ANXA1 with Anti-Inflammatory Properties Might Contribute to Parkinsonism

We here describe the identification of a novel variant in the anti-inflammatory Annexin A1 protein likely to be the cause of disease in two siblings with autosomal recessive parkinsonism. The disease-segregating variant was ascertained through a combination of homozygosity mapping and whole genome sequencing and was shown to impair phagocytosis in zebrafish mutant embryos. The highly conserved variant, absent in healthy individuals and public SNP databases, affected a functional domain of the protein with neuroprotective properties. This study supports the hypothesis that damaged microglia might lead to impairments in the clearance of accumulated and aggregated proteins resulting in parkinsonism. ANN NEUROL 2021;90:319-323.

Molecular characterization of PRKN structural variations identified through whole-genome sequencing

Background

Early‐onset Parkinson's disease (PD) is the most common inherited form of parkinsonism, with the PRKN gene being the most frequently identified mutated. Exon rearrangements, identified in about 43.2% of the reported PD patients and with higher frequency in specific ethnicities, are the most prevalent PRKN mutations reported to date in PD patients.

Methods

In this study, three consanguineous families with early‐onset PD were subjected to whole‐genome sequencing (WGS) analyses that were followed by Sanger sequencing and droplet digital PCR to validate and confirm the disease segregation of the identified genomic variations and to determine their parental origin.

Results

Five different PRKN structural variations (SVs) were identified. Because the genomic sequences surrounding the break points of the identified SVs might hold important information about their genesis, these were also characterized for the presence of homology and repeated sequences.

Conclusion

We concluded that all identified PRKN SVs might originate through retrotransposition events.

A Novel p.Glu298Lys Mutation in the ACMSD Gene in Sporadic Parkinson's Disease

BACKGROUND

Common genetic variability in the ACMSD gene has been associated with increased risk for Parkinson's disease (PD) but ACMSD mutations in clinical cases of PD have so far not been reported.

OBJECTIVE

To describe a case of sporadic PD carrying a novel ACMSD mutation.

METHODS

As part of a genetic study to identify potential pathogenic gene defects related to PD in the Mediterranean island Menorca, an initial group of 62 PD patients underwent mutational screening using a panel-based sequencing approach.

RESULTS

We report a 74-years-old man with sporadic PD who developed tremor in his right hand and slowness. On examination, moderate rigidity, asymmetric bradykinesia, and bilateral action tremor were present. He was started on levodopa with significant improvement. Two years later, he developed wearing off phenomena. The genetic study in the patient identified a novel ACMSD mutation resulting in p.Glu298Lys amino-acid change which was not present in neurologically normal population.

CONCLUSIONS

Our data suggest that not only common genetic variability but also rare variants in ACMSD alone or in combination with other risk factors might increase the risk of PD.

Whole-exome sequencing associates novel CSMD1 gene mutations with familial Parkinson disease

OBJECTIVE

Despite the enormous advancements made in deciphering the genetic architecture of Parkinson disease (PD), the majority of PD is idiopathic, with single gene mutations explaining only a small proportion of the cases.

METHODS

In this study, we clinically evaluated 2 unrelated Spanish families diagnosed with PD, in which known PD genes were previously excluded, and performed whole-exome sequencing analyses in affected individuals for disease gene identification.

RESULTS

Patients were diagnosed with typical PD without relevant distinctive symptoms. Two different novel mutations were identified in the CSMD1 gene. The CSMD1 gene, which encodes a complement control protein that is known to participate in the complement activation and inflammation in the developing CNS, was previously shown to be associated with the risk of PD in a genome-wide association study.

CONCLUSIONS

We conclude that the CSMD1 mutations identified in this study might be responsible for the PD phenotype observed in our examined patients. This, along with previous reported studies, may suggest the complement pathway as an important therapeutic target for PD and other neurodegenerative diseases.

Support for "Disease-Only" Genotypes and Excess of Homozygosity at the CYTH4 Primate-Specific GTTT-Repeat in Schizophrenia

OBJECTIVE

The role of short tandem repeats (STRs) in the control of gene expression among species is being increasingly understood following the identification of several instances in which certain STRs occur identically, or expand differentially, in primates versus nonprimates. These STRs may regulate genes that participate in characteristics that are associated with the divergence of primates from sibling orders (e.g., brain higher order functions). The CYTH4 gene contains the longest tetranucleotide STR in its core promoter, at 7-repeats, and links to the evolution of human and nonhuman primates. Allele and genotype distribution of this STR were studied in patients affected by schizophrenia (SCZ) and controls.

