Early manifestations of BPAN in a pediatric patient

Rett Syndrome Spectrum in Monogenic Developmental-Epileptic Encephalopathies and Epilepsies: A Review

INTRODUCTION

Progress in the clinical application of next-generation-sequencing-based techniques has resulted in a dramatic increase in the recognized genetic heterogeneity of the Rett syndrome spectrum (RSS). Our awareness of the considerable overlap with pediatric-onset epilepsies and epileptic/developmental encephalopathies (EE/DE) genes is also growing, and the presence of variable clinical features inside a general frame of commonalities has drawn renewed attention into deep phenotyping.

METHODS

We decided to review the medical literature on atypical Rett syndrome and "Rett-like" phenotypes, with special emphasis on described cases with pediatric-onset epilepsies and/or EE-DE, evaluating Neul's criteria for Rett syndrome and associated movement disorders and notable stereotypies.

RESULTS

"Rett-like" features were described in syndromic and non-syndromic monogenic epilepsy- and DE/EE-related genes, in "intellectual disability plus epilepsy"-related genes and in neurodegenerative disorders. Additionally, prominent stereotypies can be observed in monogenic complex neurodevelopmental disorders featuring epilepsy with or without autistic features outside of the RSS.

CONCLUSIONS

Patients share a complex neurodevelopmental and neurological phenotype (developmental delay, movement disorder) with impaired gait, abnormal tone and hand stereotypies. However, the presence and characteristics of regression and loss of language and functional hand use can differ. Finally, the frequency of additional supportive criteria and their distribution also vary widely.

A comprehensive phenotypic characterization of a whole-body Wdr45 knock-out mouse

Pathogenic variants in the WDR45 (OMIM: 300,526) gene on chromosome Xp11 are the genetic cause of a rare neurological disorder characterized by increased iron deposition in the basal ganglia. As WDR45 encodes a beta-propeller scaffold protein with a putative role in autophagy, the disease has been named Beta-Propeller Protein-Associated Neurodegeneration (BPAN). BPAN represents one of the four most common forms of Neurodegeneration with Brain Iron Accumulation (NBIA). In the current study, we generated and characterized a whole-body Wdr45 knock-out (KO) mouse model. The model, developed using TALENs, presents a 20-bp deletion in exon 2 of Wdr45. Homozygous females and hemizygous males are viable, proving that systemic depletion of Wdr45 does not impair viability and male fertility in mice. The in-depth phenotypic characterization of the mouse model revealed neuropathology signs at four months of age, neurodegeneration progressing with ageing, hearing and visual impairment, specific haematological alterations, but no brain iron accumulation. Biochemically, Wdr45 KO mice presented with decreased complex I (CI) activity in the brain, suggesting that mitochondrial dysfunction accompanies Wdr45 deficiency. Overall, the systemic Wdr45 KO described here complements the two mouse models previously reported in the literature (PMIDs: 26,000,824, 31,204,559) and represents an additional robust model to investigate the pathophysiology of BPAN and to test therapeutic strategies for the disease.

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

Beta-propeller protein-associated neurodegeneration presenting Rett-like features: A case report and literature review

Several patients with beta-propeller protein-associated neurodegeneration (BPAN)/static encephalopathy with neurodegeneration in adulthood have been reported to present Rett syndrome (RTT)-like features. This report presents an individual with BPAN showing clinical features of RTT. Psychomotor delay and epilepsy onset were noted at 1 year, and regression began at 4 years. Screening of the methyl-CpG binding protein 2 (MECP2) did not show variants. At 22 years, basal ganglia iron deposits were found on magnetic resonance imaging (MRI), and the WD-domain repeat 45 gene (WDR45) variant was identified. Review of the literature showed that BPAN with RTT-like features is associated with more epileptic seizures and less deceleration of head growth, breathing irregularities, and cold extremities than classic RTT with MECP2 variants. These clinical presentations may provide clues for differentiating between these two disorders. However, both WDR45 and MECP2 should be screened in patients presenting a clinical picture of RTT without specific MRI findings of BPAN.

