Insights into Ancestral Diversity in Parkinsons Disease Risk: A Comparative Assessment of Polygenic Risk Scores

Objectives To evaluate and compare different polygenic risk score (PRS) models in predicting Parkinsons disease (PD) across diverse ancestries, focusing on identifying the most suitable approach for each population and potentially contributing to equitable advancements in precision medicine. Methods We constructed a total of 105 PRS across individual level data from seven diverse ancestries. First, a cross-ancestry conventional PRS comparison was implemented by utilizing the 90 known European risk loci with weighted effects from four independent summary statistics including European, East Asian, Latino/Admixed American, and African/Admixed. These models were adjusted by sex, age, and principal components (28 PRS) and by sex, age, and percentage of admixture (28 PRS) for comparison. Secondly, a novel and refined multi-ancestry best-fit PRS approach was then applied across the seven ancestries by leveraging multi-ancestry meta-analyzed summary statistics and using a p-value thresholding approach (49 PRS) to enhance prediction applicability in a global setting. Results European-based PRS models predicted disease status across all ancestries to differing degrees of accuracy. Ashkenazi Jewish had the highest Odds Ratio (OR): 1.96 (95% CI: 1.69-2.25, p < 0.0001) with an AUC (Area Under the Curve) of 68%. Conversely, the East Asian population, despite having fewer predictive variants (84 out of 90), had an OR of 1.37 (95% CI: 1.32-1.42) and an AUC of 62%, illustrating the cross-ancestry transferability of this model. Lower OR alongside broader confidence intervals were observed in other populations, including Africans (OR =1.38, 95% CI: 1.12-1.63, p=0.001). Adjustment by percentage of admixture did not outperform principal components. Multi-ancestry best-fit PRS models improved risk prediction in European, Ashkenazi Jewish, and African ancestries, yet didn't surpass conventional PRS in admixed populations such as Latino/American admixed and African admixed populations. Interpretation The present study represents a novel and comprehensive assessment of PRS performance across seven ancestries in PD, highlighting the inadequacy of a 'one size fits all' approach in genetic risk prediction. We demonstrated that European based PD PRS models are partially transferable to other ancestries and could be improved by a novel best-fit multi-ancestry PRS, especially in non-admixed populations.

Genome sequence analyses identify novel risk loci for multiple system atrophy

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

Gene-Environment Interactions for Parkinson's Disease

OBJECTIVE

Parkinson's disease (PD) is a neurodegenerative disorder with complex etiology. Multiple genetic and environmental factors have been associated with PD, but most PD risk remains unexplained. The aim of this study was to test for statistical interactions between PD-related genetic and environmental exposures in the 23andMe, Inc. research dataset.

METHODS

Using a validated PD polygenic risk score and common PD-associated variants in the GBA gene, we explored interactions between genetic susceptibility factors and 7 lifestyle and environmental factors: body mass index (BMI), type 2 diabetes (T2D), tobacco use, caffeine consumption, pesticide exposure, head injury, and physical activity (PA).

RESULTS

We observed that T2D, as well as higher BMI, caffeine consumption, and tobacco use, were associated with lower odds of PD, whereas head injury, pesticide exposure, GBA carrier status, and PD polygenic risk score were associated with higher odds. No significant association was observed between PA and PD. In interaction analyses, we found statistical evidence for an interaction between polygenic risk of PD and the following environmental/lifestyle factors: T2D (p = 6.502 × 10-8), PA (p = 8.745 × 10-5), BMI (p = 4.314 × 10-4), and tobacco use (p = 2.236 × 10-3). Although BMI and tobacco use were associated with lower odds of PD regardless of the extent of individual genetic liability, the direction of the relationship between odds of PD and T2D, as well as PD and PA, varied depending on polygenic risk score.

INTERPRETATION

We provide preliminary evidence that associations between some environmental and lifestyle factors and PD may be modified by genotype. ANN NEUROL 2024;95:677-687.