METHODS

High-resolution data were obtained on the allele and genotype distribution of the CYTH4 STR and a novel C > T single-nucleotide polymorphism (SNP) at its immediate upstream sequence in 255 patients with SCZ and 249 controls. Each sample was sequenced twice using the fluorescent dye termination method.

RESULTS

Novel alleles were detected at the long extreme of the GTTT-repeat, at 10- and 11-repeats, in the SCZ cases and controls. Excess of homozygosity was observed for the entire range of alleles across the GTTT-repeat and the C > T SNP in the SCZ patients in comparison with the controls (Yates corrected p < 0.011). Three genotypes consisting of the 11-repeat allele (i.e., 11/11, 10/11, and 7/11) were detected only in the SCZ patients (i.e., disease-only genotypes), and contributed to 2.3% of the SCZ genotypes (Mid p exact <0.007). The frequency of the 11-repeat allele was estimated at 0.02 and 0.006 in the SCZ patients and controls, respectively (Mid p exact <0.006).

CONCLUSION

This indicates that STR genotypes that are absent in the control group may be risk factors for SCZ. Future studies are warranted to test the significance of our findings.

A novel TRPA1 variant is associated with carbamazepine-responsive cramp-fasciculation syndrome

Cramp-fasciculation syndrome (CFS) is a rare muscle hyperexcitability syndrome that presents with muscle cramps, fasciculations, and stiffness, as well as pain, fatigue, anxiety, hyperreflexia, and paresthesias. Although familial cases have been reported, a genetic etiology has not yet been identified. We performed whole-exome sequencing followed by validation and cosegregation analyses on a father-son pair with CFS. Both subjects manifested other hypersensitivity-hyperexcitability symptoms, including asthma, gastroesophageal reflux, migraine, restless legs syndrome, tremor, cold hyperalgesia, and cardiac conduction defects. Most symptoms improved with carbamazepine, consistent with an underlying cation channelopathy. We identified a variant in the transient receptor potential ankyrin A1 channel (TRPA1) gene that selectively cosegregated with CFS and the other hypersensitivity-hyperexcitability symptoms. This variant (c.2755C>T) resulted in a premature stop codon at amino acid 919 (p.Arg919*) in the outer pore of the channel. TRPA1 is a widely distributed, promiscuous plasmalemmal cation channel that is strongly implicated in the pathophysiology of the specific hypersensitivity-hyperexcitability symptoms observed in these subjects. Thus, we have identified a novel TRPA1 variant that is associated with CFS as part of a generalized hypersensitivity-hyperexcitability disorder. These findings clarify the diverse functional roles of TRPA1, and underscore the importance of this channel as a potential therapeutic target.

Whole genome sequencing identifies a novel homozygous exon deletion in the NT5C2 gene in a family with intellectual disability and spastic paraplegia

Hereditary spastic paraplegias are a rare group of clinically and genetically heterogeneous neurodegenerative diseases, with upper motor neuron degeneration and progressive lower limb spasticity as their main phenotypic features. Despite that 76 distinct loci have been reported and some casual genes identified, most of the underlying causes still remain unidentified. Moreover, a wide range of clinical manifestations is present in most hereditary spastic paraplegias subtypes, adding further complexity to their differential clinical diagnoses. Here, we describe the first exon rearrangement reported in the SPG45/SPG65 (NT5C2) loci in a family featuring a complex hereditary spastic paraplegias phenotype. This study expands both the phenotypic and mutational spectra of the NT5C2-associated disease.

PTRHD1 (C2orf79) mutations lead to autosomal-recessive intellectual disability and parkinsonism

INTRODUCTION

Atypical parkinsonism is a neurodegenerative disease that includes diverse neurological and psychiatric manifestations.

OBJECTIVES

We aimed to identify the disease-cauisng mutations in a consanguineous family featuring intellectual disability and parkinsonism.

METHODS

Full phenotypic characterization, followed by genome-wide single-nucleotide polymorphism genotyping and whole-genome sequencing, was carried out in all available family members.

RESULTS

The chromosome, 2p23.3, was identified as the disease-associated locus, and a homozygous PTRHD1 mutation (c.157C>T) was then established as the disease-causing mutation. The pathogenicity of this PTRHD1 mutation was supported by its segregation with the disease status, its location in a functional domain of the encoding protein, as well as its absence in public databases and ethnicity-matched control chromosomes.

CONCLUSION

Given the role of 2p23 locus in patients with intellectual disability and the previously reported PTRHD1 mutation (c.155G>A) in patients with parkinsonism and cognitive dysfunction, we concluded that the PTRHD1 mutation identified in this study is likely to be responsible for the phenotypic features of the family under consideration. © 2016 International Parkinson and Movement Disorder Society.

