Genetic characterization of a cohort with familial parkinsonism and cognitive-behavioral syndrome: A Next Generation Sequencing study.

OBJECTIVE: To perform the genetic characterization of a cohort with familial parkinsonism and cognitive-behavioral syndrome. METHODS: A Next Generation Sequencing - based targeted sequencing of 32 genes associated to various neurodegenerative phenotypes, plus a screening for SNCA Copy Number Variations and C9orf72 repeat expansion, was applied in a cohort of 85 Italian patients presenting with parkinsonism and cognitive and/or behavioral syndrome and a positive familial history for any neurodegenerative disorder (i.e., dementia, movement disorders, amyotrophic lateral sclerosis). RESULTS: Through this combined genetic approach, we detected potentially relevant genetic variants in 25.8% of patients with familial parkinsonism and cognitive and/or behavioral syndrome. Peculiar phenotypes are described (Cortico-basal syndrome with APP, Posterior Cortical Atrophy with GBA, Progressive Supranuclear Palsy-like with GRN, Multiple System Atrophy with TARDBP). The majority of patients presented a rigid-bradykinetic parkinsonian syndrome, while rest tremor was less common. Myoclonic jerks, pyramidal signs, dystonic postures and vertical gaze disturbances were more frequently associated with the presence of a pathogenic variant in one of the tested genes. CONCLUSIONS: Given the syndromic approach adopted in our study, we were able to provide a detailed clinical description of patients beyond the boundaries of specific clinical diagnoses and describe peculiar phenotypes. This observation further supports the knowledge that genetic disorders present phenotypic overlaps across different neurodegenerative syndromes, highlighting the limitations of current clinical diagnostic criteria defining sharp boundaries between distinct conditions.

Opposing patterns of abnormal D1 and D2 receptor dependent cortico-striatal plasticity explain increased risk taking in patients with DYT1 dystonia.

Patients with DYT1 dystonia caused by the mutated TOR1A gene exhibit risk neutral behaviour compared to controls who are risk averse in the same reinforcement learning task. It is unclear whether this behaviour can be linked to changes in cortico-striatal plasticity demonstrated in animal models which share the same TOR1A mutation. We hypothesised that we could reproduce the experimental risk taking behaviour using a model of the basal ganglia under conditions where cortico-striatal plasticity was abnormal. As dopamine exerts opposing effects on cortico-striatal plasticity via different receptors expressed on medium spiny neurons (MSN) of the direct (D1R dominant, dMSNs) and indirect (D2R dominant, iMSNs) pathways, we tested whether abnormalities in cortico-striatal plasticity in one or both of these pathways could explain the patient's behaviour. Our model could generate simulated behaviour indistinguishable from patients when cortico-striatal plasticity was abnormal in both dMSNs and iMSNs in opposite directions. The risk neutral behaviour of the patients was replicated when increased cortico-striatal long term potentiation in dMSN's was in combination with increased long term depression in iMSN's. This result is consistent with previous observations in rodent models of increased cortico-striatal plasticity at in dMSNs, but contrasts with the pattern reported in vitro of dopamine D2 receptor dependant increases in cortico-striatal LTP and loss of LTD at iMSNs. These results suggest that additional factors in patients who manifest motor symptoms may lead to divergent effects on D2 receptor dependant cortico-striatal plasticity that are not apparent in rodent models of this disease.

A Missense Mutation A384P Associated with Human Hyperekplexia Reveals a Desensitization Site of Glycine Receptors.