Phenotypic and Imaging Spectrum Associated With WDR45

BACKGROUND

Mutations in the X-linked gene WDR45 cause neurodegeneration with brain iron accumulation type 5. Global developmental delay occurs at an early age with slow progression to dystonia, parkinsonism, and dementia due to progressive iron accumulation in the brain.

METHODS

We present 17 new cases and reviewed 106 reported cases of neurodegeneration with brain iron accumulation type 5. Detailed information related to developmental history and key time to event measures was collected.

RESULTS

Within this cohort, there were 19 males. Most individuals were molecularly diagnosed by whole-exome testing. Overall 10 novel variants were identified across 11 subjects. All individuals were affected by developmental delay, most prominently in verbal skills. Most individuals experienced a decline in motor and cognitive skills. Although most individuals were affected by seizures, the spectrum ranged from provoked seizures to intractable epilepsy. The imaging findings varied as well, often evolving over time. The classic iron accumulation in the globus pallidus and substantia nigra was noted in half of our cohort and was associated with older age of image acquisition, whereas myelination abnormalities were associated with younger age.

CONCLUSIONS

WDR45 mutations lead to a progressive and evolving disorder whose diagnosis is often delayed. Developmental delay and seizures predominate in early childhood, followed by a progressive decline of neurological function. There is variable expressivity in the clinical phenotypes of individuals with WDR45 mutations, suggesting that this gene should be considered in the diagnostic evaluation of children with myelination abnormalities, iron deposition, developmental delay, and epilepsy depending on the age at evaluation.

[A case of novel WDR45 mutation with beta-propeller protein-associated neurodegeneration (BPAN) presenting asymmetrical extrapyramidal signs]

Beta-propeller protein-associated neurodegeneration (BPAN) is categorized in Neurodegeneration with brain iron accumulation. The clinical feature of BPAN is global developmental delay in early childhood, followed rapid progression of cognitive disfunction and parkinsonism in adulthood. This case was pointed out intellectual disability at the age of 9, followed left dominant progressive parkinsonism from the age of 31. Brain MRI showed the T₁-weighted signal hyperintensity of the substantia nigra with a central band of hypointensity and the T₂ star weighted image hypointensity of substantia nigra and globus pallidus presenting dominant at right side. DAT SPECT also showed specific binding ratio decreased dominant in right side. She was diagnosed BPAN based on her genetic test revealing a novel mutation (c.411dupT) in WDR45. No studies reported detailed parkinsonism like laterality in BPAN. This case indicates the left dominant parkinsonism was caused by right dominant iron deposition to substantia nigra and globus pallidus in view of MRI findings and DAT SPECT.

Novel insights into the clinical and molecular spectrum of congenital disorders of autophagy

Autophagy is a fundamental and conserved catabolic pathway that mediates the degradation of macromolecules and organelles in lysosomes. Autophagy is particularly important to postmitotic and metabolically active cells such as neurons. The complex architecture of neurons and their long axons pose additional challenges for efficient recycling of cargo. Not surprisingly autophagy is required for normal central nervous system development and function. Several single-gene disorders of the autophagy pathway have been discovered in recent years giving rise to a novel group of inborn errors of metabolism referred to as congenital disorders of autophagy. While these disorders are heterogeneous, they share several clinical and molecular characteristics including a prominent and progressive involvement of the central nervous system leading to brain malformations, developmental delay, intellectual disability, epilepsy, movement disorders, and cognitive decline. On brain magnetic resonance imaging a predominant involvement of the corpus callosum, the corticospinal tracts and the cerebellum are noted. A storage disease phenotype is present in some diseases, underscoring both clinical and molecular overlaps to lysosomal storage diseases. This review provides an update on the clinical, imaging, and genetic spectrum of congenital disorders of autophagy and highlights the importance of this pathway for neurometabolism and childhood-onset neurological diseases.

