Variants in ATP5F1B are associated with dominantly inherited dystonia.

ATP5F1B is a subunit of the mitochondrial ATP synthase or complex V of the mitochondrial respiratory chain. Pathogenic variants in nuclear genes encoding assembly factors or structural subunits are associated with complex V deficiency, typically characterized by autosomal recessive inheritance and multisystem phenotypes. Movement disorders have been described in a subset of cases carrying autosomal dominant variants in structural subunits genes ATP5F1A and ATP5MC3. Here, we report the identification of two different ATP5F1B missense variants (c.1000A>C; p.Thr334Pro and c.1445T>C; p.Val482Ala) segregating with early-onset isolated dystonia in two families, both with autosomal dominant mode of inheritance and incomplete penetrance. Functional studies in mutant fibroblasts revealed no decrease of ATP5F1B protein amount but severe reduction of complex V activity and impaired mitochondrial membrane potential, suggesting a dominant-negative effect. In conclusion, our study describes a new candidate gene associated with isolated dystonia and confirms that heterozygous variants in genes encoding subunits of the mitochondrial ATP synthase may cause autosomal dominant isolated dystonia with incomplete penetrance, likely through a dominant-negative mechanism.

Rapidly progressive multiple system atrophy in a patient carrying LRRK2 G2019S mutation.

BACKGROUND: Multiple system atrophy (MSA) is considered a primarily sporadic neurodegenerative disease, but the role of genetic is poorly understood. CASE: We present a female patient of Moroccan origin who developed a rapidly progressive non-levodopa responsive parkinsonism, gait and balance problems, and dysautonomia including severe bulbar symptoms. She was diagnosed with MSA Parkinsonian-type (MSA-P) and suddenly died at night at 58 years of age. Reduced striatal DAT-SPECT, putaminal hyperintensity on T2-MRI, and hypometabolism with FDG-PET were present. Genetic testing documented a G2019S mutation in the LRRK2 gene. A skin biopsy was obtained and used to perform alpha-synuclein RT-QuIC, which was negative, and immunohistochemical analysis, which demonstrated abnormal alpha-synuclein deposits in cutaneous nerves. Elevated blood neurofilament light chain levels were also documented. CONCLUSIONS: LRRK2 mutations are the most common cause of monogenic Parkinson's disease (PD) and G2019S is the most frequent variant. Our patient presented with biological, clinical, and radiological features of MSA, but genetic testing revealed a G2019S LRRK2 mutation, which has been previously reported only in one other case of pathologically proven MSA but with mild progression. In our patient, post-mortem confirmation could not be performed, but RT-QuIC and immunohistochemical findings on skin biopsy support the diagnosis of MSA. G2019S LRRK2 may be linked to an increased risk of MSA. Cases of atypical parkinsonism with rapid disease course should be screened for PD-related genes especially in populations with a high prevalence of mutations in known genes.

Duodenal alpha-Synuclein Pathology and Enteric Gliosis in Advanced Parkinson's Disease.

BACKGROUND: The role of the gut-brain axis has been recently highlighted as a major contributor to Parkinson's disease (PD) physiopathology, with numerous studies investigating bidirectional transmission of pathological protein aggregates, such as α-synuclein (αSyn). However, the extent and the characteristics of pathology in the enteric nervous system have not been fully investigated. OBJECTIVE: We characterized αSyn alterations and glial responses in duodenum biopsies of patients with PD by employing topography-specific sampling and conformation-specific αSyn antibodies. METHODS: We examined 18 patients with advanced PD who underwent Duodopa percutaneous endoscopic gastrostomy and jejunal tube procedure, 4 untreated patients with early PD (disease duration <5 years), and 18 age- and -sex-matched healthy control subjects undergoing routine diagnostic endoscopy. A mean of four duodenal wall biopsies were sampled from each patient. Immunohistochemistry was performed for anti-aggregated αSyn (5G4) and glial fibrillary acidic protein antibodies. Morphometrical semiquantitative analysis was performed to characterize αSyn-5G4+ and glial fibrillary acidic protein-positive density and size. RESULTS: Immunoreactivity for aggregated α-Syn was identified in all patients with PD (early and advanced) compared with controls. αSyn-5G4+ colocalized with neuronal marker ß-III-tubulin. Evaluation of enteric glial cells demonstrated an increased size and density when compared with controls, suggesting reactive gliosis. CONCLUSIONS: We found evidence of synuclein pathology and gliosis in the duodenum of patients with PD, including early de novo cases. Future studies are required to evaluate how early in the disease process duodenal pathology occurs and its possible contribution to levodopa effect in chronic patients. © 2023 The Authors. Movement Disorders published by Wiley Periodicals LLC on behalf of International Parkinson and Movement Disorder Society.