Phenoconversion in pure autonomic failure: a multicentre prospective longitudinal cohort study

We aimed to describe the clinical features of patients with pure autonomic failure (PAF) preceding phenoconversion that could be useful as predictive markers for advancing α-synuclein-associated neurodegeneration of the brain. Patients diagnosed with PAF were evaluated at 8 Centers (7-US based and 1 European) and enrolled in a longitudinal observational cohort study (NCT01799915). Subjects underwent detailed assessments of motor, sleep, olfactory, cognitive, and autonomic function and were followed prospectively to determine whether they developed parkinsonism or dementia for up to 10 years. We identified incident cases of Parkinson disease (PD), dementia with Lewy bodies (DLB), or multiple system atrophy (MSA) and computed hazard ratios for phenoconversion as functions of clinical features. A total of 209 participants with PAF with a median disease duration of 6 years (IQR: 3-10) were enrolled. Of those, 149 provided follow-up information at an office or telemedicine visit. After a mean follow-up duration of 3 years, 48 (33%) participants phenoconverted (42% to PD, 35% to DLB, and 23% to MSA). Faster phenoconversion from study enrollment to any diagnosis was associated with urinary and sexual dysfunction [HR 5.9, 95%CI: 1.6-22, and HR: 3.6, 95%CI: 1.1-12] followed by subtle motor signs [HR: 2.7, 95%CI: 1.2-6], trouble swallowing [HR 2.5, 95%CI: 1.4-4.5], and changes in speech [HR:2.4, 95%CI:1.1-4.8] at enrollment. Subjects reporting deterioration of handwriting were more likely to phenoconvert to PD (HR: 2.6, 95%CI: 1.1-5.9, ) and those reporting difficulty handling utensils were more likely to phenoconvert to DLB (HR: 6.8, 95%CI: 1.2-38). Patients with a younger age of PAF onset [HR: 11, 95%CI: 2.6-46], preserved olfaction [HR: 8.7, 95%CI: 1.7-45], anhidrosis [HR: 1.8, 95%CI: 1-3.1, p=0.042], and severe urinary problems [HR 1.6, 95%CI: 1-2.5, p=0.033] were more likely to phenoconvert to MSA. The best autonomic predictor of PD was a blunted heart rate increase during the tilt-table test (HR: 6.1, 95%CI: 1.4-26). Patients with PAF have an estimated 12% (95% CI: 9%-15%) per year annual risk following study entry of phenoconverting to a manifest CNS synucleinopathy.

Height, weight, and body mass index in patients with familial dysautonomia

BACKGROUND

Children with familial dysautonomia (FD) are smaller and grow more slowly than the general population. It is unknown whether this abnormal growth is due to comorbidities that patients with FD live with, or if it is a direct effect of the disease-causing homozygous ELP-1 mutations. Here, we created growth curves for weight, height, and body mass index (BMI) in male and female children with FD to monitor the nutritional status of patients with FD.

METHODS

We used the New York University (NYU) FD Registry which includes data from 680 individuals with FD who were followed longitudinally since birth. We generated sex-specific FD growth charts for three age ranges (birth to 36 months, 2 to 20 years, and 2 to 40 years) and compared them to the general population. We generated Kaplan-Meier curves to test the hypothesis that FD patients with low BMI had shorter survival than the rest of the cohort.

RESULTS

Growth charts generated from 591 individuals with FD show that these patients grow more slowly, reach less height, and gain less weight than the general population. The impact of FD on height was more pronounced in girls than in boys. However, both groups showed markedly low weights, which resulted in low BMI. Low weight, but not height, is already evident at birth. In a subpopulation of FD patients, we found that treatment with growth hormone or spinal fusion surgery helped patients achieve the expected growth characteristic of FD patients, but these treatments did not lead FD patients to achieve the growth pattern of the general population. Contrary to our hypothesis, low BMI had no impact on patient survival.

CONCLUSIONS

Pediatric patients with FD have lower height, weight, and BMI compared to the general pediatric population, but this does not appear to affect survival. Growth curves specific to the FD population are an important tool to monitor growth and nutritional status in pediatric patients with FD when the general population growth curves are of limited use.

Identification of genetic risk loci and causal insights associated with Parkinson's disease in African and African admixed populations: a genome-wide association study

BACKGROUND

An understanding of the genetic mechanisms underlying diseases in ancestrally diverse populations is an important step towards development of targeted treatments. Research in African and African admixed populations can enable mapping of complex traits, because of their genetic diversity, extensive population substructure, and distinct linkage disequilibrium patterns. We aimed to do a comprehensive genome-wide assessment in African and African admixed individuals to better understand the genetic architecture of Parkinson's disease in these underserved populations.