Hyperekplexia, an inherited neuronal disorder characterized by exaggerated startle responses with unexpected sensory stimuli, is caused by dysfunction of glycinergic inhibitory transmission. From analysis of newly identified human hyperekplexia mutations in the glycine receptor (GlyR) α1 subunit, we found that an alanine-to-proline missense mutation (A384P) resulted in substantially higher desensitization level and lower agonist sensitivity of homomeric α1 GlyRs when expressed in HEK cells. The incorporation of the ß subunit fully reversed the reduction in agonist sensitivity and partially reversed the desensitization of α1A384P The heteromeric α1A384Pß GlyRs showed enhanced desensitization but unchanged agonist-induced maximum responses, surface expression, main channel conductance, and voltage dependence compared with that of the wild-type α1ß (α1WTß) GlyRs. Coexpression of the R392H and A384P mutant α1 subunits, which mimic the expression of the compound heterozygous mutation in a hyperekplexia patient, resulted in channel properties similar to those with α1A384P subunit expression alone. In comparison, another human hyperekplexia mutation α1P250T, which was previously reported to enhance desensitization, caused a strong reduction in maximum currents in addition to the altered desensitization. These results were further confirmed by overexpression of α1P250T or α1A384P subunits in cultured neurons isolated from SD rats of either sex. Moreover, the IPSC-like responses of cells expressing α1A384Pß induced by repeated glycine pulses showed a stronger frequency-dependent reduction than those expressing α1WTß. Together, our findings demonstrate that A384 is associated with the desensitization site of the α1 subunit and its proline mutation produced enhanced desensitization of GlyRs, which contributes to the pathogenesis of human hyperekplexia.SIGNIFICANCE STATEMENT Human startle disease is caused by impaired synaptic inhibition in the brainstem and spinal cord, which is due to either direct loss of GlyR channel function or reduced number of synaptic GlyRs. Considering that fast decay kinetics of GlyR-mediated inhibitory synaptic responses, the question was raised whether altered desensitization of GlyRs will cause dysfunction of glycine transmission and disease phenotypes. Here, we found that the α1 subunit mutation A384P, identified from startle disease patients, results in enhanced desensitization and leads to rapidly decreasing responses in the mutant GlyRs when they are activated repeatedly by the synaptic-like simulation. These observations suggest that the enhanced desensitization of postsynaptic GlyRs could be the primary pathogenic mechanism of human startle disease.

The Incidence and Evolution of Parkinsonian Rigidity in Rett Syndrome: A Pilot Study.

BACKGROUND: Patients with Rett syndrome (RTT) may demonstrate parkinsonian features. Here, we report a preliminary cross-sectional and prospective evaluation of the evolution, regional distribution, and eventual incidence of rigid tone in a cohort of MECP2 mutation-positive patients. METHODS: In 51 participants, muscle tone rigidity in extremity regions and neck plus hypomimia were quantified using an RTT rigidity distribution (RTTRD) score with a range of 0 to 15. RTTRD scores were correlated with age, ability to walk and speak, mutation type, and, in a small subgroup (n=9), cerebrospinal fluid (CSF) homovanillic acid (HVA) and 5-hydroxyindole-acetic acid levels. RESULTS: Participant ages ranged from 2 years and 5 months, to 54 years. Rigidity was found in 43/51 (84.3%); it appeared as early as age 3, increased in extent with age, and was present in all participants aged ≥13. Ankle region rigidity appeared first, followed by proximal legs, arms, neck, and face. Ambulatory participants (n=21) had lower RTTRD scores than nonambulatory (n=30; p=0.003). We found a trend to lower scores in participants with retained speech (n=13) versus those with none (n=38; p=0.074), and no difference in scores for those with truncating (n=25) versus missense mutations (n=22; p=0.387). RTTRD scores correlated negatively with CSF HVA levels (R=-0.83; p=0.005), but not with 5-hydroxyindole-acetic acid levels (R=-0.45; p=0.22). CONCLUSIONS: Although assessment of muscle tone is somewhat subjective and the RTTRD has not been validated, this study nevertheless suggests that parkinsonian rigidity in RTT is common and frequently increases in extent with age; its severity correlates directly with impaired ambulation and inversely with CSF HVA levels.

Early-onset Parkinson's Disease Associated with Chromosome 22q11.2 Deletion Syndrome.

We herein report the case of a 43-year-old man with a 4-year history of resting tremor and akinesia. His resting tremor and rigidity were more prominent on the left side. He also presented retropulsion. His symptoms responded to the administration of levodopa. The patient also had a cleft lip and palate, cavum vergae, and hypoparathyroidism. A chromosome analysis disclosed a hemizygous deletion in 22q11.2, and he was diagnosed with early-onset Parkinson's disease associated with 22q11.2 deletion syndrome. However, the patient lacked autonomic nerve dysfunction, and his cardiac uptake of (123)I-metaiodobenzylguanidine was normal, indicating an underlying pathological mechanism that differed to that of sporadic Parkinson's disease.

