Biallelic KITLG variants lead to a distinct spectrum of hypomelanosis and sensorineural hearing loss.

BACKGROUND: Pathogenic variants in KITLG, a crucial protein involved in pigmentation and neural crest cell migration, cause non-syndromic hearing loss, Waardenburg syndrome type 2, familial progressive hyperpigmentation and familial progressive hyper- and hypopigmentation, all of which are inherited in an autosomal dominant manner. OBJECTIVES: To describe the genotypic and clinical spectrum of biallelic KITLG-variants. METHODS: We used a genotype-first approach through the GeneMatcher data sharing platform to collect individuals with biallelic KITLG variants and reviewed the literature for overlapping reports. RESULTS: We describe the first case series with biallelic KITLG variants; we expand the known hypomelanosis spectrum to include a 'sock-and-glove-like', symmetric distribution, progressive repigmentation and generalized hypomelanosis. We speculate that KITLG biallelic loss-of-function variants cause generalized hypomelanosis, whilst variants with residual function lead to a variable auditory-pigmentary disorder mostly reminiscent of Waardenburg syndrome type 2 or piebaldism. CONCLUSIONS: We provide consolidating evidence that biallelic KITLG variants cause a distinct auditory-pigmentary disorder. We evidence a significant clinical variability, similar to the one previously observed in KIT-related piebaldism.

Baseline factors associated with early and late death in intracerebral haemorrhage survivors.

BACKGROUND AND PURPOSE: The aim of this study was to determine whether early and late death are associated with different baseline factors in intracerebral haemorrhage (ICH) survivors. METHODS: This was a secondary analysis of the multicentre prospective observational CROMIS-2 ICH study. Death was defined as 'early' if occurring within 6 months of study entry and 'late' if occurring after this time point. RESULTS: In our cohort (n = 1094), there were 306 deaths (per 100 patient-years: absolute event rate, 11.7; 95% confidence intervals, 10.5-13.1); 156 were 'early' and 150 'late'. In multivariable analyses, early death was independently associated with age [per year increase; hazard ratio (HR), 1.05, P = 0.003], history of hypertension (HR, 1.89, P = 0.038), pre-event modified Rankin scale score (per point increase; HR, 1.41, P < 0.0001), admission National Institutes of Health Stroke Scale score (per point increase; HR, 1.11, P < 0.0001) and haemorrhage volume >60 mL (HR, 4.08, P < 0.0001). Late death showed independent associations with age (per year increase; HR, 1.04, P = 0.003), pre-event modified Rankin scale score (per point increase; HR, 1.42, P = 0.001), prior anticoagulant use (HR, 2.13, P = 0.028) and the presence of intraventricular extension (HR, 1.73, P = 0.033) in multivariable analyses. In further analyses where time was treated as continuous (rather than dichotomized), the HR of previous cerebral ischaemic events increased with time, whereas HRs for Glasgow Coma Scale score, National Institutes of Health Stroke Scale score and ICH volume decreased over time. CONCLUSIONS: We provide new evidence that not all baseline factors associated with early mortality after ICH are associated with mortality after 6 months and that the effects of baseline variables change over time. Our findings could help design better prognostic scores for later death after ICH.

Genetic and phenotypic characterization of NKX6-2-related spastic ataxia and hypomyelination.

BACKGROUND AND PURPOSE: Hypomyelinating leukodystrophies are a heterogeneous group of genetic disorders with a wide spectrum of phenotypes and a high rate of genetically unsolved cases. Bi-allelic mutations in NKX6-2 were recently linked to spastic ataxia 8 with hypomyelinating leukodystrophy. METHODS: Using a combination of homozygosity mapping, exome sequencing, and detailed clinical and neuroimaging assessment a series of new NKX6-2 mutations in a multicentre setting is described. Then, all reported NKX6-2 mutations and those identified in this study were combined and an in-depth analysis of NKX6-2-related disease spectrum was provided. RESULTS: Eleven new cases from eight families of different ethnic backgrounds carrying compound heterozygous and homozygous pathogenic variants in NKX6-2 were identified, evidencing a high NKX6-2 mutation burden in the hypomyelinating leukodystrophy disease spectrum. Our data reveal a phenotype spectrum with neonatal onset, global psychomotor delay and worse prognosis at the severe end and a childhood onset with mainly motor phenotype at the milder end. The phenotypic and neuroimaging expression in NKX6-2 is described and it is shown that phenotypes with epilepsy in the absence of overt hypomyelination and diffuse hypomyelination without seizures can occur. CONCLUSIONS: NKX6-2 mutations should be considered in patients with autosomal recessive, very early onset of nystagmus, cerebellar ataxia with hypotonia that rapidly progresses to spasticity, particularly when associated with neuroimaging signs of hypomyelination. Therefore, it is recommended that NXK6-2 should be included in hypomyelinating leukodystrophy and spastic ataxia diagnostic panels.

