Genome sequence analyses identify novel risk loci for multiple system atrophy

Multiple system atrophy (MSA) is an adult-onset, sporadic synucleinopathy characterized by parkinsonism, cerebellar ataxia, and dysautonomia. The genetic architecture of MSA is poorly understood, and treatments are limited to supportive measures. Here, we performed a comprehensive analysis of whole genome sequence data from 888 European-ancestry MSA cases and 7,128 controls to systematically investigate the genetic underpinnings of this understudied neurodegenerative disease. We identified four significantly associated risk loci using a genome-wide association study approach. Transcriptome-wide association analyses prioritized USP38-DT, KCTD7, and lnc-KCTD7-2 as novel susceptibility genes for MSA within these loci, and single-nucleus RNA sequence analysis found that the associated variants acted as cis-expression quantitative trait loci for multiple genes across neuronal and glial cell types. In conclusion, this study highlights the role of genetic determinants in the pathogenesis of MSA, and the publicly available data from this study represent a valuable resource for investigating synucleinopathies.

Detection of mosaic and population-level structural variants with Sniffles2

Calling structural variations (SVs) is technically challenging, but using long reads remains the most accurate way to identify complex genomic alterations. Here we present Sniffles2, which improves over current methods by implementing a repeat aware clustering coupled with a fast consensus sequence and coverage-adaptive filtering. Sniffles2 is 11.8 times faster and 29% more accurate than state-of-the-art SV callers across different coverages (5-50×), sequencing technologies (ONT and HiFi) and SV types. Furthermore, Sniffles2 solves the problem of family-level to population-level SV calling to produce fully genotyped VCF files. Across 11 probands, we accurately identified causative SVs around MECP2, including highly complex alleles with three overlapping SVs. Sniffles2 also enables the detection of mosaic SVs in bulk long-read data. As a result, we identified multiple mosaic SVs in brain tissue from a patient with multiple system atrophy. The identified SV showed a remarkable diversity within the cingulate cortex, impacting both genes involved in neuron function and repetitive elements.

Single-cell somatic copy number variants in brain using different amplification methods and reference genomes

The presence of somatic mutations, including copy number variants (CNVs), in the brain is well recognized. Comprehensive study requires single-cell whole genome amplification, with several methods available, prior to sequencing. We compared PicoPLEX with two recent adaptations of multiple displacement amplification (MDA): primary template-directed amplification (PTA) and droplet MDA, across 93 human brain cortical nuclei. We demonstrated different properties for each, with PTA providing the broadest amplification, PicoPLEX the most even, and distinct chimeric profiles. Furthermore, we performed CNV calling on two brains with multiple system atrophy and one control brain using different reference genomes. We found that 38% of brain cells have at least one Mb-scale CNV, with some supported by bulk sequencing or single-cells from other brain regions. Our study highlights the importance of selecting whole genome amplification method and reference genome for CNV calling, while supporting the existence of somatic CNVs in healthy and diseased human brain.

Phenotypic effect of GBA1 variants in individuals with and without Parkinson's disease: The RAPSODI study

BACKGROUND

Variants in the GBA1 gene cause the lysosomal storage disorder Gaucher disease (GD). They are also risk factors for Parkinson's disease (PD), and modify the expression of the PD phenotype. The penetrance of GBA1 variants in PD is incomplete, and the ability to determine who among GBA1 variant carriers are at higher risk of developing PD, would represent an advantage for prognostic and trial design purposes.

OBJECTIVES

To compare the motor and non-motor phenotype of GBA1 carriers and non-carriers.

METHODS

We present the cross-sectional results of the baseline assessment from the RAPSODI study, an online assessment tool for PD patients and GBA1 variant carriers. The assessment includes clinically validated questionnaires, a tap-test, the University of Pennsyllvania Smell Identification Test and cognitive tests. Additional, homogeneous data from the PREDICT-PD cohort were included.

RESULTS

A total of 379 participants completed all parts of the RAPSODI assessment (89 GBA1-negative controls, 169 GBA1-negative PD, 47 GBA1-positive PD, 47 non-affected GBA1 carriers, 27 GD). Eighty-six participants were recruited through PREDICT-PD (43 non-affected GBA1 carriers and 43 GBA1-negative controls). GBA1-positive PD patients showed worse performance in visual cognitive tasks and olfaction compared to GBA1-negative PD patients. No differences were detected between non-affected GBA1 carriers carriers and GBA1-negative controls. No phenotypic differences were observed between any of the non-PD groups.

CONCLUSIONS

Our results support previous evidence that GBA1-positive PD has a specific phenotype with more severe non-motor symptoms. However, we did not reproduce previous findings of more frequent prodromal PD signs in non-affected GBA1 carriers.

Somatic SNCA Copy Number Variants in Multiple System Atrophy are Related to Pathology and Inclusions

BACKGROUND

Somatic α-synuclein (SNCA) copy number variants (CNVs, specifically gains) occur in multiple system atrophy (MSA) and Parkinson's disease brains.

OBJECTIVE

The aim was to compare somatic SNCA CNVs in MSA subtypes (striatonigral degeneration [SND] and olivopontocerebellar atrophy [OPCA]) and correlate with inclusions.

METHODS

We combined fluorescent in situ hybridization with immunofluorescence for α-synuclein and in some cases oligodendrocyte marker tubulin polymerization promoting protein (TPPP).

RESULTS

We analyzed one to three brain regions from 24 MSA cases (13 SND, 11 OPCA). In a region preferentially affected in one subtype (putamen in SND, cerebellum in OPCA), mosaicism was higher in that subtype, and cells with CNVs were 4.2 times more likely to have inclusions. In the substantia nigra, nonpigmented cells with CNVs and TPPP were about six times more likely to have inclusions.

CONCLUSIONS

The correlation between SNCA CNVs and pathology (at a regional level) and inclusions (at a single-cell level) suggests a role for somatic SNCA CNVs in MSA pathogenesis. © 2022 The Authors. Movement Disorders published by Wiley Periodicals LLC on behalf of International Parkinson and Movement Disorder Society.

Somatic CNV Detection by Single-Cell Whole-Genome Sequencing in Postmortem Human Brain

The evidence for a role of somatic mutations, including copy-number variants (CNVs), in neurodegeneration has increased in the last decade. However, the understanding of the types and origins of these mutations, and their exact contributions to disease onset and progression, is still in its infancy. The use of single-cell (or nuclear) whole-genome sequencing (scWGS) has emerged as a powerful tool to answer these questions. In the present chapter, we provide laboratory and bioinformatic protocols used successfully in our lab to detect megabase-scale CNVs in single cells from multiple system atrophy (MSA) human postmortem brains, using immunolabeling prior to selection of nuclei for whole-genome amplification (WGA). We also present an unpublished comparison of scWGS generated from the same control substantia nigra (SN) sample, using the latest versions of popular WGA chemistries, MDA and PicoPLEX. We have used this protocol to focus on brain cell types most relevant to synucleinopathies (dopaminergic [DA] neurons in Parkinson's disease [PD] and oligodendrocytes in MSA), but it can be applied to any tissue and/or cell type with appropriate markers.