The relationship between essential tremor and Parkinson's disease.

Essential tremor (ET) and Parkinson's disease (PD) are the two most common tremor disorders encountered in a movement disorders clinic. Although distinct clinical-pathological entities, both disorders may share overlapping features in addition to rest and postural tremor, such as bradykinesia, rigidity, gait and balance impairment and some non-motor signs. A subset of patients may have a combination of long-standing ET with subsequent PD (ET-PD). There are several lines of evidence from clinical, epidemiologic, imaging, genetic and pathologic studies supporting a link between ET and PD, greater than by chance alone. In this review we will discuss the latest data supporting a relationship between ET and PD and the implications for possible pathogenic link and treatment.

Lethal Neonatal Rigidity and Multifocal Seizure Syndrome--A Misnamed Disorder?

OBJECTIVE: Lethal neonatal rigidity and multifocal seizure syndrome is a newly recognized genetic disorder associated with early onset of rigidity, multifocal epilepsy, developmental arrest, and early death. It is an autosomal recessive condition resulting from a mutation in the BRAT1 (BRCA1 [breast cancer-1]-associated ataxia telangiectasia mutated activator 1) gene. There are few cases in the literature, and all patients have died before age 2 years, most within the first 6 months of life. The objective of this report is to expand the phenotypic spectrum of BRAT1 disorders and propose new nomenclature for this condition. RESULTS: We describe a child with compound heterozygosity for mutations in BRAT1. Her neonatal course was unremarkable. Over the first year of life she was noted to have progressive global developmental delay, visual impairment, microcephaly, hypertonia, hyperreflexia, and seizures. No epileptiform discharges were seen on electroencephalogram. Serial magnetic resonance imaging of the brain showed progressive cerebellar and brainstem atrophy. Unlike previously described patients, our patient has gained a number of developmental skills and, at this time, is 3 years and 8 months old. CONCLUSION: Despite the name of this disorder, patients with lethal neonatal rigidity and multifocal seizure syndrome may not present until after the neonatal period and may have a much longer life span than previously reported. We suggest renaming the condition "BRAT1-associated neurodegenerative disorder" to avoid the assumptions associated with the original nomenclature and to encourage clinicians to consider this condition outside the neonatal period.

[Tyrosine hydroxylase deficiency: a case of autosomal recessive dopa-responsive dystonia].

OBJECTIVE: To analyze the clinical characteristics of the patient with tyrosine hydroxylase deficiency, and investigate it's molecular mechanism. METHOD: The clinical characteristics of a patient with tyrosine hydroxylase deficiency were summarized and analyzed, his and his family's peripheral blood specimens were collected after informed consent was signed. All exons and the intron-exon boundaries of guanosine triphosphate hydroxylase I gene, tyrosine hydroxylase gene and sepiapterin reductase gene were examined by DNA-PCR, bi-directional sequencing. RESULT: The patient was a 3-year-old boy, presented with unexplained dystonia for 3 years, without significant impairment of intelligence. Physical examination showed limb muscle strength grade V, rigidity of extremities, hypertonicity, brisk deep tendon reflexes in limbs, without obvious abnormalities in auxiliary examination, such as brain MRI, hepatic biochemical panel, creatine kinase, and ceruloplasmin. He dramatically responded to small doses of levodopa in the follow-up for half a year. A homozygous missense change in exon 5 of TH gene, c.605G > A (p.R202H), which was a known pathogenic mutation, was found in the patient. His parents were heterozygous for the R202H mutation. CONCLUSION: The age of onset in tyrosine hydroxylase deficiency patients is usually within the first year of life. Unexplained dystonia and hypokinesia were the main clinical features of tyrosine hydroxylase deficiency. The dopa-responsive effects for some patients are so obvious that we should strengthen awareness of the disease. TH gene c.605G > A (p.R202H) may be a common type of causative mutations for the mild form at home and abroad.

New hyperekplexia mutations provide insight into glycine receptor assembly, trafficking, and activation mechanisms.