METHODS

We performed a genome-wide association study (GWAS) in people of African and African admixed ancestry with and without Parkinson's disease. Individuals were included from several cohorts that were available as a part of the Global Parkinson's Genetics Program, the International Parkinson's Disease Genomics Consortium Africa, and 23andMe. A diagnosis of Parkinson's disease was confirmed clinically by a movement disorder specialist for every individual in each cohort, except for 23andMe, in which it was self-reported based on clinical diagnosis. We characterised ancestry-specific risk, differential haplotype structure and admixture, coding and structural genetic variation, and enzymatic activity.

FINDINGS

We included 197 918 individuals (1488 cases and 196 430 controls) in our genome-wide analysis. We identified a novel common risk factor for Parkinson's disease (overall meta-analysis odds ratio for risk of Parkinson's disease 1·58 [95% CI 1·37-1·80], p=2·397 × 10-14) and age at onset at the GBA1 locus, rs3115534-G (age at onset β=-2·00 [SE=0·57], p=0·0005, for African ancestry; and β=-4·15 [0·58], p=0·015, for African admixed ancestry), which was rare in non-African or non-African admixed populations. Downstream short-read and long-read whole-genome sequencing analyses did not reveal any coding or structural variant underlying the GWAS signal. The identified signal seems to be associated with decreased glucocerebrosidase activity.

INTERPRETATION

Our study identified a novel genetic risk factor in GBA1 in people of African ancestry, which has not been seen in European populations, and it could be a major mechanistic basis of Parkinson's disease in African populations. This population-specific variant exerts substantial risk on Parkinson's disease as compared with common variation identified through GWAS and it was found to be present in 39% of the cases assessed in this study. This finding highlights the importance of understanding ancestry-specific genetic risk in complex diseases, a particularly crucial point as the Parkinson's disease field moves towards targeted treatments in clinical trials. The distinctive genetics of African populations highlights the need for equitable inclusion of ancestrally diverse groups in future trials, which will be a valuable step towards gaining insights into novel genetic determinants underlying the causes of Parkinson's disease. This finding opens new avenues towards RNA-based and other therapeutic strategies aimed at reducing lifetime risk of Parkinson's disease.

FUNDING

The Global Parkinson's Genetics Program, which is funded by the Aligning Science Across Parkinson's initiative, and The Michael J Fox Foundation for Parkinson's Research.

Creating a data dictionary for pediatric autonomic disorders

PURPOSE

Whether evaluating patients clinically, documenting care in the electronic health record, performing research, or communicating with administrative agencies, the use of a common set of terms and definitions is vital to ensure appropriate use of language. At a 2017 meeting of the Pediatric Section of the American Autonomic Society, it was determined that an autonomic data dictionary comprising aspects of evaluation and management of pediatric patients with autonomic disorders would be an important resource for multiple stakeholders.

METHODS

Our group created the list of terms for the dictionary. Definitions were prioritized to be obtained from established sources with which to harmonize. Some definitions needed mild modification from original sources. The next tier of sources included published consensus statements, followed by Internet sources. In the absence of appropriate sources, we created a definition.

RESULTS

A total of 589 terms were listed and defined in the dictionary. Terms were organized by Signs/Symptoms, Triggers, Co-morbid Disorders, Family History, Medications, Medical Devices, Physical Examination Findings, Testing, and Diagnoses.

CONCLUSION

Creation of this data dictionary becomes the foundation of future clinical care and investigative research in pediatric autonomic disorders, and can be used as a building block for a subsequent adult autonomic data dictionary.

Familial dysautonomia

Familial dysautonomia (FD) is an autosomal recessive hereditary sensory and autonomic neuropathy (HSAN, type 3) expressed at birth with profound sensory loss and early death. The FD founder mutation in the ELP1 gene arose within the Ashkenazi Jews in the sixteenth century and is present in 1:30 Jews of European ancestry. The mutation yield a tissue-specific skipping of exon 20 and a loss of function of the elongator-1 protein (ELP1), which is essential for the development and survival of neurons. Patients with FD produce variable amounts of ELP1 in different tissues, with the brain producing mostly mutant transcripts. Patients have excessive blood pressure variability due to the failure of the IXth and Xth cranial nerves to carry baroreceptor signals. Neurogenic dysphagia causes frequent aspiration leading to chronic pulmonary disease. Characteristic hyperadrenergic "autonomic crises" consisting of brisk episodes of severe hypertension, tachycardia, skin blotching, retching, and vomiting occur in all patients. Progressive features of the disease include retinal nerve fiber loss and blindness, and proprioceptive ataxia with severe gait impairment. Chemoreflex failure may explain the high frequency of sudden death in sleep. Although 99.5% of patients are homozygous for the founder mutation, phenotypic severity varies, suggesting that modifier genes impact expression. Medical management is currently symptomatic and preventive. Disease-modifying therapies are close to clinical testing. Endpoints to measure efficacy have been developed, and the ELP1 levels are a good surrogate endpoint for target engagement. Early intervention may be critical for treatment to be successful.