Predictors for a dementia gene mutation based on gene-panel next-generation sequencing of a large dementia referral series.

Next-generation genetic sequencing (NGS) technologies facilitate the screening of multiple genes linked to neurodegenerative dementia, but there are few reports about their use in clinical practice. Which patients would most profit from testing, and information on the likelihood of discovery of a causal variant in a clinical syndrome, are conspicuously absent from the literature, mostly for a lack of large-scale studies. We applied a validated NGS dementia panel to 3241 patients with dementia and healthy aged controls; 13,152 variants were classified by likelihood of pathogenicity. We identified 354 deleterious variants (DV, 12.6% of patients); 39 were novel DVs. Age at clinical onset, clinical syndrome and family history each strongly predict the likelihood of finding a DV, but healthcare setting and gender did not. DVs were frequently found in genes not usually associated with the clinical syndrome. Patients recruited from primary referral centres were compared with those seen at higher-level research centres and a national clinical neurogenetic laboratory; rates of discovery were comparable, making selection bias unlikely and the results generalisable to clinical practice. We estimated penetrance of DVs using large-scale online genomic population databases and found 71 with evidence of reduced penetrance. Two DVs in the same patient were found more frequently than expected. These data should provide a basis for more informed counselling and clinical decision making.

A 30-year history of MPAN case from Russia.

We present a patient with progressive spastic ataxia, with dystonia and anarthria undiagnosed until detailed genetic analysis revealed an MPAN mutation. Highlighting the worldwide MPAN distribution, a 30year history of absent diagnosis and the impact and cost saving of an early but detailed genetic analysis in complex progressive movement disorders, particularly the anarthric NBIA group.

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-/- × Tfr2mut 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-/- × Tfr2mut 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-/- × Tfr2mut brain and post-mortem NBIA basal ganglia. Hfe-/- × Tfr2mut 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.

Genome-wide estimate of the heritability of Multiple System Atrophy.

INTRODUCTION: Multiple System Atrophy (MSA) is a neurodegenerative disease which presents heterogeneously with symptoms and signs of parkinsonism, ataxia and autonomic dysfunction. Although MSA typically occurs sporadically, rare pathology-proven MSA families following either autosomal recessive or autosomal dominant patterns have been described, indicating a heritable contribution to the pathogenesis. METHODS: We used Genome-Wide Complex Trait Analysis (GCTA) to estimate the heritable component of MSA due to common coding variability in imputed genotype data of 907 MSA cases and 3866 population-matched controls. GCTA only assesses the effect of putative causal variants in linkage disequilibrium (LD) with all common SNPs on the genotyping platform. RESULTS: We estimate the heritability among common variants of MSA in pooled cases at 2.09-6.65%, with a wider range of values in geographic and diagnostic subgroups. Meta-analysis of our geographic cohorts reveals high between-group heterogeneity. Contributions of single chromosomes are generally negligible. We suggest that all calculated MSA heritability among common variants could be explained by the presence of misdiagnosed cases in the clinical subgroup based on a Bayesian estimate using literature-derived rates of misdiagnosis. DISCUSSION: MSA is a challenging disease to study due to high rates of misdiagnosis and low prevalence. Given our low estimates of heritability, common genetic variation appears to play a less prominent role in risk for MSA than in other complex neurodegenerative diseases such as Parkinson's disease, Alzheimer's disease, and Amyotrophic Lateral Sclerosis. The success of future gene discovery efforts rests on large pathologically-confirmed case series and an interrogation of both common and rare genetic variants.

Review: Insights into molecular mechanisms of disease in neurodegeneration with brain iron accumulation: unifying theories.