Clinical, cognitive, and morphometric profiles of progressive supranuclear palsy phenotypes.

The International Parkinson's and Movement Disorder Society (MDS) criteria for progressive supranuclear palsy (PSP) have broadened the clinical spectrum of the disease and established phenotypic characterization according to the predominant manifestation at onset. The objective of this study is to describe clinical/cognitive and imaging features of a monocentric cohort of PSP patients, highlighting different patterns of functional disability according to the assigned phenotype. We retrospectively reviewed clinical/imaging data of 53 PSP patients diagnosed with probable PSP according to the MDS criteria and 40 age/sex-matched healthy controls (HCs). Neurological/neuropsychological assessments were performed using standardized scales, as well as comprehensive magnetic resonance imaging (MRI) morphometric measurements. In our cohort, there were 24/53 PSP-RS (Richardson's syndrome), 13/53 PSP-P (Parkinsonism), 7/53 PSP-PGF (Progressive gait freezing), and 9/53 PSP-Cog (Cognitive impairment). PSP-Cog presented the worst motor profiles, the highest percentages of dementia and impaired functional autonomy; 4/9 PSP-Cog and 2/7 PSP-PGF died. PSP-P had the lowest motor/cognitive burden. All MRI parameters had good discriminative efficacy vs. HCs, with P/M 2.0 discriminating PSP-PGF from PSP-RS and PSP-Cog. We highlighted discrete clinical and imaging patterns that best characterize different PSP phenotypes. PSP-Cog and PSP-PGF/RS manifest greater incidence of dementia and motor disability, respectively, while PSP-P has a more benign course. The identification of different phenotypes may be the expression of different progression patterns requiring tailored approaches in terms of follow-up and treatment. These findings support the concept of discrete patterns of Tau pathology within the PSP spectrum and encourage research for phenotype-specific outcome measures.

Caspr1 antibodies autoimmune paranodopathy with severe tetraparesis: Potential relevance of antibody titers in monitoring treatment response.

AIM: Nodopathies and paranodopathies are autoimmune neuropathies associated with antibodies to nodal-paranodal antigens (neurofascin 140/186 and 155, contactin-1, contactin-associated protein 1 [Caspr1]) characterized by peculiar clinical features, poor response to standard immunotherapies (e.g., intravenous immunoglobulins, IVIg). Improvement after anti-CD20 monoclonal antibody therapy has been reported. Data on Caspr1 antibodies pathogenicity are still preliminary, and longitudinal titers have been poorly described. METHODS: We report on a young woman who developed a disabling neuropathy with antibodies to the Caspr1/contactin-1 complex showing a dramatic improvement after rituximab therapy, mirrored by the decrease of antibody titers. RESULTS: A 26-year-old woman presented with ataxic-stepping gait, severe motor weakness at four limbs, and low frequency postural tremor. For neurophysiological evidence of demyelinating neuropathy, she was diagnosed with chronic inflammatory demyelinating polyradiculoneuropathy and treated with IVIg without benefit. MRI showed symmetrical hypertrophy and marked signal hyperintensity of brachial and lumbosacral plexi. Cerebrospinal fluid showed 710 mg/dL protein. Despite intravenous methylprednisolone, the patient progressively worsened, and became wheelchair-bound. Antibodies to nodal-paranodal antigens were searched for by ELISA and cell-based assay. Anticontactin/Caspr1 IgG4 antibodies resulted positive. The patient underwent rituximab therapy with slow progressive improvement that mirrored the antibodies titer, measured throughout the disease course. CONCLUSIONS: Our patient had a severe progressive course with early disability and axonal damage, and slow recovery starting only a few months after antibody-depleting therapy. The close correlation between titer, disability, and treatment, supports the pathogenicity of Caspr1 antibodies, and suggest that their longitudinal evaluation might provide a potential biomarker to evaluate treatment response.