Identification of a Large DNAJB2 Deletion in a Family with Spinal Muscular Atrophy and Parkinsonism

In this study, we described the identification of a large DNAJB2 (HSJ1) deletion in a family with recessive spinal muscular atrophy and Parkinsonism. After performing homozygosity mapping and whole genome sequencing, we identified a 3.8 kb deletion, spanning the entire DnaJ domain of the HSJ1 protein, as the disease-segregating mutation. By performing functional assays, we showed that HSJ1b-related DnaJ domain deletion leads to loss of HSJ1b mRNA and protein levels, increased HSJ1a mRNA and protein expressions, increased cell death, protein aggregation, and enhanced autophagy. Given the role of HSJ1 proteins in the degradation of misfolded proteins, we speculated that enhanced autophagy might be promoted by the elevated HSJ1a expression seen in HSJ1b-deficient cells. We also observed a significant reduction in both tau and brain-derived neurotrophic factor levels, which may explain the dopaminergic deficits seen in one of the affected siblings. We concluded that HSJ1b deficiency leads to a complex neurological phenotype, possibly due to the accumulation of misfolded proteins, caused by the lack of the DnaJ domain activity. We thus expand the phenotypic and genotypic spectrums associated with DNAJB2 disease and suggest relevant disease-associated mechanisms.

SCN4A pore mutation pathogenetically contributes to autosomal dominant essential tremor and may increase susceptibility to epilepsy

Essential tremor (ET) is the most prevalent movement disorder, affecting millions of people in the USA. Although a positive family history is one of the most important risk factors for ET, the genetic causes of ET remain unknown. In an attempt to identify genetic causes for ET, we performed whole-exome sequencing analyses in a large Spanish family with ET, in which two patients also developed epilepsy. To further assess pathogenicity, site-directed mutagenesis, mouse and human brain expression analyses, and patch clamp techniques were performed. A disease-segregating mutation (p.Gly1537Ser) in the SCN4A gene was identified. Posterior functional analyses demonstrated that more rapid kinetics at near-threshold potentials altered ion selectivity and facilitated the conductance of both potassium and ammonium ions, which could contribute to tremor and increase susceptibility to epilepsy, respectively. In this report, for the first time, we associated the genetic variability of SCN4A with the development of essential tremor, which adds ET to the growing list of neurological channelopathies.

SORT1 Mutation Resulting in Sortilin Deficiency and p75(NTR) Upregulation in a Family With Essential Tremor

*These authors contributed equally to this work.

Essential tremor (ET) is the most prevalent movement disorder affecting millions of people in the United States. Although a positive family history is one of the most important risk factors for ET, the genetic causes of ET remain unknown. In this study, whole exome sequencing and subsequent approaches were performed in a family with an autosomal dominant form of early-onset ET. Functional analyses including mutagenesis, cell culture, gene expression, enzyme-linked immunosorbent, and apoptosis assays were also performed. A disease-segregating mutation (p.Gly171Ala), absent in normal population, was identified in the SORT1 gene. The p.Gly171Ala mutation was shown not only to impair the expression of its encoding protein sortilin but also the mRNA levels of its binding partner p75 neurotrophin receptor that is known to be implicated in brain injury, neuronal apoptosis, and neurotransmission.

PLA2G6-associated Dystonia-Parkinsonism: Case Report and Literature Review

Background

Phospholipase-associated neurodegeneration (PLAN) caused by PLA2G6 mutations is a recessively inherited disorder with three known phenotypes: the typical infantile onset neuroaxonal dystrophy (INAD); an atypical later onset form (atypical NAD); and the more recently recognized young-onset dystonia–parkinsonism (PLAN-DP).

Case Report

We report the clinical, radiological, and genetic findings of a young Pakistani male with PLAN-DP. We review 11 previously published case reports cited in PubMed, and summarize the demographic, clinical, genetic, and radiological data of the 23 patients described in those articles.

Discussion

PLAN-DP presents with diverse motor, autonomic, and neuropsychiatric features and should be considered in the differential diagnosis of patients with young-onset neurodegenerative disorders.