Neurodegeneration with brain iron accumulation (NBIA) is a group of disorders characterized by dystonia, parkinsonism and spasticity. Iron accumulates in the basal ganglia and may be accompanied by Lewy bodies, axonal swellings and hyperphosphorylated tau depending on NBIA subtype. Mutations in 10 genes have been associated with NBIA that include Ceruloplasmin (Cp) and ferritin light chain (FTL), both directly involved in iron homeostasis, as well as Pantothenate Kinase 2 (PANK2), Phospholipase A2 group 6 (PLA2G6), Fatty acid hydroxylase 2 (FA2H), Coenzyme A synthase (COASY), C19orf12, WDR45 and DCAF17 (C2orf37). These genes are involved in seemingly unrelated cellular pathways, such as lipid metabolism, Coenzyme A synthesis and autophagy. A greater understanding of the cellular pathways that link these genes and the disease mechanisms leading to iron dyshomeostasis is needed. Additionally, the major overlap seen between NBIA and more common neurodegenerative diseases may highlight conserved disease processes. In this review, we will discuss clinical and pathological findings for each NBIA-related gene, discuss proposed disease mechanisms such as mitochondrial health, oxidative damage, autophagy/mitophagy and iron homeostasis, and speculate the potential overlap between NBIA subtypes.

Neuropathology of Beta-propeller protein associated neurodegeneration (BPAN): a new tauopathy.

INTRODUCTION: Beta-propeller protein associated neurodegeneration (BPAN) is associated with mutations in the WD repeat domain 45 (WDR45) gene on chromosome Xp11 resulting in reduced autophagic flux. This study describes the clinical and neuropathological features of a female 51 year old BPAN case. The clinical history includes learning disability and progressive gait abnormalities since childhood followed by progressive dystonic features in young adulthood. Brain imaging revealed generalised brain atrophy and bilateral mineralisation of the globus pallidus and substantia nigra. RESULTS: The major pathological findings were observed in the substantia nigra with excess iron deposition, gliosis, axonal swellings and severe neuronal loss. Iron deposition was also observed in the globus pallidus. There was extensive hyperphosphorylated-tau deposition in the form of neurofibrillary tangles, pre-tangles and neuropil threads. Furthermore, histological studies and immunoblotting confirmed a mixed Alzheimer type 3-and 4-repeat tau pathology. Microtubule-associated protein 1A/1B-light chain 3 (LC3) immunoblotting of brain homogenates indicated autophagic activity and may support the role of WDR45 in autophagy. CONCLUSIONS: The widespread Alzheimer-type tau pathology in this disease indicates that this should be considered as a tauopathy and adds further support to the proposal that impaired autophagy may have a role in tauopathies.

Pantothenate kinase-associated neurodegeneration is not a synucleinopathy.

AIMS: Mutations in the pantothenate kinase 2 gene (PANK2) are responsible for the most common type of neurodegeneration with brain iron accumulation (NBIA), known as pantothenate kinase-associated neurodegeneration (PKAN). Historically, NBIA is considered a synucleinopathy with numerous reports of NBIA cases with Lewy bodies and Lewy neurites and some cases reporting additional abnormal tau accumulation. However, clinicopathological correlations in genetically proven PKAN cases are rare. We describe the clinical, genetic and neuropathological features of three unrelated PKAN cases. METHODS: All three cases were genetically screened for the PANK2 gene mutations using standard Sanger polymerase chain reaction sequencing. A detailed neuropathological assessment of the three cases was performed using histochemical and immunohistochemical preparations. RESULTS: All cases had classical axonal swellings and Perls' positive iron deposition in the basal ganglia. In contrast to neuroaxonal dystrophies due to mutation of the phospholipase A2, group VI (PLA2G6) gene, in which Lewy body pathology is widespread, no α-synuclein accumulation was detected in any of our PKAN cases. In one case (20-year-old male) there was significant tau pathology comprising neurofibrillary tangles and neuropil threads, with very subtle tau pathology in another case. CONCLUSIONS: These findings indicate that PKAN is not a synucleinopathy and, hence the cellular pathways implicated in this disease are unlikely to be relevant for the pathomechanism of Lewy body disorders.

Review: genetics and neuropathology of primary pure dystonia.

Neuropathology has been the key to understanding the aetiology of many neurological disorders such as Alzheimer's disease, Parkinson's disease, frontotemporal degeneration and cerebellar ataxias. Dystonia shares many clinical features with these conditions but research in general, has been unrewarding in providing information on disease processes. Neuropathological studies are few in number and only limited morphological abnormalities have been described. In the genetic literature, dystonia loci are represented as DYT and are assigned ascending numerals chronologically as they are identified. This review will concentrate on the neuropathology of primary pure dystonia, focusing on DYT1 and DYT6 and the correlation between clinical and genetic findings. Research in this area is incomplete and confounded by the rarity of post mortem brain tissue. However, recent findings, indicating a direct interaction between the torsinA (TOR1A) gene responsible for DYT1 and the thanatos-associated domain-containing apoptosis-associated protein 1 (THAP1) gene responsible for DYT6, have important implications in understanding these two entities and also for other members of this group of disorders.