EIF2AK2 Missense Variants Associated with Early Onset Generalized Dystonia.

OBJECTIVE: The study was undertaken to identify a monogenic cause of early onset, generalized dystonia. METHODS: Methods consisted of genome-wide linkage analysis, exome and Sanger sequencing, clinical neurological examination, brain magnetic resonance imaging, and protein expression studies in skin fibroblasts from patients. RESULTS: We identified a heterozygous variant, c.388G>A, p.Gly130Arg, in the eukaryotic translation initiation factor 2 alpha kinase 2 (EIF2AK2) gene, segregating with early onset isolated generalized dystonia in 5 patients of a Taiwanese family. EIF2AK2 sequencing in 191 unrelated patients with unexplained dystonia yielded 2 unrelated Caucasian patients with an identical heterozygous c.388G>A, p.Gly130Arg variant, occurring de novo in one case, another patient carrying a different heterozygous variant, c.413G>C, p.Gly138Ala, and one last patient, born from consanguineous parents, carrying a third, homozygous variant c.95A>C, p.Asn32Thr. These 3 missense variants are absent from gnomAD, and are located in functional domains of the encoded protein. In 3 patients, additional neurological manifestations were present, including intellectual disability and spasticity. EIF2AK2 encodes a kinase (protein kinase R [PKR]) that phosphorylates eukaryotic translation initiation factor 2 alpha (eIF2α), which orchestrates the cellular stress response. Our expression studies showed abnormally enhanced activation of the cellular stress response, monitored by PKR-mediated phosphorylation of eIF2α, in fibroblasts from patients with EIF2AK2 variants. Intriguingly, PKR can also be regulated by PRKRA (protein interferon-inducible double-stranded RNA-dependent protein kinase activator A), the product of another gene causing monogenic dystonia. INTERPRETATION: We identified EIF2AK2 variants implicated in early onset generalized dystonia, which can be dominantly or recessively inherited, or occur de novo. Our findings provide direct evidence for a key role of a dysfunctional eIF2α pathway in the pathogenesis of dystonia. ANN NEUROL 2021;89:485-497.

Diagnostic and therapeutic recommendations in adult dystonia: a joint document by the Italian Society of Neurology, the Italian Academy for the Study of Parkinson's Disease and Movement Disorders, and the Italian Network on Botulinum Toxin.

The diagnostic framework and the therapeutic management of patients with adult dystonia can represent a challenge for clinical neurologists. The objective of the present paper is to delineate diagnostic and therapeutic recommendations for dystonia provided by a panel of Italian experts afferent to the Italian Society of Neurology, the Italian Academy for the Study of Parkinson's Disease and Movement Disorders, and the Italian Network on Botulinum Toxin. We first discuss the clinical approach and the instrumental assessment useful for diagnostic purpose. Then, we analyze the pharmacological, surgical, and rehabilitative therapeutic options for adult dystonia. Finally, we propose a hospital-territory network model for adult dystonia management.

Expanding the genetic spectrum of primary familial brain calcification due to SLC2OA2 mutations: a case series.

Primary familial brain calcification (PFBC) is a neurological condition characterized by the presence of intracranial calcifications, mainly involving basal ganglia, thalamus, and dentate nuclei. So far, six genes have been linked to this condition: SLC20A2, PDGFRB, PDGFB, and XPR1 inherited as autosomal-dominant trait, while MYORG and JAM2 present a recessive pattern of inheritance. Patients mainly present with movement disorders, psychiatric disturbances, and cognitive decline or are completely asymptomatic and calcifications may represent an occasional finding. Here we present three variants in SLC20A2, two exonic and one intronic, which we found in patients with PFBC associated to three different clinical phenotypes. One variant is novel and two were already described as variants of uncertain significance. We confirm the pathogenicity of these three variants and suggest a broadening of the phenotypic spectrum associated with mutations in SLC20A2.

Impact of social and mobility restrictions in Parkinson's disease during COVID-19 lockdown.