LRRK2: cause, risk, and mechanism

In 2004 it was first shown that mutations in LRRK2 can cause Parkinson's disease. This initial discovery was quickly followed by the observation that a single particular mutation is a relatively common cause of Parkinson's disease across varied populations. Further genetic investigation has revealed a variety of genetic ties to Parkinson's disease across this gene. These include common alleles with quite broad effects on risk, likely through both alterations at the protein sequence level, and in the context of expression. A great deal of functional characterization of LRRK2 and disease-causing mutations in this protein has occurred over the last 9 years, and considerable progress has been made. Particular attention has been paid to the kinase activity of LRRK2 as a therapeutic target, and while it is no means certain that this is viable target it is likely that this hypothesis will be tested in clinical trials sooner rather than later. We believe that the future goals for LRRK2 research are, while challenging, relatively clear and that the next 10 years of research promises to be perhaps more exciting than the last.

Mutations in γ adducin are associated with inherited cerebral palsy

OBJECTIVE

Cerebral palsy is estimated to affect nearly 1 in 500 children, and although prenatal and perinatal contributors have been well characterized, at least 20% of cases are believed to be inherited. Previous studies have identified mutations in the actin-capping protein KANK1 and the adaptor protein-4 complex in forms of inherited cerebral palsy, suggesting a role for components of the dynamic cytoskeleton in the genesis of the disease.

METHODS

We studied a multiplex consanguineous Jordanian family by homozygosity mapping and exome sequencing, then used patient-derived fibroblasts to examine functional consequences of the mutation we identified in vitro. We subsequently studied the effects of adducin loss of function in Drosophila.

RESULTS

We identified a homozygous c.1100G>A (p.G367D) mutation in ADD3, encoding gamma adducin in all affected members of the index family. Follow-up experiments in patient fibroblasts found that the p.G367D mutation, which occurs within the putative oligomerization critical region, impairs the ability of gamma adducin to associate with the alpha subunit. This mutation impairs the normal actin-capping function of adducin, leading to both abnormal proliferation and migration in cultured patient fibroblasts. Loss of function studies of the Drosophila adducin ortholog hts confirmed a critical role for adducin in locomotion.

INTERPRETATION

Although likely a rare cause of cerebral palsy, our findings indicate a critical role for adducins in regulating the activity of the actin cytoskeleton, suggesting that impaired adducin function may lead to neuromotor impairment and further implicating abnormalities of the dynamic cytoskeleton as a pathogenic mechanism contributing to cerebral palsy.

The ACMSD gene, involved in tryptophan metabolism, is mutated in a family with cortical myoclonus, epilepsy, and parkinsonism

Familial cortical myoclonic tremor and epilepsy is a phenotypically and genetically heterogeneous autosomal dominant disorder characterized by the presence of cortical myoclonic tremor and epilepsy that is often accompanied by additional neurological features. Despite the numerous familial studies performed and the number of loci identified, there is no gene associated with this syndrome. It is expected that through the application of novel genomic technologies, such as whole exome sequencing and whole genome sequencing, a substantial number of novel genes will come to light in the coming years. In this study, we describe the identification of two disease-segregating mutations in a large family featuring cortical myoclonic tremor with epilepsy and parkinsonism. Due to the previous association of ACMSD deficiency with the development of epileptic seizures, we concluded that the identified nonsense mutation in the ACMSD gene, which encodes for a critical enzyme of the kynurenine pathway of the tryptophan metabolism, is the disease-segregating mutation most likely to be responsible for the phenotype described in our family. This finding not only reveals the identification of the first gene associated with familial cortical myoclonic tremor and epilepsy but also discloses the kynurenine pathway as a potential therapeutic target for the treatment of this devastating syndrome.

KEY MESSAGE

ACMSD is mutated in a family with cortical myoclonus, epilepsy, and parkinsonism. ACMSD mutation contributes to the development of FCMTE QA accumulation is likely to play an important role in the pathogenesis of FCMTE. The kynurenine pathway as a potential drug target for the treatment of epilepsy.

The Sac1 domain of SYNJ1 identified mutated in a family with early-onset progressive Parkinsonism with generalized seizures

This study aimed to elucidate the genetic causes underlying early-onset Parkinsonism (EOP) in a consanguineous Iranian family. To attain this, homozygosity mapping and whole-exome sequencing were performed. As a result, a homozygous mutation (c.773G>A; p.Arg258Gln) lying within the NH2 -terminal Sac1-like inositol phosphatase domain of polyphosphoinositide phosphatase synaptojanin 1 (SYNJ1), which has been implicated in the regulation of endocytic traffic at synapses, was identified as the disease-segregating mutation. This mutation impaired the phosphatase activity of SYNJ1 against its Sac1 domain substrates in vitro. We concluded that the SYNJ1 mutation identified here is responsible for the EOP phenotype seen in our patients probably due to deficiencies in its phosphatase activity and consequent impairment of its synaptic functions. Our finding not only opens new avenues of investigation in the synaptic dysfunction mechanisms associated with Parkinsonism, but also suggests phosphoinositide metabolism as a novel therapeutic target for Parkinsonism.