Hyperekplexia is a syndrome of readily provoked startle responses, alongside episodic and generalized hypertonia, that presents within the first month of life. Inhibitory glycine receptors are pentameric ligand-gated ion channels with a definitive and clinically well stratified linkage to hyperekplexia. Most hyperekplexia cases are caused by mutations in the α1 subunit of the human glycine receptor (hGlyR) gene (GLRA1). Here we analyzed 68 new unrelated hyperekplexia probands for GLRA1 mutations and identified 19 mutations, of which 9 were novel. Electrophysiological analysis demonstrated that the dominant mutations p.Q226E, p.V280M, and p.R414H induced spontaneous channel activity, indicating that this is a recurring mechanism in hGlyR pathophysiology. p.Q226E, at the top of TM1, most likely induced tonic activation via an enhanced electrostatic attraction to p.R271 at the top of TM2, suggesting a structural mechanism for channel activation. Receptors incorporating p.P230S (which is heterozygous with p.R65W) desensitized much faster than wild type receptors and represent a new TM1 site capable of modulating desensitization. The recessive mutations p.R72C, p.R218W, p.L291P, p.D388A, and p.E375X precluded cell surface expression unless co-expressed with α1 wild type subunits. The recessive p.E375X mutation resulted in subunit truncation upstream of the TM4 domain. Surprisingly, on the basis of three independent assays, we were able to infer that p.E375X truncated subunits are incorporated into functional hGlyRs together with unmutated α1 or α1 plus ß subunits. These aberrant receptors exhibit significantly reduced glycine sensitivity. To our knowledge, this is the first suggestion that subunits lacking TM4 domains might be incorporated into functional pentameric ligand-gated ion channel receptors.

Urgencias en trastornos del movimiento que cursan con rigidez / Movement disorder emergencies accompanied by rigidity

Introducción. En el año 2002 se definieron las urgencias en trastornos del movimiento como cualquier trastorno neurológico, agudo o subagudo, en el que la presentación clínica está dominada por un trastorno del movimiento primario, y donde un fallo en el diagnóstico precoz puede resultar en una morbimortalidad importante. En este trabajo se revisarán aquellas urgencias en trastornos del movimiento que cursan con rigidez. En primer lugar las distonías agudas, siguiendo con el Síndrome Neuroléptico Maligno y por último una miscelánea de patologías. Objetivo. Revisar los avances más notorios publicados en la literatura científica en los últimos años en aquellas patologías que cursan con rigidez. Desarrollo. Se ha revisado la literatura de los últimos años y se presentan los avances más significativos en la patogenia, diagnóstico, y tratamiento, así como las principales perspectivas futuras en dichos campos (AU)

Introduction. In 2002 movement disorder emergencies were defined as any neurological disorder, either acute or subacute, in which the clinical presentation is dominated by a primary movement disorder, and where misdiagnosis in the early stages can result in important morbidity and mortality rates. This work reviews those movement disorder emergencies that are accompanied by rigidity. These are considered in the following order: first, acute dystonias, followed by neuroleptic malignant syndrome and, lastly, an assortment of other pathologies. Aims. The purpose of this study is to review the most significant advances in pathologies accompanied by rigidity that have recently been reported in the scientific literature. Development. The literature from the last few years was reviewed and we present the most significant advances in pathogenesis, diagnosis and treatment, as well as the main future perspectives in those fields (AU)

Function of hyperekplexia-causing α1R271Q/L glycine receptors is restored by shifting the affected residue out of the allosteric signalling pathway.