Comprehensive short and long read sequencing analysis for the Gaucher and Parkinson's disease-associated GBA gene

GBA variants carriers are at increased risk of Parkinson’s disease (PD) and Lewy body dementia (LBD). The presence of pseudogene GBAP1 predisposes to structural variants, complicating genetic analysis. We present two methods to resolve recombinant alleles and other variants in GBA: Gauchian, a tool for short-read, whole-genome sequencing data analysis, and Oxford Nanopore sequencing after PCR enrichment. Both methods were concordant for 42 samples carrying a range of recombinants and GBAP1-related mutations, and Gauchian outperformed the GATK Best Practices pipeline. Applying Gauchian to sequencing of over 10,000 individuals shows that copy number variants (CNVs) spanning GBAP1 are relatively common in Africans. CNV frequencies in PD and LBD are similar to controls. Gains may coexist with other mutations in patients, and a modifying effect cannot be excluded. Gauchian detects more GBA variants in LBD than PD, especially severe ones. These findings highlight the importance of accurate GBA analysis in these patients.

Two methods fully resolve the GBA gene: Gauchian, a tool for short-read, whole-genome sequencing data analysis, and Oxford Nanopore sequencing after PCR enrichment. The approach improves our understanding of the relationship between GBA, Gaucher disease and Parkinson disease.

Intronic Haplotypes in the GBA Gene Do Not Predict Age at Diagnosis of Parkinson's Disease

BACKGROUND

GBA mutations are a common risk factor for Parkinson's disease (PD). A recent study has suggested that GBA haplotypes, identified by intronic variants, can affect age at diagnosis of PD.

OBJECTIVES

In this study, we assess this hypothesis using long reads across a large cohort and the publicly available Accelerating Medicines Partnership-Parkinson's Disease (AMP-PD) cohort.

METHODS

We recruited a PD cohort through the Remote Assessment of Parkinsonism Supporting Ongoing Development of Interventions in Gaucher Disease study (RAPSODI) and sequenced GBA using Oxford Nanopore technology. Genetic and clinical data on the full AMP-PD cohort were obtained from the online portal of the consortium.

RESULTS

A total of 1417 participants were analyzed. There was no significant difference in age at PD diagnosis between the two main haplotypes of the GBA gene.

CONCLUSIONS

GBA haplotypes do not affect age at diagnosis of PD in the two independent cohorts studied. © 2021 The Authors. Movement Disorders published by Wiley Periodicals LLC on behalf of International Parkinson and Movement Disorder Society.

Complex mosaic structural variations in human fetal brains

Somatic mosaicism, manifesting as single nucleotide variants (SNVs), mobile element insertions, and structural changes in the DNA, is a common phenomenon in human brain cells, with potential functional consequences. Using a clonal approach, we previously detected 200-400 mosaic SNVs per cell in three human fetal brains (15-21 wk postconception). However, structural variation in the human fetal brain has not yet been investigated. Here, we discover and validate four mosaic structural variants (SVs) in the same brains and resolve their precise breakpoints. The SVs were of kilobase scale and complex, consisting of deletion(s) and rearranged genomic fragments, which sometimes originated from different chromosomes. Sequences at the breakpoints of these rearrangements had microhomologies, suggesting their origin from replication errors. One SV was found in two clones, and we timed its origin to ∼14 wk postconception. No large scale mosaic copy number variants (CNVs) were detectable in normal fetal human brains, suggesting that previously reported megabase-scale CNVs in neurons arise at later stages of development. By reanalysis of public single nuclei data from adult brain neurons, we detected an extrachromosomal circular DNA event. Our study reveals the existence of mosaic SVs in the developing human brain, likely arising from cell proliferation during mid-neurogenesis. Although relatively rare compared to SNVs and present in ∼10% of neurons, SVs in developing human brain affect a comparable number of bases in the genome (∼6200 vs. ∼4000 bp), implying that they may have similar functional consequences.

Investigation of Somatic Mutations in Human Brains Targeting Genes Associated With Parkinson's Disease

Background: Somatic single nucleotide variant (SNV) mutations occur in neurons but their role in synucleinopathies is unknown.

Aim: We aimed to identify disease-relevant low-level somatic SNVs in brains from sporadic patients with synucleinopathies and a monozygotic twin carrying LRRK2 G2019S, whose penetrance could be explained by somatic variation.

Methods and Results: We included different brain regions from 26 Parkinson's disease (PD), one Incidental Lewy body, three multiple system atrophy cases, and 12 controls. The whole SNCA locus and exons of other genes associated with PD and neurodegeneration were deeply sequenced using molecular barcodes to improve accuracy. We selected 21 variants at 0.33–5% allele frequencies for validation using accurate methods for somatic variant detection.

Conclusions: We could not detect disease-relevant somatic SNVs, however we cannot exclude their presence at earlier stages of degeneration. Our results support that coding somatic SNVs in neurodegeneration are rare, but other types of somatic variants may hold pathological consequences in synucleinopathies.

Somatic mutations in neurodegeneration: An update

Mosaicism, the presence of genomic differences between cells due to post-zygotic somatic mutations, is widespread in the human body, including within the brain. A role for this in neurodegenerative diseases has long been hypothesised, and technical developments are now allowing the question to be addressed in detail. The rapidly accumulating evidence is discussed in this review, with a focus on recent developments. Somatic mutations of numerous types may occur, including single nucleotide variants (SNVs), copy number variants (CNVs), and retrotransposon insertions. They could act as initiators or risk factors, especially if they arise in development, although they could also result from the disease process, potentially contributing to progression. In common sporadic neurodegenerative disorders, relevant mutations have been reported in synucleinopathies, comprising somatic gains of SNCA in Parkinson's disease and multiple system atrophy, and in Alzheimer's disease, where a novel recombination mechanism leading to somatic variants of APP, as well as an excess of somatic SNVs affecting tau phosphorylation, have been reported. In Mendelian repeat expansion disorders, mosaicism due to somatic instability, first detected 25 years ago, has come to the forefront. Brain somatic SNVs occur in DNA repair disorders, and there is evidence for a role of several ALS genes in DNA repair. While numerous challenges, and need for further validation, remain, this new, or perhaps rediscovered, area of research has the potential to transform our understanding of neurodegeneration.