BACKGROUND: The consequences of strict COVID-19 mobility restrictions on motor/non-motor features in Parkinson's disease (PD) have not been systematically studied but worse mobility and quality of life have been reported. To elucidate this question, 12 mild to moderate PD patients were assessed in March 2020 before and after two months of isolation as part of a clinical study that had to be interrupted due to the pandemic and the implementation of COVID19 mobility restrictions. METHODS: Twelve patients were systematically evaluated before and after the lockdown period as part of a larger cohort that previously underwent thermal water rehabilitation. Clinical outcomes were the Body Mass index, the Mini-Balance Evaluation Systems Test, the MDS-Unified Parkinson's Disease Rating Scale part III, the 6 Minute Walking Test and the New Freezing of Gait Questionnaire. Global cognition was evaluated with the Montreal Cognitive Assessment scale. The impact of COVID-19 restrictions on quality of life and functional independence was evaluated with The Parkinson's disease Quality of life (PDQ-39), the Activities of Daily Living (ADL) and Instrumental Activities of Daily Living questionnaires (IADL) and the Parkinson's disease cognitive functional rating scales (PD-CFRS). RESULTS: After two months of isolation the Mini-BESTest score worsened (p=0.005), and four patients reported one or more falls during the lockdown. BMI increased (p=0.031) while the remaining clinical variables including quality of life did not change. CONCLUSION: We observed moderate worsening at Mini-BESTest, greater risk of falls and increased body weight as consequence of prolonged immobility. We believe negative effects were partially softened since patients were in contact with our multidisciplinary team during the lockdown and had previously received training to respond to the needs of this emergency isolation. These findings highligh the importnace of patient-centered interventions in PD management.

Harmful Iron-Calcium Relationship in Pantothenate kinase Associated Neurodegeneration.

Pantothenate Kinase-associated Neurodegeneration (PKAN) belongs to a wide spectrum of diseases characterized by brain iron accumulation and extrapyramidal motor signs. PKAN is caused by mutations in PANK2, encoding the mitochondrial pantothenate kinase 2, which is the first enzyme of the biosynthesis of Coenzyme A. We established and characterized glutamatergic neurons starting from previously developed PKAN Induced Pluripotent Stem Cells (iPSCs). Results obtained by inductively coupled plasma mass spectrometry indicated a higher amount of total cellular iron in PKAN glutamatergic neurons with respect to controls. PKAN glutamatergic neurons, analyzed by electron microscopy, exhibited electron dense aggregates in mitochondria that were identified as granules containing calcium phosphate. Calcium homeostasis resulted compromised in neurons, as verified by monitoring the activity of calcium-dependent enzyme calpain1, calcium imaging and voltage dependent calcium currents. Notably, the presence of calcification in the internal globus pallidus was confirmed in seven out of 15 genetically defined PKAN patients for whom brain CT scan was available. Moreover, we observed a higher prevalence of brain calcification in females. Our data prove that high amount of iron coexists with an impairment of cytosolic calcium in PKAN glutamatergic neurons, indicating both, iron and calcium dys-homeostasis, as actors in pathogenesis of the disease.

Spasmodic dysphonia as a presenting symptom of spinocerebellar ataxia type 12.

Autosomal dominant spinocerebellar ataxia (SCA) type 12 is a rare SCA characterized by a heterogeneous phenotype. Action tremor of the upper limbs is the most common presenting sign and cerebellar signs can appear subsequently. In many cases, minor signs, like dystonia, can be predominant even at onset. Laryngeal dystonia (spasmodic dysphonia) has been observed only in one case of SCA12 and never reported at disease onset. We present a 61-year-old female who developed spasmodic dysphonia followed by dystonic tremor and subsequent ataxia diagnosed with SCA12. Thus, spasmodic dysphonia can be a presenting symptom of SCA12.

De Novo Mutations in PDE10A Cause Childhood-Onset Chorea with Bilateral Striatal Lesions.