BACKGROUND AND PURPOSE Glycine receptor α1 subunit R271Q and R271L (α1R271Q/L) mutations cause the neuromotor disorder, hereditary hyperekplexia. Studies suggest that the 271 residue is located within the allosteric signalling pathway linking the agonist binding site to the channel gate. The present study aimed to investigate a possible mechanism for restoring the function of the α1R271Q/L glycine receptor. EXPERIMENTAL APPROACH A 12-amino-acid segment incorporating the 271 residue on the glycine receptor α1271Q/L subunit was replaced by the homologous segment from the glycine receptor ß subunit (α1(Ch) 271Q/L). The function of the α1(Ch) 271Q/L glycine receptor was examined by whole-cell patch-clamp recording and voltage-clamp fluorometry techniques. KEY RESULTS The function of the α1(Ch) 271Q/L glycine receptor was restored to the level of the wild-type (WT) α1 glycine receptor. Moreover, in the α1(Ch) glycine receptor, in contrast to the α1 glycine receptor, the channel function was not sensitive to various substitutions of the 271 residue, and the conformational change in the vicinity of the 271 residue was uncoupled from the channel gating. CONCLUSIONS AND IMPLICATIONS The 271 residue is shifted out of the allosteric signalling pathway in the α1(Ch) glycine receptor. We propose that this mechanism provides a novel drug design strategy not only for glycine receptor α1R271Q/L-caused hereditary hyperekplexia, but also for any pathological condition that is caused by missense mutation- or covalent modification-induced disorders involving residues in allosteric signalling pathways. Such a strategy makes it possible to design an ideal drug, which only corrects the function of the mutant or modified protein without affecting the WT or naive protein.

Allosteric modulators can restore function in an amino acid neurotransmitter receptor by slightly altering intra-molecular communication pathways.

Mutations, even if not directly in the ligand binding sites of proteins, can lead to disease. In cell surface receptors, this can happen if they uncouple conformational changes that take place upon agonist (or antagonist) binding to the extracellular domain and the intracellular response. Uncoupling can take place by disrupting a major allosteric propagation pathway between the extra- and intracellular domains. Here I provide a mechanistic explanation: I first describe how propagation takes place; second, what can happen in the presence of a disease-related mutation which is distant from the binding site; and finally, how drugs may overcome this disruption and rescue function. The mutations in the glycine receptor α1 subunit (α1R271Q/L) which cause the neuromotor disorder hyperekplexia are on example of such allosteric mutations. In this issue of the BJP, Shan et al. show that normal function was restored to these mutant receptors by substitution of the segment which contained the mutated position, by a homologous one. An allosteric drug could mimic the effects of such substitution. Within this framework, I highlight the advantages of allosteric drugs and the challenges in their design.

Exaggerated startle reactions.

The origin of the startle reflex lies in the caudal brainstem; it can be elicited by an unexpected stimulus resulting in a bilateral activation of many muscles. Two subsequent responses can be measured during EMG recordings; after the initial motor reflex, lasting until about 150 ms, a second response can occur. The second response contains more emotional and voluntary behavioral responses. Clinically, syndromes with hyperstartling as common feature can be divided into three groups: hyperekplexia, stimulus-induced disorders, and neuropsychiatric disorders. Classification of startle syndromes within these three groups remains challenging. Generalized stiffness at birth, excessive startling and temporary generalized stiffness after being startled point towards hyperekplexia. Stimulus-induced disorders are distinguished by careful clinical and neurophysiological evaluation, including video recordings. Neuropsychiatric disorders usually have additional behavioural and psychiatric symptoms. Polymyographic EMG startle recordings exhibit an exaggeration of the initial motor startle reflex in hyperekplexia, while neuropsychiatric startle syndromes demonstrate a variable response pattern and abnormal behavioural features. Neurophysiological investigation of the startle reflex can help to further delineate between the startle syndromes and unravel the aetiology of neuropsychiatric startle disorders.

Novel mutation in GLRB in a large family with hereditary hyperekplexia.

Hereditary hyperekplexia (HH) is a disorder of the inhibitory glycinergic neurotransmitter system. Mutations in five genes have been reported to cause the disease. However, only single mutation in GLRB, the gene encoding beta-subunit of the glycine receptor, in a singleton patient with HH has been found to date. In this study, 13 patients with HH were identified through neurology and genetic clinics. Formal clinical examinations, linkage analysis, homozygosity mapping, in-mutation screening of GLRB and in silico functional analyses were carried out. A novel mutation in GLRB among nine patients was identified. This c.596 T>G perturbation results in the change of the highly conserved methionine at position 177 to arginine. Besides the classical HH phenotype, seven patients had esotropia and few of them had behavioral problems. This study presents a large family with HH as a result of homozygous mutation in GLRB and expands the clinical spectrum of HH to include eye misalignment disorder. Moreover, the report of these familial cases supports the previous evidence in a single patient of an autosomal recessive inheritance of HH because of defects in GLRB.