A crowdsourced set of curated structural variants for the human genome

A high quality benchmark for small variants encompassing 88 to 90% of the reference genome has been developed for seven Genome in a Bottle (GIAB) reference samples. However a reliable benchmark for large indels and structural variants (SVs) is more challenging. In this study, we manually curated 1235 SVs, which can ultimately be used to evaluate SV callers or train machine learning models. We developed a crowdsourcing app-SVCurator-to help GIAB curators manually review large indels and SVs within the human genome, and report their genotype and size accuracy. SVCurator displays images from short, long, and linked read sequencing data from the GIAB Ashkenazi Jewish Trio son [NIST RM 8391/HG002]. We asked curators to assign labels describing SV type (deletion or insertion), size accuracy, and genotype for 1235 putative insertions and deletions sampled from different size bins between 20 and 892,149 bp. 'Expert' curators were 93% concordant with each other, and 37 of the 61 curators had at least 78% concordance with a set of 'expert' curators. The curators were least concordant for complex SVs and SVs that had inaccurate breakpoints or size predictions. After filtering events with low concordance among curators, we produced high confidence labels for 935 events. The SVCurator crowdsourced labels were 94.5% concordant with the heuristic-based draft benchmark SV callset from GIAB. We found that curators can successfully evaluate putative SVs when given evidence from multiple sequencing technologies.

Investigation of somatic CNVs in brains of synucleinopathy cases using targeted SNCA analysis and single cell sequencing

Synucleinopathies are mostly sporadic neurodegenerative disorders of partly unexplained aetiology, and include Parkinson's disease (PD) and multiple system atrophy (MSA). We have further investigated our recent finding of somatic SNCA (α-synuclein) copy number variants (CNVs, specifically gains) in synucleinopathies, using Fluorescent in-situ Hybridisation for SNCA, and single-cell whole genome sequencing for the first time in a synucleinopathy. In the cingulate cortex, mosaicism levels for SNCA gains were higher in MSA and PD than controls in neurons (> 2% in both diseases), and for MSA also in non-neurons. In MSA substantia nigra (SN), we noted SNCA gains in > 3% of dopaminergic (DA) neurons (identified by neuromelanin) and neuromelanin-negative cells, including olig2-positive oligodendroglia. Cells with CNVs were more likely to have α-synuclein inclusions, in a pattern corresponding to cell categories mostly relevant to the disease: DA neurons in Lewy-body cases, and other cells in the striatonigral degeneration-dominant MSA variant (MSA-SND). Higher mosaicism levels in SN neuromelanin-negative cells may correlate with younger onset in typical MSA-SND, and in cingulate neurons with younger death in PD. Larger sample sizes will, however, be required to confirm these putative findings. We obtained genome-wide somatic CNV profiles from 169 cells from the substantia nigra of two MSA cases, and pons and putamen of one. These showed somatic CNVs in ~ 30% of cells, with clonality and origins in segmental duplications for some. CNVs had distinct profiles based on cell type, with neurons having a mix of gains and losses, and other cells having almost exclusively gains, although control data sets will be required to determine possible disease relevance. We propose that somatic SNCA CNVs may contribute to the aetiology and pathogenesis of synucleinopathies, and that genome-wide somatic CNVs in MSA brain merit further study.

Evolution and clustering of prodromal parkinsonian features in GBA1 carriers

Background

Five to 25% of patients with PD carry glucocerebrosidase gene mutations, and 10% to 30% of glucocerebrosidase carriers will develop PD by age 80. Stratification of PD risk in glucocerebrosidase carriers provides an opportunity to target disease‐modifying therapies.

Objective

Cross‐sectional and longitudinal survey of prodromal PD signs among glucocerebrosidase carriers.

Design

Prospective assessment of 82 glucocerebrosidase mutation carriers and 35 controls over 4 to 5 years for prodromal clinical PD features.

Results

At all time points, olfactory (measured using University of Pennsylvania Smell Identification Test) and cognitive (Montreal Cognitive Assessment) function and the International Parkinson and Movement Disorder Society UPDRS parts II and III scores were significantly worse amongst glucocerebrosidase mutation carriers. Progression to microsmia (odds ratio: 8.5; 95% confidence interval: 2.6–28.2; P < 0.05) and mild cognitive impairment (odds ratio: 4.2; 95% confidence interval: 1.1–16.6; P < 0.05) were more rapid compared to controls. Those with worse olfaction also had worse cognition (OR, 1.5; 95% CI: 0.0–2.8; P < 0.05) and depression (OR, 1.3; 95% CI: 0.6–2.8; P < 0.05). No participants reached the MDS prodromal PD diagnostic criteria before PD diagnosis. One participant developed PD. He did not fulfill the International Parkinson and Movement Disorder Society prodromal PD criteria before diagnosis.

Conclusion

Assessment of individual and clustered PD prodromal features may serve as a useful tool to identify high‐risk subjects for conversion to PD. As a result of the low conversion rate in our glucocerebrosidase mutation carriers to date, prospective validation is needed in larger cohorts to establish the profile of these features in PD convertors. © 2019 The Authors. Movement Disorders published by Wiley Periodicals, Inc. on behalf of International Parkinson and Movement Disorder Society.

The Interaction of Genetic Mutations in PARK2 and FA2H Causes a Novel Phenotype in a Case of Childhood-Onset Movement Disorder

Mutations in the PARK2 gene have been implicated in the pathogenesis of early-onset Parkinson's disease. We present a case of movement disorder in a 4-year-old child from consanguineous parents and with a family history of Dopamine responsive dystonia, who was diagnosed with early-onset Parkinson's disease based on initial identification of a pathogenic PARK2 mutation. However, the evolution of the child's clinical picture was unusually rapid, with a preponderance of pyramidal rather than extrapyramidal symptoms, leading to re-investigation of the case with further imaging and genetic sequencing. Interestingly, a second homozygous mutation in the FA2H gene, implicated in Hereditary spastic paraplegia, was revealed, appearing to have contributed to the novel phenotype observed, and highlighting a potential interaction between the two mutated genes.

Evaluation of the detection of GBA missense mutations and other variants using the Oxford Nanopore MinION

BACKGROUND

Mutations in GBA cause Gaucher disease when biallelic and are strong risk factors for Parkinson's disease when heterozygous. GBA analysis is complicated by the nearby pseudogene. We aimed to design and validate a method for sequencing GBA using long reads.

METHODS

We sequenced GBA on the Oxford Nanopore MinION as an 8.9 kb amplicon from 102 individuals, including patients with Parkinson's and Gaucher diseases. We used NanoOK for quality metrics, NGMLR to align data (after comparing with GraphMap), Nanopolish and Sniffles to call variants, and WhatsHap for phasing.