Kohlschütter-Tönz syndrome: mutations in ROGDI and evidence of genetic heterogeneity

Kohlschütter-Tönz syndrome (KTS) is a rare autosomal recessive disorder characterized by amelogenesis imperfecta, psychomotor delay or regression and seizures starting early in childhood. KTS was established as a distinct clinical entity after the first report by Kohlschütter in 1974, and to date, only a total of 20 pedigrees have been reported. The genetic etiology of KTS remained elusive until recently when mutations in ROGDI were independently identified in three unrelated families and in five likely related Druze families. Herein, we report a clinical and genetic study of 10 KTS families. By using a combination of whole exome sequencing, linkage analysis, and Sanger sequencing, we identify novel homozygous or compound heterozygous ROGDI mutations in five families, all presenting with a typical KTS phenotype. The other families, mostly presenting with additional atypical features, were negative for ROGDI mutations, suggesting genetic heterogeneity of atypical forms of the disease.

R632W mutation in PLA2G6 segregates with dystonia-parkinsonism in a consanguineous Iranian family

BACKGROUND

PLA2G6 mutations are known to be responsible for infantile neuroaxonal dystrophy (INAD) and neurodegeneration with brain iron accumulation (NBIA). In addition, novel mutations in PLA2G6 have recently been associated with dystonia-parkinsonism in two unrelated consanguineous families.

METHODS

Direct sequencing analysis of the PLA2G6 gene.

RESULTS

Here, we report the segregation of R632W with disease in an Iranian consanguineous dystonia-parkinsonism pedigree. The identical mutation was previously observed in a patient affected with NBIA.

CONCLUSION

We conclude that different and even identical PLA2G6 mutations may cause neurodegenerative diseases with heterogeneous clinical manifestations, including INAD, NBIA and dystonia-parkinsonism.

The use of next-generation sequencing in movement disorders

New advances in genomic technology are being introduced at a greater speed and are revolutionizing the field of genetics for both complex and Mendelian diseases. For instance, during the past few years, genome-wide association studies (GWAS) have identified a large number of significant associations between genomic loci and movement disorders such as Parkinson's disease and progressive supranuclear palsy. GWAS are carried out through the use of high-throughput SNP genotyping arrays, which are also used to perform linkage analyses in families previously considered statistically underpowered for genetic analyses. In inherited movement disorders, using this latter technology, it has repeatedly been shown that mutations in a single gene can lead to different phenotypes, while the same clinical entity can be caused by mutations in different genes. This is being highlighted with the use of next-generation sequencing technologies and leads to the search for genes or genetic modifiers that contribute to the phenotypic expression of movement disorders. Establishing an accurate genome-epigenome-phenotype relationship is becoming a major challenge in the post-genomic research that should be facilitated through the implementation of both functional and cellular analyses.

Glucocerebrosidase mutations confer a greater risk of dementia during Parkinson's disease course

Mutations in the glucocerebrosidase gene are associated with Parkinson's disease and Lewy body dementia. However, whether these alterations have any effect on the clinical course of Parkinson's disease is not clear. The glucocerebrosidase coding region was fully sequenced in 225 Parkinson's disease patients, 17 pathologically confirmed Lewy body dementia patients, and 186 controls from Spain. Twenty-two Parkinson's disease patients (9.8%) and 2 Lewy body dementia patients (11.8%) carried mutations in the glucocerebrosidase gene, compared with only 1 control (0.5%); P = .016 and P = .021 for Parkinson's disease and Lewy body dementia, respectively. The N370S and the L444P mutations represented 50% of the alterations. Two novel variants, L144V and S488T, and 7 previously described alterations were also found. Alterations in glucocerebrosidase were associated with a significant risk of dementia during the clinical course of Parkinson's disease (age at onset, years of evolution, and sex-adjusted odds ratio, 5.8; P = .001). Mutation carriers did not show worse motor symptoms, had good response to L-dopa, and tended to present the intermediate parkinsonian phenotype. Our findings suggest that mutations in the glucocerebrosidase gene not only increase the risk of both Parkinson's disease and Lewy body dementia but also strongly influence the course of Parkinson's disease with respect to the appearance of dementia.

Thinning of the corpus callosum and cerebellar atrophy is correlated with phenotypic severity in a family with spastic paraplegia type 11

Background

Mutations in the spatacsin gene are associated with spastic paraplegia type 11 (SPG11), which is the most-common cause of autosomal recessive hereditary spastic paraplegia. Although SPG11 has diverse phenotypes, thinning of the corpus callosum is an important feature.