Chorea is a hyperkinetic movement disorder resulting from dysfunction of striatal medium spiny neurons (MSNs), which form the main output projections from the basal ganglia. Here, we used whole-exome sequencing to unravel the underlying genetic cause in three unrelated individuals with a very similar and unique clinical presentation of childhood-onset chorea and characteristic brain MRI showing symmetrical bilateral striatal lesions. All individuals were identified to carry a de novo heterozygous mutation in PDE10A (c.898T>C [p.Phe300Leu] in two individuals and c.1000T>C [p.Phe334Leu] in one individual), encoding a phosphodiesterase highly and selectively present in MSNs. PDE10A contributes to the regulation of the intracellular levels of cyclic adenosine monophosphate (cAMP) and cyclic guanosine monophosphate (cGMP). Both substitutions affect highly conserved amino acids located in the regulatory GAF-B domain, which, by binding to cAMP, stimulates the activity of the PDE10A catalytic domain. In silico modeling showed that the altered residues are located deep in the binding pocket, where they are likely to alter cAMP binding properties. In vitro functional studies showed that neither substitution affects the basal PDE10A activity, but they severely disrupt the stimulatory effect mediated by cAMP binding to the GAF-B domain. The identification of PDE10A mutations as a cause of chorea further motivates the study of cAMP signaling in MSNs and highlights the crucial role of striatal cAMP signaling in the regulation of basal ganglia circuitry. Pharmacological modulation of this pathway could offer promising etiologically targeted treatments for chorea and other hyperkinetic movement disorders.

Recessive mutations in VPS13D cause childhood onset movement disorders.

VPS13 protein family members VPS13A through VPS13C have been associated with various recessive movement disorders. We describe the first disease association of rare recessive VPS13D variants including frameshift, missense, and partial duplication mutations with a novel complex, hyperkinetic neurological disorder. The clinical features include developmental delay, a childhood onset movement disorder (chorea, dystonia, or tremor), and progressive spastic ataxia or paraparesis. Characteristic brain magnetic resonance imaging shows basal ganglia or diffuse white matter T2 hyperintensities as seen in Leigh syndrome and choreoacanthocytosis. Muscle biopsy in 1 case showed mitochondrial aggregates and lipidosis, suggesting mitochondrial dysfunction. These findings underline the importance of the VPS13 complex in neurological diseases and a possible role in mitochondrial function. Ann Neurol 2018;83:1089-1095.

Frequency and phenotypic spectrum of KMT2B dystonia in childhood: A single-center cohort study.

BACKGROUND: Childhood-onset dystonia is often genetically determined. Recently, KMT2B variants have been recognized as an important cause of childhood-onset dystonia. OBJECTIVE: To define the frequency of KMT2B mutations in a cohort of dystonic patients aged <18 years at onset, the associated clinical and radiological phenotype, and the natural history of disease. METHODS: Whole-exome sequencing or customized gene panels were used to screen a cohort of 65 patients who had previously tested negative for all other known dystonia-associated genes. RESULTS: We identified 14 patients (21.5%) carrying KMT2B variants, of which 1 was classified as a variant of unknown significance. We also identified 2 additional patients carrying pathogenic mutations in GNAO1 and ATM. Overall, we established a definitive genetic diagnosis in 23% of cases. We observed a spectrum of clinical manifestations in KMT2B variant carriers, ranging from generalized dystonia to short stature or intellectual disability alone, even within the same family. In 78.5% of cases, dystonia involved the lower limbs at onset, with later caudocranial generalization. Eight patients underwent pallidal DBS with a median decrease of Burke-Fahn-Marsden Dystonia Rating Scale-Motor score of 38.5% in the long term. We also report on 4 asymptomatic carriers, suggesting that some KMT2B mutations may be associated with incomplete disease penetrance. CONCLUSIONS: KMT2B mutations are frequent in childhood-onset dystonia and cause a complex neurodevelopmental syndrome, often featuring growth retardation and intellectual disability as additional phenotypic features. A dramatic and long-lasting response to DBS is characteristic of DYT-KMT2B dystonia. © 2019 International Parkinson and Movement Disorder Society.

Long-term effect of subthalamic and pallidal deep brain stimulation for status dystonicus in children with methylmalonic acidemia and GNAO1 mutation.

Status dystonicus (SD) is a rare and potentially life-threatening condition requiring intensive care management. Deep brain stimulation (DBS) has emerged as an effective treatment for SD refractory to medical management, but its application in this field is still limited. Here, we report the long-term outcome of four pediatric patients treated with DBS at the University Hospital of Padua, Italy, for SD refractory to medications. In addition, we present the results of a systematic literature review aimed at identifying published cases of SD treated with DBS, with focus on motor outcome. In our cohort, two children were affected by methylmalonic acidemia and suffered acute basal ganglia lesions, while the other two carried a pathogenic mutation in GNAO1 gene. DBS target was subthalamic nucleus (STN) in one case and globus pallidus internus (GPi) in three. All patients experienced SD resolution within 8-19 days after surgery. Mean post-operative follow-up was 5 years. We identified in the literature 53 additional SD cases treated with DBS (median age at DBS implantation: 12 years) with reported positive outcome in 51 and resolution of SD in a mean of 17 days after surgery. Our findings indicate that DBS is an effective treatment for SD refractory to medications, even in patients with acute basal ganglia lesions; STN can be an appropriate target when GPi is damaged. Moreover, data from long-term follow-up show that SD recurrences can be significantly reduced in frequency or abolished after DBS implantation.