RESULTS

We detected all known missense mutations in these samples, including the common p.N409S (N370S) and p.L483P (L444P) in multiple samples, and nine rarer ones, as well as a splicing and a truncating mutation, and intronic SNPs. We demonstrated the ability to phase mutations, confirm compound heterozygosity, and assign haplotypes. We also detected two known risk variants in some Parkinson's patients. Rare false positives were easily identified and filtered, with the Nanopolish quality score adjusted for the number of reads a very robust discriminator. In two individuals carrying a recombinant allele, we were able to detect and fully define it in one carrier, where it included a 55-base pair deletion, but not in another one, suggesting a limitation of the PCR enrichment method. Missense mutations were detected at the correct zygosity, except for the case where the RecNciI one was missed.

CONCLUSION

The Oxford Nanopore MinION can detect missense mutations and an exonic deletion in this difficult gene, with the added advantages of phasing and intronic analysis. It can be used as an efficient research tool, but additional work is required to exclude all recombinants.

Copy number variation of LINGO1 in familial dystonic tremor

Objective

To elucidate the genetic cause of a large 5 generation South Indian family with multiple individuals with predominantly an upper limb postural tremor and posturing in keeping with another form of tremor, namely, dystonic tremor.

Methods

Whole-genome single nucleotide polymorphism (SNP) microarray analysis was undertaken to look for copy number variants in the affected individuals.

Results

Whole-genome SNP microarray studies identified a tandem duplicated genomic segment of chromosome 15q24 present in all affected family members. Whole-genome sequencing demonstrated that it comprised a ∼550-kb tandem duplication encompassing the entire LINGO1 gene.

Conclusions

The identification of a genomic duplication as the likely molecular cause of this condition, resulting in an additional LINGO1 gene copy in affected cases, adds further support for a causal role of this gene in tremor disorders and implicates increased expression levels of LINGO1 as a potential pathogenic mechanism.

Review: Somatic mutations in neurodegeneration

Somatic mutations are postzygotic mutations which may lead to mosaicism, the presence of cells with genetic differences in an organism. Their role in cancer is well established, but detailed investigation in health and other diseases has only been recently possible. This has been empowered by the improvements of sequencing techniques, including single-cell sequencing, which can still be error-prone but is rapidly improving. Mosaicism appears relatively common in the human body, including the normal brain, probably arising in early development, but also potentially during ageing. In this review, we first discuss theoretical considerations and current evidence relevant to somatic mutations in the brain. We present a framework to explain how they may be integrated with current views on neurodegeneration, focusing mainly on sporadic late-onset neurodegenerative diseases (Parkinson's disease, Alzheimer's disease and amyotrophic lateral sclerosis). We review the relevant studies so far, with the first evidence emerging in Alzheimer's in particular. We also discuss the role of mosaicism in inherited neurodegenerative disorders, particularly somatic instability of tandem repeats. We summarize existing views and data to present a model whereby the time of origin and spatial distribution of relevant somatic mutations, combined with any additional risk factors, may partly determine the development and onset age of sporadic neurodegenerative diseases.

α-Synuclein structural features inhibit harmful polyunsaturated fatty acid oxidation, suggesting roles in neuroprotection

α-Synuclein (aS) is a protein abundant in presynaptic nerve terminals in Parkinson disease (PD) and is a major component of intracellular Lewy bodies, the pathological hallmark of neurodegenerative disorders such as PD. Accordingly, the relationships between aS structure, its interaction with lipids, and its involvement in neurodegeneration have attracted great interest. Previously, we reported on the interaction of aS with brain polyunsaturated fatty acids, in particular docosahexaenoic acid (DHA). aS acquires an α-helical secondary structure in the presence of DHA and, in turn, affects DHA structural and aggregative properties. Moreover, aS forms a covalent adduct with DHA. Here, we provide evidence that His-50 is the main site of this covalent modification. To better understand the role of His-50, we analyzed the effect of DHA on aS-derived species: a naturally occurring variant, H50Q; an oxidized aS in which all methionines are sulfoxides (aS4ox); a fully lysine-alkylated aS (acetyl-aS); and aS fibrils, testing their ability to be chemically modified by DHA. We show, by mass spectrometry and spectroscopic techniques, that H50Q and aS4ox are modified by DHA, whereas acetyl-aS is not. We correlated this modification with aS structural features, and we suggest a possible functional role of aS in sequestering the early peroxidation products of fatty acids, thereby reducing the level of highly reactive lipid species. Finally, we show that fibrillar aS loses almost 80% of its scavenging activity, thus lacking a potentially protective function. Our findings linking aS scavenging activity with brain lipid composition suggest a possible etiological mechanism in some neurodegenerative disorders.

Genetic and phenotypic characterization of complex hereditary spastic paraplegia

The hereditary spastic paraplegias are a heterogeneous group of degenerative disorders that are clinically classified as either pure with predominant lower limb spasticity, or complex where spastic paraplegia is complicated with additional neurological features, and are inherited in autosomal dominant, autosomal recessive or X-linked patterns. Genetic defects have been identified in over 40 different genes, with more than 70 loci in total. Complex recessive spastic paraplegias have in the past been frequently associated with mutations in SPG11 (spatacsin), ZFYVE26/SPG15 , SPG7 (paraplegin) and a handful of other rare genes, but many cases remain genetically undefined. The overlap with other neurodegenerative disorders has been implied in a small number of reports, but not in larger disease series. This deficiency has been largely due to the lack of suitable high throughput techniques to investigate the genetic basis of disease, but the recent availability of next generation sequencing can facilitate the identification of disease-causing mutations even in extremely heterogeneous disorders. We investigated a series of 97 index cases with complex spastic paraplegia referred to a tertiary referral neurology centre in London for diagnosis or management. The mean age of onset was 16 years (range 3 to 39). The SPG11 gene was first analysed, revealing homozygous or compound heterozygous mutations in 30/97 (30.9%) of probands, the largest SPG11 series reported to date, and by far the most common cause of complex spastic paraplegia in the UK, with severe and progressive clinical features and other neurological manifestations, linked with magnetic resonance imaging defects. Given the high frequency of SPG11 mutations, we studied the autophagic response to starvation in eight affected SPG11 cases and control fibroblast cell lines, but in our restricted study we did not observe correlations between disease status and autophagic or lysosomal markers. In the remaining cases, next generation sequencing was carried out revealing variants in a number of other known complex spastic paraplegia genes, including five in SPG7 (5/97), four in FA2H (also known as SPG35 ) (4/97) and two in ZFYVE26 / SPG15 . Variants were identified in genes usually associated with pure spastic paraplegia and also in the Parkinson’s disease-associated gene ATP13A2 , neuronal ceroid lipofuscinosis gene TPP1 and the hereditary motor and sensory neuropathy DNMT1 gene, highlighting the genetic heterogeneity of spastic paraplegia. No plausible genetic cause was identified in 51% of probands, likely indicating the existence of as yet unidentified genes.