Case Report

Clinical, genetic, and radiological evaluations were undertaken in a large family from Gujarat in North India with hereditary spastic paraplegia, whose affected members presented with varying degrees of spasticity, ataxia, and cognitive impairment. The clinical severity and the degree of corpus callosum and cerebellar atrophy varied among the four affected individuals in the family. Genetic testing of the affected members revealed recessive mutations in the spatacsin gene, consistent with a diagnosis of SPG11.

Conclusions

We believe that the extent of corpus callosum thinning and cerebellar atrophy is correlated with disease severity in affected patients. The addition of extrapyramidal features in the most-affected members suggests that SPG11 exhibits considerable phenotypic heterogeneity.

Early-onset L-dopa-responsive parkinsonism with pyramidal signs due to ATP13A2, PLA2G6, FBXO7 and spatacsin mutations

Seven autosomal recessive genes associated with juvenile and young-onset Levodopa-responsive parkinsonism have been identified. Mutations in PRKN, DJ-1, and PINK1 are associated with a rather pure parkinsonian phenotype, and have a more benign course with sustained treatment response and absence of dementia. On the other hand, Kufor-Rakeb syndrome has additional signs, which distinguish it clearly from Parkinson's disease including supranuclear vertical gaze palsy, myoclonic jerks, pyramidal signs, and cognitive impairment. Neurodegeneration with brain iron accumulation type I (Hallervorden-Spatz syndrome) due to mutations in PANK2 gene may share similar features with Kufor-Rakeb syndrome. Mutations in three other genes, PLA2G6 (PARK14), FBXO7 (PARK15), and Spatacsin (SPG11) also produce clinical similar phenotypes in that they presented with rapidly progressive parkinsonism, initially responsive to Levodopa treatment but later, developed additional features including cognitive decline and loss of Levodopa responsiveness. Here, using homozygosity mapping and sequence analysis in families with complex parkinsonisms, we identified genetic defects in the ATP13A2 (1 family), PLA2G6 (1 family) FBXO7 (2 families), and SPG11 (1 family). The genetic heterogeneity was surprising given their initially common clinical features. On careful review, we found the FBXO7 cases to have a phenotype more similar to PRKN gene associated parkinsonism. The ATP13A2 and PLA2G6 cases were more seriously disabled with additional swallowing problems, dystonic features, severe in some, and usually pyramidal involvement including pyramidal weakness. These data suggest that these four genes account for many cases of Levodopa responsive parkinsonism with pyramidal signs cases formerly categorized clinically as pallido-pyramidal syndrome.

Defective FA2H leads to a novel form of neurodegeneration with brain iron accumulation (NBIA)

OBJECTIVE

Neurodegeneration with brain iron accumulation (NBIA) represents a distinctive phenotype of neurodegenerative disease for which several causative genes have been identified. The spectrum of neurologic disease associated with mutations in NBIA genes is broad, with phenotypes that range from infantile neurodegeneration and death in childhood to adult-onset parkinsonism-dystonia. Here we report the discovery of a novel gene that leads to a distinct form of NBIA.

METHODS

Using autozygosity mapping and candidate gene sequencing, we identified mutations in the fatty acid hydroxylase gene FA2H, newly implicating abnormalities of ceramide metabolism in the pathogenesis of NBIA.

RESULTS

Neuroimaging demonstrated T2 hypointensity in the globus pallidus, confluent T2 white matter hyperintensities, and profound pontocerebellar atrophy in affected members of two families. Phenotypically, affected family members exhibited spastic quadriparesis, ataxia, and dystonia with onset in childhood and episodic neurological decline. Analogous to what has been reported previously for PLA2G6, the phenotypic spectrum of FA2H mutations is diverse based on our findings and those of prior investigators, because FA2H mutations have been identified in both a form of hereditary spastic paraplegia (SPG35) and a progressive familial leukodystrophy.

INTERPRETATION

These findings link white matter degeneration and NBIA for the first time and implicate new signaling pathways in the genesis of NBIA.