Single-center experience with Beta-propeller protein-associated neurodegeneration (BPAN); expanding the phenotypic spectrum

Beta-propeller protein-associated neurodegeneration (BPAN) is a subtype of neurodegeneration with brain iron accumulation (NBIA) that presents with childhood developmental delay (especially speech delay), occasionally associated with epileptic encephalopathy, autism, or Rett-like syndrome. The majority of children described to date have been severely affected, with little to no expressive speech function, severe developmental delay, and cognitive impairment. Herein, five additional patients with BPAN identified in the same center in Canada are described, four with the typical severe phenotype and one with a milder phenotype. Our findings provide further evidence that a spectrum of severity exists for this rare and newly described condition. Challenges in identifying iron accumulation on brain MRI are also addressed. Additionally, the importance of including the WDR45 gene on epilepsy and Rett-like syndrome genetic panels is highlighted.

Substantia Nigra Swelling and Dentate Nucleus T2 Hyperintensity May Be Early Magnetic Resonance Imaging Signs of β-Propeller Protein-Associated Neurodegeneration

Background and Methods

Mutations in WDR45 cause β-propeller protein-associated neurodegeneration (BPAN), a type of neurodegeneration with brain iron accumulation (NBIA). We reviewed clinical and MRI findings in 4 patients with de novo WDR45 mutations.

Results

Psychomotor delay and movement disorders were present in all cases; early-onset epileptic encephalopathy was present in 3. In all cases, first MRI showed: prominent bilateral SN enlargement, bilateral dentate nuclei T2-hyperintensity, and corpus callosum thinning. Iron deposition in the SN and globus pallidus (GP) only became evident later. Diffuse cerebral atrophy was present in 3 cases.

Conclusions

In this series, SN swelling and dentate nucleus T2 hyperintensity were early signs of BPAN, later followed by progressive iron deposition in the SN and GP. When clinical suspicion is raised, MRI is crucial for identifying early features suggesting this type of NBIA.

Ocular and systemic manifestations of beta-propeller protein-associated neurodegeneration

Beta-propeller protein-associated neurodegeneration (BPAN) is a rare genetic disorder characterized by neurodegeneration with brain iron accumulation (NBIA). We report an infant diagnosed with BPAN who was found to have high myopia and astigmatism, strabismus, and bilateral retinal pigmentary changes. While retinal pigmentary changes have been described in other disorders of NBIA, it has been only rarely reported in BPAN.

Monogenic disorders that mimic the phenotype of Rett syndrome

Rett syndrome (RTT) is caused by mutations in methyl-CpG-binding protein 2 (MECP2), but defects in a handful of other genes (e.g., CDKL5, FOXG1, MEF2C) can lead to presentations that resemble, but do not completely mirror, classical RTT. In this study, we attempted to identify other monogenic disorders that share features with RTT. We performed a retrospective chart review on n = 319 patients who had undergone clinical whole exome sequencing (WES) for further etiological evaluation of neurodevelopmental diagnoses that remained unexplained despite extensive prior workup. From this group, we characterized those who (1) possessed features that were compatible with RTT based on clinical judgment, (2) subsequently underwent MECP2 sequencing and/or MECP2 deletion/duplication analysis with negative results, and (3) ultimately arrived at a diagnosis other than RTT with WES. n = 7 patients had clinical features overlapping RTT with negative MECP2 analysis but positive WES providing a diagnosis. These seven patients collectively possessed pathogenic variants in six different genes: two in KCNB1 and one each in FOXG1, IQSEC2, MEIS2, TCF4, and WDR45. n = 2 (both with KCNB1 variants) fulfilled criteria for atypical RTT. RTT-associated features included the following: loss of hand or language skills (n = 3; IQSEC2, KCNB1 x 2); disrupted sleep (n = 4; KNCB1, MEIS2, TCF4, WDR45); stereotyped hand movements (n = 5; FOXG1, KNCB1 x 2, MEIS2, TCF4); bruxism (n = 3; KCNB1 x 2; TCF4); and hypotonia (n = 7). Clinically based diagnoses can be misleading, evident by the increasing number of genetic conditions associated with features of RTT with negative MECP2 mutations.

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.