A large Indian family with rearrangement of chromosome 4p16 and 3p26.3 and divergent clinical presentations

Background

The deletion of the chromosome 4p16.3 Wolf-Hirschhorn syndrome critical region (WHSCR-2) typically results in a characteristic facial appearance, varying intellectual disability, stereotypies and prenatal onset of growth retardation, while gains of the same chromosomal region result in a more variable degree of intellectual deficit and dysmorphism. Similarly the phenotype of individuals with terminal deletions of distal chromosome 3p (3p deletion syndrome) varies from mild to severe intellectual deficit, micro- and trigonocephaly, and a distinct facial appearance.

Methods and results

We investigated a large Indian five-generation pedigree with ten affected family members in which chromosomal microarray and fluorescence in situ hybridization analyses disclosed a complex rearrangement involving chromosomal subregions 4p16.1 and 3p26.3 resulting in a 4p16.1 deletion and 3p26.3 microduplication in three individuals, and a 4p16.1 duplication and 3p26.3 microdeletion in seven individuals. A typical clinical presentation of WHS was observed in all three cases with 4p16.1 deletion and 3p26.3 microduplication. Individuals with a 4p16.1 duplication and 3p26.3 microdeletion demonstrated a range of clinical features including typical 3p microdeletion or 4p partial trisomy syndrome to more severe neurodevelopmental delay with distinct dysmorphic features.

Conclusion

We present the largest pedigree with complex t(4p;3p) chromosomal rearrangements and diverse clinical outcomes including Wolf Hirschorn-, 3p deletion-, and 4p duplication syndrome amongst affected individuals.

Electronic supplementary material

The online version of this article (doi:10.1186/s12881-015-0251-5) contains supplementary material, which is available to authorized users.

Distinct clinical and neuropathological features of G51D SNCA mutation cases compared with SNCA duplication and H50Q mutation

BACKGROUND

We and others have described the neurodegenerative disorder caused by G51D SNCA mutation which shares characteristics of Parkinson's disease (PD) and multiple system atrophy (MSA). The objective of this investigation was to extend the description of the clinical and neuropathological hallmarks of G51D mutant SNCA-associated disease by the study of two additional cases from a further G51D SNCA kindred and to compare the features of this group with a SNCA duplication case and a H50Q SNCA mutation case.

RESULTS

All three G51D patients were clinically characterised by parkinsonism, dementia, visual hallucinations, autonomic dysfunction and pyramidal signs with variable age at disease onset and levodopa response. The H50Q SNCA mutation case had a clinical picture that mimicked late-onset idiopathic PD with a good and sustained levodopa response. The SNCA duplication case presented with a clinical phenotype of frontotemporal dementia with marked behavioural changes, pyramidal signs, postural hypotension and transiently levodopa responsive parkinsonism. Detailed post-mortem neuropathological analysis was performed in all cases. All three G51D cases had abundant α-synuclein pathology with characteristics of both PD and MSA. These included widespread cortical and subcortical neuronal α-synuclein inclusions together with small numbers of inclusions resembling glial cytoplasmic inclusions (GCIs) in oligodendrocytes. In contrast the H50Q and SNCA duplication cases, had α-synuclein pathology resembling idiopathic PD without GCIs. Phosphorylated α-synuclein was present in all inclusions types in G51D cases but was more restricted in SNCA duplication and H50Q mutation. Inclusions were also immunoreactive for the 5G4 antibody indicating their highly aggregated and likely fibrillar state.

CONCLUSIONS

Our characterisation of the clinical and neuropathological features of the present small series of G51D SNCA mutation cases should aid the recognition of this clinico-pathological entity. The neuropathological features of these cases consistently share characteristics of PD and MSA and are distinct from PD patients carrying the H50Q or SNCA duplication.

Evolution of prodromal clinical markers of Parkinson disease in a GBA mutation-positive cohort

IMPORTANCE

Numerically, the most important genetic risk factor for the development of Parkinson disease (PD) is the presence of a glucocerebrosidase gene (GBA) mutation.

OBJECTIVE

To evaluate longitudinally and clinically a GBA mutation-positive cohort and the evolution of the prodromal features of PD.

DESIGN, SETTING, AND PARTICIPANTS

Participants in a study of the etiology and prodrome of PD were reevaluated in this clinic-based 2-year follow-up report. Patients with type 1 Gaucher disease (GD) and heterozygous GBA mutation carriers were recruited in 2010 from the Lysosomal Storage Disorder Unit at the Royal Free Hospital, London, England. Thirty patients who previously received a diagnosis of type 1 GD, 28 heterozygous GBA mutation carriers, and 26 genetically unrelated controls were included. Exclusion criteria included a diagnosis of PD or dementia for both the patients with GD and the GBA mutation carriers and any existing neurological disease for the controls.

MAIN OUTCOMES AND MEASURES

Assessment was performed for clinical markers using standardized scales for hyposmia, rapid eye movement sleep behavior disorder, depression, autonomic dysfunction, cognitive function, and parkinsonian motor signs (using the Unified Parkinson's Disease Rating Scale motor subscale [UPDRS part III]).

RESULTS

Over 2 years, depression scores were significantly worse for heterozygous carriers (mean baseline, 0.65; mean follow-up, 2.88; P = .01), rapid eye movement sleep behavior disorder scores were significantly worse for patients with GD (mean baseline, 0.93; mean follow-up, 2.93; P < .001) and heterozygotes (mean baseline, 0.10; mean follow-up, 2.30; P < .001), and UPDRS part III scores were significantly worse for patients with GD (mean baseline, 4.29; mean follow-up, 7.82; P < .001) and heterozygotes (mean baseline, 1.97; mean follow-up, 4.50; P < .001). For controls, there was a small but significant deterioration in the UPDRS part II (activities of daily living) score (mean baseline, 0.00; mean follow-up, 0.58; P = .006). At 2 years, olfactory and cognitive assessment scores were lower in patients with GD and heterozygotes compared with controls, but they did not differ significantly from baseline. When the results from the patients with GD and the heterozygotes were combined, a significant deterioration from baseline was observed, as reflected in the Rapid Eye Movement Sleep Behaviour Disorder Questionnaire (mean baseline, 0.51; mean follow-up, 2.63; P < .001), Beck Depression Inventory (mean baseline, 1.72; mean follow-up, 4.44; P = .002), and UPDRS part II (mean baseline, 0.88; mean follow-up, 2.01; P < .001) and part III scores (mean baseline, 3.09; mean follow-up, 6.10; P < .001) (all P < .01), and at 2 years, significant differences in University of Pennsylvania Smell Identification Test, Unified Multiple System Atrophy Rating Scale, Mini-Mental State Examination, Montreal Cognitive Assessment, and UPDRS part II and part III scores were observed between patients with GD/heterozygotes and controls (all P < .05).