"Stiff neonate" with mitochondrial DNA depletion and secondary neurotransmitter defects.

Mitochondrial disorders comprise a heterogenous group. A neonate who presented with episodes of severe truncal hypertonia and apnea progressed to a hypokinetic rigid syndrome characterized by hypokinesia, tremulousness, profound head lag, absent suck and gag reflexes, brisk deep tendon reflexes, ankle and jaw clonus, and evidence of autonomic dysfunction. Analysis of cerebrospinal fluid neurotransmitters from age 7 weeks demonstrated low levels of amine metabolites (homovanillic acid and 5-hydroxyindoleacetic acid), tetrahydrobiopterin, and pyridoxal phosphate. Mitochondrial DNA quantitative studies on muscle homogenate demonstrated a mitochondrial DNA depletion disorder. Respiratory chain enzymology demonstrated decreased complex IV activity. Screening for mitochondrial DNA rearrangement disorders and sequencing relevant mitochondrial genes produced negative results. No clinical or biochemical response to treatment with pyridoxal phosphate, tetrahydrobiopterin, or l-dopa occurred. The clinical course was progressive, and the patient died at age 19 months. Mitochondrial disorders causing secondary neurotransmitter diseases are usually severe, but are rarely reported. This diagnosis should be considered in neonates or infants who present with hypertonia, hypokinesia rigidity, and progressive neurodegeneration.

A novel movement disorder in related male Labrador Retrievers characterized by extreme generalized muscular stiffness.

OBJECTIVES: To describe the clinical phenotype of a new motor disorder in Labrador Retrievers. ANIMALS AND METHODS: Case series study. Seven young male Labrador Retrievers presented for evaluation of stiff gait. RESULTS: All affected dogs had generalized muscular stiffness, persistent at rest and resulting in restricted joint movements. They showed a forward flexed posture, festinating gait, and bradykinesia. Signs developed between 2 and 16 months of age and tended to stabilize in adulthood. Needle electromyogram in the conscious state showed continuous motor unit activity in resting epaxial and proximal limb muscles. This activity was abolished by general anesthesia. Muscle and nerve histopathology was normal. In 2 dogs necropsied, astrocytosis was evident throughout the spinal cord gray matter, reticular formation and caudate nuclei. Decreased neuronal counts were selectively found in the spinal cord Rexed's lamina VII, but not in VIII and IX. Pedigree analysis showed that the affected dogs were from 5 related litters. CONCLUSIONS AND CLINICAL IMPORTANCE: This new hypertonicity syndrome in Labrador Retrievers is unique because of the selective distribution of the histological lesions, the lack of progression in adulthood, and its exclusive occurrence in male dogs. Pedigree analysis suggests an X-linked hereditary disease, although other modes of inheritance cannot be ruled out with certainty. We hypothesize that altered output from basal nuclei and reticular formation together with motor neuron disinhibition caused by a decreased number of spinal cord interneurons leads to the muscular stiffness.

Mitochondrial transfer RNA(Phe) mutation associated with a progressive neurodegenerative disorder characterized by psychiatric disturbance, dementia, and akinesia-rigidity.

BACKGROUND: Mitochondrial diseases are characterized by wide phenotypic and genetic variability, but presentations in adults with akinetic rigidity and hyperkinetic movement disorders are rare. OBJECTIVES: To describe clinically a subject with progressive neurodegeneration characterized by psychosis, dementia, and akinesia-rigidity, and to associate this phenotype with a novel mitochondrial transfer RNA(Phe) (tRNA(Phe)) (MTTF) mutation. DESIGN, SETTING, AND PATIENT: Case description and detailed laboratory investigations of a 57-year-old woman at a university teaching hospital and a specialist mitochondrial diagnostic laboratory. RESULTS: Histopathological findings indicated that an underlying mitochondrial abnormality was responsible for the subject's progressive neurological disorder, with mitochondrial genome sequencing revealing a novel m.586G>A MTTF mutation. CONCLUSIONS: The clinical phenotypes associated with mitochondrial disorders may include akinesia-rigidity and psychosis. Our findings further broaden the spectrum of neurological disease associated with mitochondrial tRNA(Phe) mutations.