Genome-wide Association Identifies Novel Etiological Insights Associated with Parkinson's Disease in African and African Admixed Populations

Background

Understanding the genetic mechanisms underlying diseases in ancestrally diverse populations is a critical step towards the realization of the global application of precision medicine. The African and African admixed populations enable mapping of complex traits given their greater levels of genetic diversity, extensive population substructure, and distinct linkage disequilibrium patterns.

Methods

Here we perform a comprehensive genome-wide assessment of Parkinson's disease (PD) in 197,918 individuals (1,488 cases; 196,430 controls) of African and African admixed ancestry, characterizing population-specific risk, differential haplotype structure and admixture, coding and structural genetic variation and polygenic risk profiling.

Findings

We identified a novel common risk factor for PD and age at onset at the GBA1 locus (risk, rs3115534-G; OR=1.58, 95% CI = 1.37 - 1.80, P=2.397E-14; age at onset, BETA =-2.004, SE =0.57, P = 0.0005), that was found to be rare in non-African/African admixed populations. Downstream short- and long-read whole genome sequencing analyses did not reveal any coding or structural variant underlying the GWAS signal. However, we identified that this signal mediates PD risk via expression quantitative trait locus (eQTL) mechanisms. While previously identified GBA1 associated disease risk variants are coding mutations, here we suggest a novel functional mechanism consistent with a trend in decreasing glucocerebrosidase activity levels. Given the high population frequency of the underlying signal and the phenotypic characteristics of the homozygous carriers, we hypothesize that this variant may not cause Gaucher disease. Additionally, the prevalence of Gaucher's disease in Africa is low.

Interpretation

The present study identifies a novel African-ancestry genetic risk factor in GBA1 as a major mechanistic basis of PD in the African and African admixed populations. This striking result contrasts to previous work in Northern European populations, both in terms of mechanism and attributable risk. This finding highlights the importance of understanding population-specific genetic risk in complex diseases, a particularly crucial point as the field moves toward precision medicine in PD clinical trials and while recognizing the need for equitable inclusion of ancestrally diverse groups in such trials. Given the distinctive genetics of these underrepresented populations, their inclusion represents a valuable step towards insights into novel genetic determinants underlying PD etiology. This opens new avenues towards RNA-based and other therapeutic strategies aimed at reducing lifetime risk.

Research in Context

Evidence Before this Study

Our current understanding of Parkinson's disease (PD) is disproportionately based on studying populations of European ancestry, leading to a significant gap in our knowledge about the genetics, clinical characteristics, and pathophysiology in underrepresented populations. This is particularly notable in individuals of African and African admixed ancestries. Over the last two decades, we have witnessed a revolution in the research area of complex genetic diseases. In the PD field, large-scale genome-wide association studies in the European, Asian, and Latin American populations have identified multiple risk loci associated with disease. These include 78 loci and 90 independent signals associated with PD risk in the European population, nine replicated loci and two novel population-specific signals in the Asian population, and a total of 11 novel loci recently nominated through multi-ancestry GWAS efforts.Nevertheless, the African and African admixed populations remain completely unexplored in the context of PD genetics.

Added Value of this Study

To address the lack of diversity in our research field, this study aimed to conduct the first genome-wide assessment of PD genetics in the African and African admixed populations. Here, we identified a genetic risk factor linked to PD etiology, dissected African-specific differences in risk and age at onset, characterized known genetic risk factors, and highlighted the utility of the African and African admixed risk haplotype substructure for future fine-mapping efforts. We identified a novel disease mechanism via expression changes consistent with decreased GBA1 activity levels. Future large scale single cell expression studies should investigate the neuronal populations in which expression differences are most prominent. This novel mechanism may hold promise for future efficient RNA-based therapeutic strategies such as antisense oligonucleotides or short interfering RNAs aimed at preventing and decreasing disease risk. We envisage that these data generated under the umbrella of the Global Parkinson's Genetics Program (GP2) will shed light on the molecular mechanisms involved in the disease process and might pave the way for future clinical trials and therapeutic interventions. This work represents a valuable resource in an underserved population, supporting pioneering research within GP2 and beyond. Deciphering causal and genetic risk factors in all these ancestries will help determine whether interventions, potential targets for disease modifying treatment, and prevention strategies that are being studied in the European populations are relevant to the African and African admixed populations.