CONCLUSIONS AND RELEVANCE

This study indicates that, as a group, GBA mutation-positive individuals show a deterioration in clinical markers consistent with the prodrome of PD. Within this group of individual, 10% appear to be evolving at a more rapid rate.

The H50Q mutation induces a 10-fold decrease in the solubility of α-synuclein

The conversion of α-synuclein from its intrinsically disordered monomeric state into the fibrillar cross-β aggregates characteristically present in Lewy bodies is largely unknown. The investigation of α-synuclein variants causative of familial forms of Parkinson disease can provide unique insights into the conditions that promote or inhibit aggregate formation. It has been shown recently that a newly identified pathogenic mutation of α-synuclein, H50Q, aggregates faster than the wild-type. We investigate here its aggregation propensity by using a sequence-based prediction algorithm, NMR chemical shift analysis of secondary structure populations in the monomeric state, and determination of thermodynamic stability of the fibrils. Our data show that the H50Q mutation induces only a small increment in polyproline II structure around the site of the mutation and a slight increase in the overall aggregation propensity. We also find, however, that the H50Q mutation strongly stabilizes α-synuclein fibrils by 5.0 ± 1.0 kJ mol⁻¹, thus increasing the supersaturation of monomeric α-synuclein within the cell, and strongly favors its aggregation process. We further show that wild-type α-synuclein can decelerate the aggregation kinetics of the H50Q variant in a dose-dependent manner when coaggregating with it. These last findings suggest that the precise balance of α-synuclein synthesized from the wild-type and mutant alleles may influence the natural history and heterogeneous clinical phenotype of Parkinson disease.

A 6.4 Mb duplication of the α-synuclein locus causing frontotemporal dementia and Parkinsonism: phenotype-genotype correlations

IMPORTANCE

α-Synuclein (SNCA) locus duplications are associated with variable clinical features and reduced penetrance but the reasons underlying this variability are unknown.

OBJECTIVES

To report a novel family carrying a heterozygous 6.4 Mb duplication of the SNCA locus with an atypical clinical presentation strongly reminiscent of frontotemporal dementia and late-onset pallidopyramidal syndromes and study phenotype-genotype correlations in SNCA locus duplications.

DESIGN, SETTING, AND PARTICIPANTS

We report the clinical and neuropathologic features of a family carrying a 6.4 Mb duplication of the SNCA locus. To identify candidate disease modifiers, we completed a genetic analysis of the family and conducted statistical analysis on previously published cases carrying SNCA locus duplications using regression modeling with robust standard errors to account for clustering at the family level.

MAIN OUTCOMES AND MEASURES

We assessed whether length of the SNCA locus duplication influences disease penetrance and severity and whether extraduplication factors have a disease-modifying role.

RESULTS

We identified a large 6.4 Mb duplication of the SNCA locus in this family. Neuropathological analysis showed extensive α-synuclein pathology with minimal phospho-tau pathology. Genetic analysis showed an increased burden of Parkinson disease-related risk factors and the disease-predisposing H1/H1 microtubule-associated protein tau haplotype. Statistical analysis of previously published cases suggested there is a trend toward increasing disease severity and disease penetrance with increasing duplication size. The corresponding odds ratios from the univariable analyses were 1.17 (95% CI, 0.81-1.68) and 1.34 (95% CI, 0.78-2.31), respectively. Sex was significantly associated with both disease risk and severity; men compared with women had increased disease risk and severity and the corresponding odds ratios from the univariable analyses were 8.36 (95% CI, 1.97-35.42) and 5.55 (95% CI, 1.39-22.22), respectively.

CONCLUSIONS AND RELEVANCE

These findings further expand the phenotypic spectrum of SNCA locus duplications. Increased dosage of genes located within the duplicated region probably cannot increase disease risk and disease severity without the contribution of additional risk factors. Identification of disease modifiers accounting for the substantial phenotypic heterogeneity of patients with SNCA locus duplications could provide insight into molecular events involved in α-synuclein aggregation.

Extended phenotypic spectrum of KIF5A mutations: From spastic paraplegia to axonal neuropathy

OBJECTIVE

To establish the phenotypic spectrum of KIF5A mutations and to investigate whether KIF5A mutations cause axonal neuropathy associated with hereditary spastic paraplegia (HSP) or typical Charcot-Marie-Tooth disease type 2 (CMT2).

METHODS

KIF5A sequencing of the motor-domain coding exons was performed in 186 patients with the clinical diagnosis of HSP and in 215 patients with typical CMT2. Another 66 patients with HSP or CMT2 with pyramidal signs were sequenced for all exons of KIF5A by targeted resequencing. One additional patient was genetically diagnosed by whole-exome sequencing.

RESULTS

Five KIF5A mutations were identified in 6 unrelated patients: R204W and D232N were novel mutations; R204Q, R280C, and R280H have been previously reported. Three patients had CMT2 as the predominant and presenting phenotype; 2 of them also had pyramidal signs. The other 3 patients presented with HSP but also had significant axonal neuropathy or other additional features.

CONCLUSION

This is currently the largest study investigating KIF5A mutations. By combining next-generation sequencing and conventional sequencing, we confirm that KIF5A mutations can cause variable phenotypes ranging from HSP to CMT2. The identification of mutations in CMT2 broadens the phenotypic spectrum and underlines the importance of KIF5A mutations, which involve degeneration of both the central and peripheral nervous systems and should be tested in HSP and CMT2.

Visual short-term memory deficits associated with GBA mutation and Parkinson's disease

Individuals with mutation in the lysosomal enzyme glucocerebrosidase (GBA) gene are at significantly high risk of developing Parkinson’s disease with cognitive deficit. We examined whether visual short-term memory impairments, long associated with patients with Parkinson’s disease, are also present in GBA-positive individuals—both with and without Parkinson’s disease. Precision of visual working memory was measured using a serial order task in which participants observed four bars, each of a different colour and orientation, presented sequentially at screen centre. Afterwards, they were asked to adjust a coloured probe bar’s orientation to match the orientation of the bar of the same colour in the sequence. An additional attentional ‘filtering’ condition tested patients’ ability to selectively encode one of the four bars while ignoring the others. A sensorimotor task using the same stimuli controlled for perceptual and motor factors. There was a significant deficit in memory precision in GBA-positive individuals—with or without Parkinson’s disease—as well as GBA-negative patients with Parkinson’s disease, compared to healthy controls. Worst recall was observed in GBA-positive cases with Parkinson’s disease. Although all groups were impaired in visual short-term memory, there was a double dissociation between sources of error associated with GBA mutation and Parkinson’s disease. The deficit observed in GBA-positive individuals, regardless of whether they had Parkinson’s disease, was explained by a systematic increase in interference from features of other items in memory: misbinding errors. In contrast, impairments in patients with Parkinson’s disease, regardless of GBA status, was explained by increased random responses. Individuals who were GBA-positive and also had Parkinson’s disease suffered from both types of error, demonstrating the worst performance. These findings provide evidence for dissociable signature deficits within the domain of visual short-term memory associated with GBA mutation and with Parkinson’s disease. Identification of the specific pattern of cognitive impairment in GBA mutation versus Parkinson’s disease is potentially important as it might help to identify individuals at risk of developing Parkinson’s disease.

