brain iron accumulation, is the primary cause for those disorders.

Abbreviations: ATG/Atg: autophagy related; BPAN: ß-propeller protein associated neurodegeneration; CNS: central nervous system; DEE: developmental and epileptic encephalopathy; EEG: electroencephalograph; ENO2/neuron-specific enolase, enolase 2; EOEE: early-onset epileptic encephalopathy; ER: endoplasmic reticulum; ID: intellectual disability; IDR: intrinsically disordered region; MRI: magnetic resonance imaging; NBIA: neurodegeneration with brain iron accumulation; NCOA4: nuclear receptor coactivator 4; PtdIns3P: phosphatidylinositol-3-phosphate; RLS: Rett-like syndrome; WDR45: WD repeat domain 45; WIPI: WD repeat domain, phosphoinositide interacting

Brain MRI Pattern Recognition in Neurodegeneration With Brain Iron Accumulation

Most neurodegeneration with brain iron accumulation (NBIA) disorders can be distinguished by identifying characteristic changes on magnetic resonance imaging (MRI) in combination with clinical findings. However, a significant number of patients with an NBIA disorder confirmed by genetic testing have MRI features that are atypical for their specific disease. The appearance of specific MRI patterns depends on the stage of the disease and the patient's age at evaluation. MRI interpretation can be challenging because of heterogeneously acquired MRI datasets, individual interpreter bias, and lack of quantitative data. Therefore, optimal acquisition and interpretation of MRI data are needed to better define MRI phenotypes in NBIA disorders. The stepwise approach outlined here may help to identify NBIA disorders and delineate the natural course of MRI-identified changes.

[Basal ganglia calcification]

Calcifications of the basal ganglia are frequently seen on the cerebral CT scans and particularly in the globus pallidus. Their frequency increases physiologically with age after 50 years old. However, pathological processes can also be associated with calcium deposits in the gray nuclei, posterior fossa or white matter. Unilateral calcification is often related to an acquired origin whereas bilateral ones are mostly linked to an acquired or genetic origin that will be sought after eliminating a perturbation of phosphocalcic metabolism. In pathological contexts, these calcifications may be accompanied by neurological symptoms related to the underlying disease: Parkinson's syndrome, psychiatric and cognitive disorders, epilepsy or headache. The purpose of this article is to provide a diagnostic aid, in addition to clinical and biology, through the analysis of calcification topography and the study of different MRI sequences.

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

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

Beta-propeller protein-associated neurodegeneration: a case report and review of the literature

Beta‐propeller protein‐associated neurodegeneration (BPAN) is a rare disorder, which is increasingly recognized thanks to next‐generation sequencing. Due to a highly variable phenotype, patients may present to pediatrics, neurology, psychiatry, or internal medicine. It is therefore essential that physicians of different specialties are familiar with this severe and debilitating condition.

Brain Calcification and Movement Disorders

Brain calcifications may be an incidental finding on neuroimaging in normal, particularly older individuals, but can also indicate numerous hereditary and nonhereditary syndromes, and metabolic, environmental, infectious, autoimmune, mitochondrial, traumatic, or toxic disorders. Bilateral calcifications most commonly affecting the basal ganglia may often be found in idiopathic cases, and a new term, primary familial brain calcification (PFBC), has been proposed that recognizes the genetic causes of the disorder and that calcifications occurred well beyond the basal ganglia. PFBC, usually inherited in an autosomal dominant fashion, is both an intrafamilial and an interfamilial heterogeneous disorder, clinically characterized by an insidious and progressive development of movement disorders, cognitive decline, and psychiatric symptoms, but also cerebellar ataxia, pyramidal signs, and sometimes isolated seizures and headaches/migraines. Heterozygous mutations in four genes (SLC20A2, PDGFRB, PDGFB, XPR1) have recently proved to be the causes of the autosomal dominant forms of PFBC, also suggesting disrupted phosphate homeostasis as "an underlying and converging" pathophysiological mechanism. However, to date, it is not possible to anticipate with acceptable certainty any of known genetic causes of PFBC on the basis of the type, severity, pattern of distribution, or combination of movement disorders (mainly parkinsonism, with or without tremor, but also dystonia, chorea, paroxysmal kinesigenic dyskinesia, orofacial dyskinesia, and gait and speech disorders).

The Impact of Early Bilingualism on Face Recognition Processes

Early linguistic experience has an impact on the way we decode audiovisual speech in face-to-face communication. The present study examined whether differences in visual speech decoding could be linked to a broader difference in face processing. To identify a phoneme we have to do an analysis of the speaker's face to focus on the relevant cues for speech decoding (e.g., locating the mouth with respect to the eyes). Face recognition processes were investigated through two classic effects in face recognition studies: the Other-Race Effect (ORE) and the Inversion Effect. Bilingual and monolingual participants did a face recognition task with Caucasian faces (own race), Chinese faces (other race), and cars that were presented in an Upright or Inverted position. The results revealed that monolinguals exhibited the classic ORE. Bilinguals did not. Overall, bilinguals were slower than monolinguals. These results suggest that bilinguals' face processing abilities differ from monolinguals'. Early exposure to more than one language may lead to a perceptual organization that goes beyond language processing and could extend to face analysis. We hypothesize that these differences could be due to the fact that bilinguals focus on different parts of the face than monolinguals, making them more efficient in other race face processing but slower. However, more studies using eye-tracking techniques are necessary to confirm this explanation.