Inborn errors of coenzyme A metabolism and neurodegeneration.

Two inborn errors of coenzyme A (CoA) metabolism are responsible for distinct forms of neurodegeneration with brain iron accumulation (NBIA), a heterogeneous group of neurodegenerative diseases having as a common denominator iron accumulation mainly in the inner portion of globus pallidus. Pantothenate kinase-associated neurodegeneration (PKAN), an autosomal recessive disorder with progressive impairment of movement, vision and cognition, is the most common form of NBIA and is caused by mutations in the pantothenate kinase 2 gene (PANK2), coding for a mitochondrial enzyme, which phosphorylates vitamin B5 in the first reaction of the CoA biosynthetic pathway. Another very rare but similar disorder, denominated CoPAN, is caused by mutations in coenzyme A synthase gene (COASY) coding for a bi-functional mitochondrial enzyme, which catalyzes the final steps of CoA biosynthesis. It still remains a mystery why dysfunctions in CoA synthesis lead to neurodegeneration and iron accumulation in specific brain regions, but it is now evident that CoA metabolism plays a crucial role in the normal functioning and metabolism of the nervous system.

Partial loss-of-function of sodium channel SCN8A in familial isolated myoclonus.

Variants in the neuronal sodium channel gene SCN8A have been implicated in several neurological disorders. Early infantile epileptic encephalopathy type 13 results from de novo gain-of-function mutations that alter the biophysical properties of the channel. Complete loss-of-function variants of SCN8A have been identified in cases of isolated intellectual disability. We now report a novel heterozygous SCN8A variant, p.Pro1719Arg, in a small pedigree with five family members affected with autosomal dominant upper limb isolated myoclonus without seizures or cognitive impairment. Functional analysis of the p.Pro1719Arg variant in transfected neuron-derived cells demonstrated greatly reduced Nav 1.6 channel activity without altered gating properties. Hypomorphic alleles of Scn8a in the mouse are known to result in similar movement disorders. This study expands the phenotypic and functional spectrum of SCN8A variants to include inherited nonepileptic isolated myoclonus. SCN8A can be considered as a candidate gene for isolated movement disorders without seizures.

A missense mutation in KCTD17 causes autosomal dominant myoclonus-dystonia.

Myoclonus-dystonia (M-D) is a rare movement disorder characterized by a combination of non-epileptic myoclonic jerks and dystonia. SGCE mutations represent a major cause for familial M-D being responsible for 30%-50% of cases. After excluding SGCE mutations, we identified through a combination of linkage analysis and whole-exome sequencing KCTD17 c.434 G>A p.(Arg145His) as the only segregating variant in a dominant British pedigree with seven subjects affected by M-D. A subsequent screening in a cohort of M-D cases without mutations in SGCE revealed the same KCTD17 variant in a German family. The clinical presentation of the KCTD17-mutated cases was distinct from the phenotype usually observed in M-D due to SGCE mutations. All cases initially presented with mild myoclonus affecting the upper limbs. Dystonia showed a progressive course, with increasing severity of symptoms and spreading from the cranio-cervical region to other sites. KCTD17 is abundantly expressed in all brain regions with the highest expression in the putamen. Weighted gene co-expression network analysis, based on mRNA expression profile of brain samples from neuropathologically healthy individuals, showed that KCTD17 is part of a putamen gene network, which is significantly enriched for dystonia genes. Functional annotation of the network showed an over-representation of genes involved in post-synaptic dopaminergic transmission. Functional studies in mutation bearing fibroblasts demonstrated abnormalities in endoplasmic reticulum-dependent calcium signaling. In conclusion, we demonstrate that the KCTD17 c.434 G>A p.(Arg145His) mutation causes autosomal dominant M-D. Further functional studies are warranted to further characterize the nature of KCTD17 contribution to the molecular pathogenesis of M-D.