Analysis of Parkinson's disease brain-derived DNA for alpha-synuclein coding somatic mutations

Background

Although alpha-synuclein (SNCA) is crucial to the pathogenesis of Parkinson's disease (PD) and dementia with Lewy bodies (DLB), mutations in the gene appear to be rare. We have recently hypothesized that somatic mutations in early development could contribute to PD.

Methods

Expanding on our recent negative small study, we used high-resolution melting (HRM) analysis to screen SNCA coding exons for somatic point mutations in DNA from 539 PD and DLB cerebellar samples, with two additional regions (frontal cortex, substantia nigra) for 20 PD cases. We used artificial mosaics to determine sensitivity where possible.

Results

We did not detect any evidence of somatic coding mutations. Three cases were heterozygous for known silent polymorphisms. The protocol we used was sensitive enough to detect 5% to 10% mutant DNA.

Conclusion

Using DNA predominantly from cerebellum, but also from frontal cortex and substantia nigra (n = 20 each), we have not detected any somatic coding SNCA point mutations. © 2014 The Authors. Movement Disorders published by Wiley Periodicals, Inc. on behalf of International Parkinson and Movement Disorder Society.

Mutations in B4GALNT1 (GM2 synthase) underlie a new disorder of ganglioside biosynthesis

Glycosphingolipids are ubiquitous constituents of eukaryotic plasma membranes, and their sialylated derivatives, gangliosides, are the major class of glycoconjugates expressed by neurons. Deficiencies in their catabolic pathways give rise to a large and well-studied group of inherited disorders, the lysosomal storage diseases. Although many glycosphingolipid catabolic defects have been defined, only one proven inherited disease arising from a defect in ganglioside biosynthesis is known. This disease, because of defects in the first step of ganglioside biosynthesis (GM3 synthase), results in a severe epileptic disorder found at high frequency amongst the Old Order Amish. Here we investigated an unusual neurodegenerative phenotype, most commonly classified as a complex form of hereditary spastic paraplegia, present in families from Kuwait, Italy and the Old Order Amish. Our genetic studies identified mutations in B4GALNT1 (GM2 synthase), encoding the enzyme that catalyzes the second step in complex ganglioside biosynthesis, as the cause of this neurodegenerative phenotype. Biochemical profiling of glycosphingolipid biosynthesis confirmed a lack of GM2 in affected subjects in association with a predictable increase in levels of its precursor, GM3, a finding that will greatly facilitate diagnosis of this condition. With the description of two neurological human diseases involving defects in two sequentially acting enzymes in ganglioside biosynthesis, there is the real possibility that a previously unidentified family of ganglioside deficiency diseases exist. The study of patients and animal models of these disorders will pave the way for a greater understanding of the role gangliosides play in neuronal structure and function and provide insights into the development of effective treatment therapies.

Somatic alpha-synuclein mutations in Parkinson's disease: hypothesis and preliminary data

Alpha-synuclein (SNCA) is crucial in the pathogenesis of Parkinson's disease (PD), yet mutations in the SNCA gene are rare. Evidence for somatic genetic variation in normal humans, also involving the brain, is increasing, but its role in disease is unknown. Somatic SNCA mutations, arising in early development and leading to mosaicism, could contribute to PD pathogenesis and yet be absent or undetectable in DNA derived from peripheral lymphocytes. Such mutations could underlie the widespread pathology in PD, with the precise clinical outcome dependent on their type and the timing and location of their occurrence. We recently reported a novel SNCA mutation (c.150T>G, p.H50Q) in PD brain-derived DNA. To determine if there was mosaicism for this, a PCR and cloning strategy was used to take advantage of a nearby heterozygous intronic polymorphism. No evidence of mosaicism was found. High-resolution melting curve analysis of SNCA coding exons, which was shown to be sensitive enough to detect low proportions of 2 known mutations, did not reveal any further mutations in DNA from 28 PD brain-derived samples. We outline the grounds that make the somatic SNCA mutation hypothesis consistent with genetic, embryological, and pathological data. Further studies of brain-derived DNA are warranted and should include DNA from multiple regions and methods for detecting other types of genomic variation. © 2013 Movement Disorder Society

α-Synucleinopathy associated with G51D SNCA mutation: a link between Parkinson's disease and multiple system atrophy?

We report a British family with young-onset Parkinson's disease (PD) and a G51D SNCA mutation that segregates with the disease. Family history was consistent with autosomal dominant inheritance as both the father and sister of the proband developed levodopa-responsive parkinsonism with onset in their late thirties. Clinical features show similarity to those seen in families with SNCA triplication and to cases of A53T SNCA mutation. Post-mortem brain examination of the proband revealed atrophy affecting frontal and temporal lobes in addition to the caudate, putamen, globus pallidus and amygdala. There was severe loss of pigmentation in the substantia nigra and pallor of the locus coeruleus. Neuronal loss was most marked in frontal and temporal cortices, hippocampal CA2/3 subregions, substantia nigra, locus coeruleus and dorsal motor nucleus of the vagus. The cellular pathology included widespread and frequent neuronal α-synuclein immunoreactive inclusions of variable morphology and oligodendroglial inclusions similar to the glial cytoplasmic inclusions of multiple system atrophy (MSA). Both inclusion types were ubiquitin and p62 positive and were labelled with phosphorylation-dependent anti-α-synuclein antibodies In addition, TDP-43 immunoreactive inclusions were observed in limbic regions and in the striatum. Together the data show clinical and neuropathological similarities to both the A53T SNCA mutation and multiplication cases. The cellular neuropathological features of this case share some characteristics of both PD and MSA with additional unique striatal and neocortical pathology. Greater understanding of the disease mechanism underlying the G51D mutation could aid in understanding of α-synuclein biology and its impact on disease phenotype.

A novel α-synuclein missense mutation in Parkinson disease

Alpha-synuclein (SNCA) is central to the pathogenesis of Parkinson disease (PD), with 3 missense mutations reported to date. We report a novel mutation (p.H50Q) in a pathologically proven case.