Implications of all the Available Evidence

We nominate a novel signal impacting GBA1 as the major genetic risk factor for PD in the African and African admixed populations. The present study could inform future GBA1 clinical trials, improving patient stratification. In this regard, genetic testing can help to design trials likely to provide meaningful and actionable answers. It is our hope that these findings may ultimately have clinical utility for this underrepresented population.

A Comprehensive NMR Analysis of Serum and Fecal Metabolites in Familial Dysautonomia Patients Reveals Significant Metabolic Perturbations

Central metabolism has a profound impact on the clinical phenotypes and penetrance of neurological diseases such as Alzheimer’s (AD) and Parkinson’s (PD) diseases, Amyotrophic Lateral Sclerosis (ALS) and Autism Spectrum Disorder (ASD). In contrast to the multifactorial origin of these neurological diseases, neurodevelopmental impairment and neurodegeneration in Familial Dysautonomia (FD) results from a single point mutation in the ELP1 gene. FD patients represent a well-defined population who can help us better understand the cellular networks underlying neurodegeneration, and how disease traits are affected by metabolic dysfunction, which in turn may contribute to dysregulation of the gut–brain axis of FD. Here, 1H NMR spectroscopy was employed to characterize the serum and fecal metabolomes of FD patients, and to assess similarities and differences in the polar metabolite profiles between FD patients and healthy relative controls. Findings from this work revealed noteworthy metabolic alterations reflected in energy (ATP) production, mitochondrial function, amino acid and nucleotide catabolism, neurosignaling molecules, and gut-microbial metabolism. These results provide further evidence for a close interconnection between metabolism, neurodegeneration, and gut microbiome dysbiosis in FD, and create an opportunity to explore whether metabolic interventions targeting the gut–brain–metabolism axis of FD could be used to redress or slow down the progressive neurodegeneration observed in FD patients.

Gastrointestinal bleeding in children with familial dysautonomia: a case-control study

OBJECTIVE

Familial dysautonomia (FD) is a rare inherited autosomal recessive disorder with abnormal somatosensory, enteric, and afferent autonomic neurons. We aimed to define the incidence of gastrointestinal bleeding and its associated risk factors in patients with FD.

METHODS

In this retrospective case-control study, we identified all episodes of gastrointestinal bleeding in patients with FD, occurring over four decades (January 1980-December 2017), using the New York University FD registry.

RESULTS

We identified 104 episodes of gastrointestinal bleeding occurring in 60 patients with FD. The estimated incidence rate of gastrointestinal bleeds in the FD population rate was 4.20 episodes per 1000 person-years. We compared the 60 cases with 94 age-matched controls. Bleeding in the upper gastrointestinal tract from gastric and duodenal ulcers occurred most frequently (64 bleeds, 75.6%). Patients were more likely to have a gastrostomy (G)-tube and a Nissen fundoplication [odds ratio (OR) 3.73, 95% confidence interval (CI) 1.303-13.565] than controls. The mean time from G-tube placement to first gastrointestinal bleed was 7.01 years. The mean time from Nissen fundoplication to bleed was 7.01 years. Cases and controls had similar frequency of intake of nonsteroidal antiinflammatory drugs (NSAID) and selective serotonin reuptake inhibitors (SSRI).

CONCLUSION

The incidence of gastrointestinal bleeding in the pediatric FD population was estimated to be 4.20 per 1000 person-years, 21 times higher than in the general pediatric population (0.2 per 1000 person-years). Patients with FD with a G-tube and a Nissen fundoplication had a higher risk of a subsequent gastrointestinal bleeding.