Variations of stereotypies in individuals with Rett syndrome: A nationwide cross-sectional study in Taiwan

Individuals with Rett syndrome (RTT) can have variable manifestations of stereotypies. In this nation-wide cross-sectional study, we recruited all individuals with RTT in Taiwan diagnosed as RTT by neurologists based on genetic findings and diagnostic criteria. The data were collected using questionnaire. A total 43 cases of typical RTT and 15 cases of atypical RTT, aged from 2.1 to 40.1 years, were enrolled. They included 3 (5.2%) in stage II, 42 (72.4%) in stage III, and 13 (22.4%) in stage IV. All individuals presented with at least one stereotypy. Individuals with atypical RTT had more varied stereotypies (mean: 14 ± 6) compared to those with typical RTT (mean: 9 ± 5) (P = 0.003). Flapping (73.3%) and wringing (58.1%) were the most common hand stereotypies in atypical and typical RTT, respectively. Compared with typical RTT, hair pulling, bruxism, retropulsion, and protrusion of lips were more common in atypical RTT (P = 0.003, P = 0.006, P = 0.003 and <0.001, respectively). The number of stereotypies did not differ among different stages, clinical severities, and hand functions. Although there were no age-related changes in stereotypies in atypical RTT, flapping (P = 0.012), clapping (P = 0.044), and mouthing with single hand (P = 0.009) were significantly more prevalent in individuals aged <10 years with typical RTT, and they decreased after 10 years. In conclusion, our study showed that the stereotypical movements varied in typical and atypical RTT, implying the heterogeneous nature of the disease and the pathogenic mechanisms of RTT with atypical features. Autism Res 2017. © 2017 International Society for Autism Research, Wiley Periodicals, Inc. Autism Res 2017, 10: 1204-1214. © 2017 International Society for Autism Research, Wiley Periodicals, Inc.

Autistic Siblings with Novel Mutations in Two Different Genes: Insight for Genetic Workups of Autistic Siblings and Connection to Mitochondrial Dysfunction

The prevalence of autism spectrum disorder (ASD) is high, yet the etiology of this disorder is still uncertain. Advancements in genetic analysis have provided the ability to identify potential genetic changes that may contribute to ASD. Interestingly, several genetic syndromes have been linked to metabolic dysfunction, suggesting an avenue for treatment. In this case study, we report siblings with ASD who had similar initial phenotypic presentations. Whole exome sequencing (WES) revealed a novel c.795delT mutation in the WDR45 gene affecting the girl, which was consistent with her eventual progression to a Rett-like syndrome phenotype including seizures along with a stereotypical cyclic breathing pattern. Interestingly, WES identified that the brother harbored a novel heterozygous Y1546H variant in the DEP domain-containing protein 5 (DEPDC5) gene, consistent with his presentation. Both siblings underwent a metabolic workup that demonstrated different patterns of mitochondrial dysfunction. The girl demonstrated statistically significant elevations in mitochondrial activity of complex I + III in both muscle and fibroblasts and increased respiration in peripheral blood mononuclear cells (PBMCs) on Seahorse Extracellular Flux analysis. The boy demonstrates a statistically significant decrease in complex IV activity in buccal epithelium and decreased respiration in PBMCs. These cases highlight the differences in genetic abnormalities even in siblings with ASD phenotypes as well as highlights the individual role of novel mutations in the WDR45 and DEPDC5 genes. These cases demonstrate the importance of advanced genetic testing combined with metabolic evaluations in the workup of children with ASD.

Brain iron accumulation affects myelin-related molecular systems implicated in a rare neurogenetic disease family with neuropsychiatric features