Frequency of mutations in the genes associated with hereditary sensory and autonomic neuropathy in a UK cohort.

The hereditary sensory and autonomic neuropathies (HSAN, also known as the hereditary sensory neuropathies) are a clinically and genetically heterogeneous group of disorders, characterised by a progressive sensory neuropathy often complicated by ulcers and amputations, with variable motor and autonomic involvement. To date, mutations in twelve genes have been identified as causing HSAN. To study the frequency of mutations in these genes and the associated phenotypes, we screened 140 index patients in our inherited neuropathy cohort with a clinical diagnosis of HSAN for mutations in the coding regions of SPTLC1, RAB7, WNK1/HSN2, FAM134B, NTRK1 (TRKA) and NGFB. We identified 25 index patients with mutations in six genes associated with HSAN (SPTLC1, RAB7, WNK1/HSN2, FAM134B, NTRK1 and NGFB); 20 of which appear to be pathogenic giving an overall mutation frequency of 14.3%. Mutations in the known genes for HSAN are rare suggesting that further HSAN genes are yet to be identified. The p.Cys133Trp mutation in SPTLC1 is the most common cause of HSAN in the UK population and should be screened first in all patients with sporadic or autosomal dominant HSAN.

Genetic screening of Greek patients with Huntington's disease phenocopies identifies an SCA8 expansion.

Huntington's disease (HD) is an autosomal dominant disorder characterized by a triad of chorea, psychiatric disturbance and cognitive decline. Around 1% of patients with HD-like symptoms lack the causative HD expansion and are considered HD phenocopies. Genetic diseases that can present as HD phenocopies include HD-like syndromes such as HDL1, HDL2 and HDL4 (SCA17), some spinocerebellar ataxias (SCAs) and dentatorubral-pallidoluysian atrophy (DRPLA). In this study we screened a cohort of 21 Greek patients with HD phenocopy syndromes formutations causing HDL2, SCA17, SCA1, SCA2, SCA3,SCA8, SCA12 and DRPLA. Fifteen patients (71%) had a positive family history. We identified one patient (4.8% of the total cohort) with an expansion of 81 combined CTA/CTG repeats at the SCA8 locus. This falls within what is believed to be the high-penetrance allele range. In addition to the classic HD triad, the patient had features of dystonia and oculomotor apraxia. There were no cases of HDL2, SCA17, SCA1, SCA2, SCA3, SCA12 or DRPLA. Given the controversy surrounding the SCA8 expansion, the present finding may be incidental. However, if pathogenic, it broadens the phenotype that may be associated with SCA8 expansions. The absence of any other mutations in our cohort is not surprising, given the low probability of reaching a genetic diagnosis in HD phenocopy patients.

Neuroimaging features of neurodegeneration with brain iron accumulation.

NBIA characterizes a class of neurodegenerative diseases that feature a prominent extrapyramidal movement disorder, intellectual deterioration, and a characteristic deposition of iron in the basal ganglia. The diagnosis of NBIA is made on the basis of the combination of representative clinical features along with MR imaging evidence of iron accumulation. In many cases, confirmatory molecular genetic testing is now available as well. A number of new subtypes of NBIA have recently been described, with distinct neuroradiologic and clinical features. This article outlines the known subtypes of NBIA, delineates their clinical and radiographic features, and suggests an algorithm for evaluation.

The neuropathology, pathophysiology and genetics of multiple system atrophy.

Multiple system atrophy (MSA) is an unrelenting, sporadic, adult-onset, neurodegenerative disease of unknown aetiology. Its clinically progressive course is characterized by a variable combination of parkinsonism, cerebellar ataxia and/or autonomic dysfunction. Neuropathological examination often reveals gross abnormalities of the striatonigral and/or olivopontocerebellar systems, which upon microscopic examination are associated with severe neuronal loss, gliosis, myelin pallor and axonal degeneration. MSA is a member of a diverse group of neurodegenerative disorders termed α-synucleinopathies, due to the presence of abnormal α-synuclein positive cytoplasmic inclusions in oligodendrocytes, termed glial cytoplasmic inclusions. These are the hallmark neuropathological lesion of MSA and are thought to play a central role in the pathogenesis of the disease. In this review, neuropathological features of MSA are described in detail, along with recent advances in the pathophysiology and genetics of the disease. Our current knowledge of the expression and accumulation of α-synuclein, and efforts to model the disease in vitro and in vivo, are emphasized in this paper and have helped formulate a working hypothesis for the pathogenesis of MSA.