Genetic variability at the PARK16 locus

Parkinson's disease (PD) is a complex neurodegenerative disease which is clinically heterogeneous and pathologically consists of loss of dopaminergic neurons in the substantia nigra and intracytoplasmic neuronal inclusions containing alpha-synuclein aggregations known as Lewy bodies. Although the majority of PD is idiopathic, pathogenic mutations in several mendelian genes have been successfully identified through linkage analyses. To identify susceptibility loci for idiopathic PD, several genome-wide association studies (GWAS) within different populations have recently been conducted in both idiopathic and familial forms of PD. These analyses have confirmed SNCA and MAPT as loci harboring PD susceptibility. In addition, the GWAS identified several other genetic loci suggestively associated with the risk of PD; among these, only one was replicated by two different studies of European and Asian ancestries. Hence, we investigated this novel locus known as PARK16 for coding mutations in a large series of idiopathic pathologically proven PD cases, and also conducted an association study in a case-control cohort from the United Kingdom. An association between a novel RAB7L1 mutation, c.379-12insT, and disease (P-value=0.0325) was identified. Two novel coding variants present only in the PD cohort were also identified within the RAB7L1 (p.K157R) and SLC41A1 (p.A350V) genes. No copy number variation analyses have yet been performed within this recently identified locus. We concluded that, although both coding variants and risk alleles within the PARK16 locus seem to be rare, further molecular analyses within the PARK16 locus and within different populations are required in order to examine its biochemical role in the disease process.

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.

Widespread Lewy body and tau accumulation in childhood and adult onset dystonia-parkinsonism cases with PLA2G6 mutations

The 2 major types of neurodegeneration with brain iron accumulation (NBIA) are the pantothenate kinase type 2 (PANK2)-associated neurodegeneration (PKAN) and NBIA2 or infantile neuroaxonal dystrophy (INAD) due to mutations in the phospholipase A2, group VI (PLA2G6) gene. We have recently demonstrated clinical heterogeneity in patients with mutations in the PLA2G6 gene by identifying a poorly defined subgroup of patients who present late with dystonia and parkinsonism. We report the clinical and genetic features of 7 cases with PLA2G6 mutations. Brain was available in 5 cases with an age of death ranging from 8 to 36 years and showed widespread alpha-synuclein-positive Lewy pathology, which was particularly severe in the neocortex, indicating that the Lewy pathology spread corresponded to Braak stage 6 and was that of the “diffuse neocortical type”. In 3 cases there was hyperphosphorylated tau accumulation in both cellular processes as threads and neuronal perikarya as pretangles and neurofibrillary tangles. Later onset cases tended to have less tau involvement but still severe alpha-synuclein pathology. The clinical and neuropathological features clearly represent a link between PLA2G6 and parkinsonian disorders.

Homozygosity mapping through whole genome analysis identifies a COL18A1 mutation in an Indian family presenting with an autosomal recessive neurological disorder

The use of genome wide genotyping arrays has the potential to assess entire groups of genetic disorders in one application and has begun to emerge as an aid to diagnosis in clinical practice. Recessive families may suffer from diseases because of homozygosity of recessive alleles; homozygosity tracks can be easily identified by using these high throughput SNPs arrays, allowing the rapid mapping of autozygous segments that may be associated with the disease. According to this, we performed homozygosity mapping using genome wide SNP arrays in a North Indian family with an autosomal recessive disorder of ataxia, epilepsy, cognitive decline and visual problems. In this kindred, a large number of homozygous regions were identified. In silico analysis was also carried out. The COL18A1 gene found in one of the homozygous tracks has genetic defects previously reported with a similar phenotype as our family. Hence, it was the most likely candidate gene and at large the first to be analyzed. A homozygous COL18A1 two base pair deletio segregating with the disease was identified; expanding the spectrum of disease seen in COL18A1 and proving that the genetic lesion underlying recessive disorders can rapidly identify by employing genotyping arrays along with detailed candidate gene analysis.

Loss of function mutations in the gene encoding latent transforming growth factor beta binding protein 2, LTBP2, cause primary congenital glaucoma

Glaucoma is a heterogeneous group of optic neuropathies that manifests by optic nerve head cupping or degeneration of the optic nerve, resulting in a specific pattern of visual field loss. Glaucoma leads to blindness if left untreated, and is considered the second leading cause of blindness worldwide. The subgroup primary congenital glaucoma (PCG) is characterized by an anatomical defect in the trabecular meshwork, and age at onset in the neonatal or infantile period. It is the most severe form of glaucoma. CYP1B1 was the first gene genetically linked to PCG, and CYP1B1 mutations are the cause of disease in 20-100% of patients in different populations. Here, we report that LTBP2 encoding latent transforming growth factor beta binding protein 2 is a PCG causing gene, confirming results recently reported. A disease-associated locus on chromosome 14 was identified by performing whole genome autozygosity mapping in Iranian PCG families using high density single nucleotide polymorphism chips, and two disease-segregating loss of function mutations in LTBP2, p.Ser472fsX3 and p.Tyr1793fsX55, were observed in two families while sequencing candidate genes in the locus. The p.Tyr1793fsX55 mutation affects an amino acid close to the C-terminal of the encoded protein. Subsequently, LTBP2 expression was shown in human eyes, including the trabecular meshwork and ciliary processes that are thought to be relevant to the etiology of PCG.