WDR45 mutations in Rett (-like) syndrome and developmental delay: Case report and an appraisal of the literature

Mutations in the WDR45 gene have been identified as causative for the only X-linked type of neurodegeneration with brain iron accumulation (NBIA), clinically characterized by global developmental delay in childhood, followed by a secondary neurological decline with parkinsonism and/or dementia in adolescence or early adulthood. Recent reports suggest that WDR45 mutations are associated with a broader phenotypic spectrum. We identified a novel splice site mutation (c.440-2 A > G) in a 5-year-old Argentinian patient with Rett-like syndrome, exhibiting developmental delay, microcephaly, seizures and stereotypic hand movements, and discuss this finding, together with a review of the literature. Additional patients with a clinical diagnosis of Rett (-like) syndrome were also found to carry WDR45 mutations before (or without) clinical decline or signs of iron accumulation by magnetic resonance imaging (MRI). This information indicates that WDR45 mutations should be added to the growing list of genetic alterations linked to Rett-like syndrome. Further, clinical symptoms associated with WDR45 mutations ranged from early-onset epileptic encephalopathy in a male patient with a deletion of WDR45 to only mild cognitive delay in a female patient, suggesting that analysis of this gene should be considered more often in patients with developmental delay, regardless of severity. The increasing use of next generation sequencing technologies as well as longitudinal follow-up of patients with an early diagnosis will help to gain additional insight into the phenotypic spectrum associated with WDR45 mutations.

Congenital disorders of autophagy: an emerging novel class of inborn errors of neuro-metabolism

Single gene disorders of the autophagy pathway are an emerging, novel and diverse group of multisystem diseases in children. Clinically, these disorders prominently affect the central nervous system at various stages of development, leading to brain malformations, developmental delay, intellectual disability, epilepsy, movement disorders, and neurodegeneration, among others. Frequent early and severe involvement of the central nervous system puts the paediatric neurologist, neurogeneticist, and neurometabolic specialist at the forefront of recognizing and treating these rare conditions. On a molecular level, mutations in key autophagy genes map to different stages of this highly conserved pathway and thus lead to impairment in isolation membrane (or phagophore) and autophagosome formation, maturation, or autophagosome-lysosome fusion. Here we discuss 'congenital disorders of autophagy' as an emerging subclass of inborn errors of metabolism by using the examples of six recently identified monogenic diseases: EPG5-related Vici syndrome, beta-propeller protein-associated neurodegeneration due to mutations in WDR45, SNX14-associated autosomal-recessive cerebellar ataxia and intellectual disability syndrome, and three forms of hereditary spastic paraplegia, SPG11, SPG15 and SPG49 caused by SPG11, ZFYVE26 and TECPR2 mutations, respectively. We also highlight associations between defective autophagy and other inborn errors of metabolism such as lysosomal storage diseases and neurodevelopmental diseases associated with the mTOR pathway, which may be included in the wider spectrum of autophagy-related diseases from a pathobiological point of view. By exploring these emerging themes in disease pathogenesis and underlying pathophysiological mechanisms, we discuss how congenital disorders of autophagy inform our understanding of the importance of this fascinating cellular pathway for central nervous system biology and disease. Finally, we review the concept of modulating autophagy as a therapeutic target and argue that congenital disorders of autophagy provide a unique genetic perspective on the possibilities and challenges of pathway-specific drug development.

Lessons from a pair of siblings with BPAN

Neurodegeneration with brain iron accumulation (NBIA) encompasses a heterogeneous group of inherited progressive neurological diseases. Beta-propeller protein-associated neurodegeneration (BPAN) has been estimated to account for ~7% of all cases of NBIA and has distinctive clinical and brain imaging findings. Heterozygous variants in the WDR45 gene located in Xp11.23 are responsible for BPAN. A clear female predominance supports an X-linked dominant pattern of inheritance with proposed lethality for germline variants in hemizygous males. By whole-exome sequencing, we identified an in-frame deletion in the WDR45 gene (c.161_163delTGG) in the hemizygous state in a 20-year-old man with a history of profound neurocognitive impairment and seizures. His higher functioning 14-year-old sister, also with a history of intellectual disability, was found to carry the same variant in the heterozygous state. Their asymptomatic mother was mosaic for the alteration. From this pair of siblings with BPAN we conclude that: (1) inherited WDR45 variants are possible, albeit rare; (2) hemizygous germline variants in males can be viable, but likely result in a more severe phenotype; (3) for siblings with germline variants, males should be more significantly affected than females; and (4) because gonadal and germline mosaicism are possible and healthy female carriers can be found, parental testing for variants in WDR45 should be considered.

Genetics and molecular biology of brain calcification

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