Hyposmia and cognitive impairment in Gaucher disease patients and carriers

The objective of this study was to assess a cohort of Gaucher disease patients and their heterozygous carrier relatives for potential clinical signs of early neurodegeneration. Gaucher disease patients (n = 30), heterozygous glucocerebrosidase mutation carriers (n = 30), and mutation-negative controls matched by age, sex, and ethnicity (n = 30) were recruited. Assessment was done for olfactory function (University of Pennsylvania Smell Identification Test), cognitive function (Mini-Mental State Examination, Montreal Cognitive Assessment), rapid eye movement sleep disorder, autonomic symptoms, and parkinsonian motor signs (Unified Parkinson’s Disease Rating Scale part III, Purdue pegboard). Olfactory function scores were significantly lower in Gaucher disease patients (P = .010) and heterozygous carriers (P < .001) than in controls. Cognitive assessment scores were significantly lower in Gaucher disease patients (P = .002) and carriers (P = .002) than in controls. Unified Parkinson’s Disease Rating Scale motor subscale scores were significantly higher in Gaucher disease patients (P < .001) and heterozygotes (P = .0010) than in controls. There was no difference in scores for symptoms of rapid eye movement sleep disorder or autonomic dysfunction. Impairment of olfaction, cognition, and parkinsonian motor signs occurs more frequently in Gaucher disease patients and carriers than in controls, which may indicate the early stages of neurodegeneration.

Detection of novel mutations and review of published data suggests that hereditary spastic paraplegia caused by spastin (SPAST) mutations is found more often in males

BACKGROUND

Hereditary spastic paraplegia (HSP) is characterised in its pure form by slowly progressive spastic paraparesis. Around 40% of autosomal dominant (AD) cases are caused by mutations in SPAST, encoding spastin.

PATIENTS AND METHODS

The clinical and investigation details of all patients with a SPAST mutation identified through our centre were reviewed. All published reports of SPAST mutations where the sex of patients was given were subsequently analysed in order to determine whether there is evidence of one sex being preferentially affected.

RESULTS

In total 22 probable pathogenic changes were detected, including 11 novel ones. One patient carried two adjacent missense mutations. The pathogenicity of a further novel missense mutation is uncertain. Most patients had a pure phenotype, although mild peripheral neuropathy was sometimes present. The total number of patients with SPAST mutations was 27, as three of the previously known mutations were present in more than one person. The excess of males over females in our population (17:10) prompted us to review all published studies where the sex of the patients was given (n=31). A significant excess of males was identified (ratio 1.29, p=0.0007).

CONCLUSIONS

Our results are consistent with data suggesting that SPAST mutations mostly cause a pure HSP phenotype. The excess of males in our sample and in published reports suggests that penetrance or severity may be sex-dependent, and merits further investigation as it may have important implications for counselling.

Defective mitochondrial mRNA maturation is associated with spastic ataxia

In human mitochondria, polyadenylation of mRNA, undertaken by the nuclear-encoded mitochondrial poly(A) RNA polymerase, is essential for maintaining mitochondrial gene expression. Our molecular investigation of an autosomal-recessive spastic ataxia with optic atrophy, present among the Old Order Amish, identified a mutation of MTPAP associated with the disease phenotype. When subjected to poly(A) tail-length assays, mitochondrial mRNAs from affected individuals were shown to have severely truncated poly(A) tails. Although defective mitochondrial DNA maintenance underlies a well-described group of clinical disorders, our findings reveal a defect of mitochondrial mRNA maturation associated with human disease and imply that this disease mechanism should be considered in other complex neurodegenerative disorders.

Mutation of FA2H underlies a complicated form of hereditary spastic paraplegia (SPG35)

Hereditary spastic paraplegia (HSP) describes a heterogeneous group of inherited neurodegenerative disorders in which the cardinal pathological feature is upper motor neurone degeneration leading to progressive spasticity and weakness of the lower limbs. Using samples from a large Omani family we recently mapped a gene for a novel autosomal recessive form of HSP (SPG35) in which the spastic paraplegia was associated with intellectual disability and seizures. Magnetic resonance imaging of the brain of SPG35 patients showed white matter abnormalities suggestive of a leukodystrophy. Here we report homozygous mutations in the fatty acid 2-hydroxylase gene (FA2H) in the original family used to define the SPG35 locus (p.Arg235Cys) as well as in a previously unreported Pakistani family with a similar phenotype (p.Arg53_Ile58del). Measurement of enzyme activity in vitro revealed significantly reduced enzymatic function of FA2H associated with these mutations. These results demonstrate that mutations in FA2H are associated with SPG35, and that abnormal hydroxylation of myelin galactocerebroside lipid components can lead to a severe progressive phenotype, with a clinical presentation of complicated HSP and radiological features of leukodystrophy. (c) 2010 Wiley-Liss, Inc.

Early postexercise thallium-201 reinjection after sublingual nitroglycerin augmentation: effects on detection of myocardial ischemia and/or viability

BACKGROUND

Thallium-201 (201Tl) reinjection after conventional redistribution imaging is a standard procedure, resulting in enhanced 201Tl redistribution which is compatible with viable myocardium. Although this method significantly improves identification of viable myocardium, it increases the investigation time by approximately 1 h. Thus, this technique is suboptimal from the standpoint of patient convenience, since its routine performance may be impractical in a high-volume nuclear medicine laboratory.

HYPOTHESIS

This study was undertaken to evaluate the efficacy of an early 201Tl reinjection and imaging protocol in combination with sublingual nitroglycerin, to detect myocardial ischemia and/or viability, and to reduce the need for conventional (4 h) redistribution imaging.

MATERIALS AND METHODS

In this study, 62 consecutive coronary patients, referred for the detection of possible myocardial ischemia and/or viability, were involved (mean age 55 years, range 41-70). Of those, 50 had previous angina attacks, with 42 having a history of previous myocardial infarction; 10 patients had coronary artery bypass grafting; and the remaining 2 had atypical chest pain. Immediately after the completion of the initial postexer-cise imaging, 0.3 mg sublingual nitroglycerin followed by the reinjection of 1 m Ci of 201Tl were administered, and two further sets of images were acquired 1 h and 4 h later.

RESULTS

In each set of images, a total of 496 segments were analyzed. On postexercise imaging, 305 (61%) segments demonstrated defects of which 198 (65%) showed enhanced thallium uptake, 97 (32%) did not change, and 10 (3%) showed reverse redistribution on 1 h reinjection imaging (IRI). Of the 97 persistent defects, only 17 (6%) showed fill-in of 201Tl on 4 h redistribution imaging (CRI), while 12 (4%) segments showed reverse redistribution. On the other hand, after analyzing the 62 patients of the 1 h IRI, 17 (27%) remained unchanged while in only 1 patient (6%) of 17 the diagnosis changed from myocardial necrosis to ischemia after analysis of the 4 h CRI.

CONCLUSION

These results indicate that early postexercise reinjection of 201Tl in combination with sublingual nitroglycerin followed by 1 h image acquisition may prove useful for a comprehensive and convenient assessment of myocardial ischemia and/or viability.