Parkinson's disease and low frequency alleles found together throughout LRRK2

Mutations within LRRK2, most notably p.G2019S, cause Parkinson's disease (PD) in rare monogenic families, and sporadic occurrences in diverse populations. We investigated variation throughout LRRK2 (84 SNPs; genotype or diplotype found for 49 LD blocks) for 275 cases (European ancestry, onset at age 60 or older) and 275 neurologically healthy control subjects (NINDS Neurogenetics Repository). Three grade-of-membership groups, i.e. genetic risk sets, were identified that exactly matched many subjects (cases: 46, 4, 137; controls: 0, 178, 0), and distinguished 94% of the subjects (i.e. >50% likeness to one set). Set I, affected, carried certain low frequency alleles located in multiple functional domains. Set II was unaffected. Set III, also affected, resembled set II except for slightly elevated frequencies of minor alleles not defining set I. We conclude that certain low frequency alleles distributed throughout LRRK2 are a genetic background to a third of cases, defining a distinct subset.

Whole genome analysis in a consanguineous family with early onset Alzheimer's disease

Early-onset Alzheimer's disease (EOAD) is a clinically and genetically heterogeneous condition in which the typical features appear significantly earlier in life (before 65 years). Mutations in three genes (PSEN1, PSEN2, and APP) have been identified in autosomal dominant forms of EOAD. However, in about 50% of Mendelian cases and in most of the sporadic EOAD patients, no mutations have been found. We present clinical characteristics of an Israeli family comprising two affected siblings with EOAD born to neurologically healthy parents who were first cousins (both parents died after 90 years old). Sequence analysis of PSEN1, PSEN2, APP, TAU, PGRN, and PRNP failed to reveal any mutations in the affected siblings. Because the disease in this family is consistent with an autosomal recessive mode of inheritance we identified all homozygous regions identical by descent (IBD) in both siblings, by high-density SNP genotyping. We provide here the first catalog of autozygosity in EOAD and suggest that the regions identified are excellent candidate loci for a recessive genetic lesion causing this disease.

Parkinson's disease due to the R1441G mutation in Dardarin: a founder effect in the Basques

The recent discovery of mutations in Dardarin (LRRK2) have been related to the appearance of Parkinson's disease in several families. Notably, one single mutation in this gene (R1441G) not only appeared in familial, but also in apparently sporadic Parkinson disease (PD) patients of Basque descent. A clinical population was ascertained, and subjects were classified into Basque and non-Basque descent according to their known ancestry. The R1441G mutation was assayed using an allele-specific polymerase chain reaction, and several single nucleotide polymorphisms surrounding this mutation were analyzed by direct sequencing. In addition to 22 members of the original Basque families where R1441G was identified, we observed 17 carriers of the mutation who were apparently related through a common ancestor. From a clinical perspective, the disease observed in mutation carriers is indistinguishable from that in noncarriers. The R1441G mutation causes a form of Parkinson's disease that is equivalent to that observed in idiopathic Parkinson's disease. This mutation appears in 16.4% and 4.0% of familial and sporadic PD in this Basque population, respectively.

Apolipoprotein E epsilon4 allele in familial and sporadic Parkinson's disease

Parkinson's disease (PD) is the second most common age-related neurodegenerative disease after Alzheimer's disease (AD). Common risk factors for both diseases have been explored to study potential etiologic interactions between these two neurodegenerative disorders. The APOE epsilon4 allele, previously associated with AD, has also been associated with risk of PD and with the presence of some clinical features in PD patients. However, the role of APOE epsilon4 allele in risk of PD remains unclear. We studied the distribution of APOE alleles in 276 unrelated familial and sporadic PD patients and in 212 controls. Patients and controls were classified by ethnicity. No genetic heterogeneity between Basques and people from other regions of Spain was found. No significant differences in APOE allele distribution between PD patients and controls were found; however, lower epsilon4 allele frequency was observed when the sporadic PD group was analyzed separately. By contrast, an increase in epsilon4 allele frequency was found in familial PD patients with cognitive decline. We conclude that the APOE epsilon4 allele may be associated with the risk of developing PD in isolated cases and that it is linked to the presence of cognitive decline in familial PD in our sample.