The 'neurodegeneration with brain iron accumulation' (NBIA) disease family entails movement or cognitive impairment, often with psychiatric features. To understand how iron loading affects the brain, we studied mice with disruption of two iron regulatory genes, hemochromatosis (Hfe) and transferrin receptor 2 (Tfr2). Inductively coupled plasma atomic emission spectroscopy demonstrated increased iron in the Hfe^-/- × Tfr2^mut brain (P=0.002, n ≥5/group), primarily localized by Perls' staining to myelinated structures. Western immunoblotting showed increases of the iron storage protein ferritin light polypeptide and microarray and real-time reverse transcription-PCR revealed decreased transcript levels (P<0.04, n ≥5/group) for five other NBIA genes, phospholipase A2 group VI, fatty acid 2-hydroxylase, ceruloplasmin, chromosome 19 open reading frame 12 and ATPase type 13A2. Apart from the ferroxidase ceruloplasmin, all are involved in myelin homeostasis; 16 other myelin-related genes also showed reduced expression (P<0.05), although gross myelin structure and integrity appear unaffected (P>0.05). Overlap (P<0.0001) of differentially expressed genes in Hfe^-/- × Tfr2^mut brain with human gene co-expression networks suggests iron loading influences expression of NBIA-related and myelin-related genes co-expressed in normal human basal ganglia. There was overlap (P<0.0001) of genes differentially expressed in Hfe^-/- × Tfr2^mut brain and post-mortem NBIA basal ganglia. Hfe^-/- × Tfr2^mut mice were hyperactive (P<0.0112) without apparent cognitive impairment by IntelliCage testing (P>0.05). These results implicate myelin-related systems involved in NBIA neuropathogenesis in early responses to iron loading. This may contribute to behavioral symptoms in NBIA and hemochromatosis and is relevant to patients with abnormal iron status and psychiatric disorders involving myelin abnormalities or resistant to conventional treatments.

Pathological relationships involving iron and myelin may constitute a shared mechanism linking various rare and common brain diseases

We previously demonstrated elevated brain iron levels in myelinated structures and associated cells in a hemochromatosis Hfe^−/−xTfr2^mut mouse model. This was accompanied by altered expression of a group of myelin-related genes, including a suite of genes causatively linked to the rare disease family ‘neurodegeneration with brain iron accumulation’ (NBIA). Expanded data mining and ontological analyses have now identified additional myelin-related transcriptome changes in response to brain iron loading. Concordance between the mouse transcriptome changes and human myelin-related gene expression networks in normal and NBIA basal ganglia testifies to potential clinical relevance. These analyses implicate, among others, genes linked to various rare central hypomyelinating leukodystrophies and peripheral neuropathies including Pelizaeus-Merzbacher-like disease and Charcot-Marie-Tooth disease as well as genes linked to other rare neurological diseases such as Niemann-Pick disease. The findings may help understand interrelationships of iron and myelin in more common conditions such as hemochromatosis, multiple sclerosis and various psychiatric disorders.

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.

Novel WDR45 Mutation and Pathognomonic BPAN Imaging in a Young Female With Mild Cognitive Delay

β-propeller protein-associated neurodegeneration (BPAN) is a recently identified X-linked dominant form of neurodegeneration with brain iron accumulation caused by mutations in the WDR45 gene. BPAN commonly presents as global developmental delay in childhood with rapid onset of parkinsonism and dementia in early adulthood and associated pathognomonic changes seen on brain MRI. In this case report, we present a pediatric patient with mild cognitive delay and pathognomonic MRI changes indicative of BPAN preceding neurologic deterioration who is found to have a novel de novo mutation in the WDR45 gene.

The Utility of Next-Generation Sequencing in Gene Discovery for Mutation-Negative Patients with Rett Syndrome

Rett syndrome (RTT) is a rare, severe disorder of neuronal plasticity that predominantly affects girls. Girls with RTT usually appear asymptomatic in the first 6–18 months of life, but gradually develop severe motor, cognitive, and behavioral abnormalities that persist for life. A predominance of neuronal and synaptic dysfunction, with altered excitatory–inhibitory neuronal synaptic transmission and synaptic plasticity, are overarching features of RTT in children and in mouse models. Over 90% of patients with classical RTT have mutations in the X-linked methyl-CpG-binding (MECP2) gene, while other genes, including cyclin-dependent kinase-like 5 (CDKL5), Forkhead box protein G1 (FOXG1), myocyte-specific enhancer factor 2C (MEF2C), and transcription factor 4 (TCF4), have been associated with phenotypes overlapping with RTT. However, there remain a proportion of patients who carry a clinical diagnosis of RTT, but who are mutation negative. In recent years, next-generation sequencing technologies have revolutionized approaches to genetic studies, making whole-exome and even whole-genome sequencing possible strategies for the detection of rare and de novo mutations, aiding the discovery of novel disease genes. Here, we review the recent progress that is emerging in identifying pathogenic variations, specifically from exome sequencing in RTT patients, and emphasize the need for the use of this technology to identify known and new disease genes in RTT patients.