Gut microbiome dysbiosis drives metabolic dysfunction in Familial dysautonomia

Familial dysautonomia (FD) is a rare genetic neurologic disorder caused by impaired neuronal development and progressive degeneration of both the peripheral and central nervous systems. FD is monogenic, with >99.4% of patients sharing an identical point mutation in the elongator acetyltransferase complex subunit 1 (ELP1) gene, providing a relatively simple genetic background in which to identify modifiable factors that influence pathology. Gastrointestinal symptoms and metabolic deficits are common among FD patients, which supports the hypothesis that the gut microbiome and metabolome are altered and dysfunctional compared to healthy individuals. Here we show significant differences in gut microbiome composition (16 S rRNA gene sequencing of stool samples) and NMR-based stool and serum metabolomes between a cohort of FD patients (~14% of patients worldwide) and their cohabitating, healthy relatives. We show that key observations in human subjects are recapitulated in a neuron-specific Elp1-deficient mouse model, and that cohousing mutant and littermate control mice ameliorates gut microbiome dysbiosis, improves deficits in gut transit, and reduces disease severity. Our results provide evidence that neurologic deficits in FD alter the structure and function of the gut microbiome, which shifts overall host metabolism to perpetuate further neurodegeneration.

Fear conditioning as a pathogenic mechanism in the postural tachycardia syndrome

Despite its increasing recognition and extensive research, there is no unifying hypothesis on the pathophysiology of the postural tachycardia syndrome. In this cross-sectional study, we examined the role of fear conditioning and its association with tachycardia and cerebral hypoperfusion upon standing in 28 patients with postural tachycardia syndrome (31 ± 12 years old, 25 women) and 21 matched controls. We found that patients had higher somatic vigilance (p = 0.0167) and more anxiety (p < 0.0001). They also had a more pronounced anticipatory tachycardia right before assuming the upright position in a tilt-table test (p = 0.015), a physiologic indicator of fear conditioning to orthostasis. While standing, patients had faster heart rate (p < 0.001), higher plasma catecholamine levels (p = 0.020), lower end-tidal CO2 (p = 0.005), and reduced middle cerebral artery blood flow velocity (p = 0.002). Multi-linear logistic regression modeling showed that both epinephrine secretion and excessive somatic vigilance predicted the magnitude of the tachycardia and the hyperventilation. These findings suggest that the postural tachycardia syndrome is a functional psychogenic disorder in which standing may acquire a frightful quality, so that even when experienced alone, it elicits a fearful conditioned response. Heightened somatic anxiety is associated with and may predispose to a fear-conditioned hyperadrenergic state when standing. Our results have therapeutic implications.

Stress and the baroreflex

The stress response to emotions elicits the release of glucocorticoids from the adrenal cortex, epinephrine from the adrenal medulla, and norepinephrine from the sympathetic nerves. The baroreflex adapts to buffer these responses to ensure that perfusion to the organs meets the demands while maintaining blood pressure within a within a narrow range. While stressor-evoked autonomic cardiovascular responses may be adaptive for the short-term, the recurrent exaggerated cardiovascular stress reactions can be maladaptive in the long-term. Prolonged stress or loss of the baroreflex's buffering capacity can predispose episodes of heightened sympathetic activity during stress leading to hypertension, tachycardia, and ventricular wall motion abnormalities. This review discusses 1) how the baroreflex responds to acute and chronic stressors, 2) how lesions in the neuronal pathways of the baroreflex alter the ability to respond or counteract the stress response, and 3) the techniques to assess baroreflex sensitivity and stress responses. Evidence suggests that loss of baroreflex sensitivity may predispose heightened autonomic responses to stress and at least in part explain the association between stress, mortality and cardiovascular diseases.

Safety and efficacy of ampreloxetine in symptomatic neurogenic orthostatic hypotension: a phase 2 trial

PURPOSE

In neurogenic orthostatic hypotension, blood pressure falls when upright owing to impaired release of norepinephrine, leading to dizziness. Ampreloxetine, a selective norepinephrine reuptake inhibitor, increases circulating norepinephrine levels. This study explored the safety of ampreloxetine and its effect on blood pressure and symptoms in patients with neurogenic orthostatic hypotension.

METHODS

A multicenter ascending-dose trial (range 1-20 mg, Part A) was followed by a 1 day, double-blind, randomized, placebo-controlled study (median dose 15 mg, Part B). Eligible patients then enrolled in a 20-week, open-label, steady-state extension phase (median dose 10 mg, Part C) followed by a 4-week withdrawal. Assessments included the Orthostatic Hypotension Symptom Assessment Scale (item 1), supine/seated/standing blood pressure, and safety.

RESULTS

Thirty-four patients (age 66 ± 8 years, 22 men) were enrolled. Part A: The proportion of participants with a positive response (i.e., increase from baseline in seated systolic blood pressure of ≥ 10 mmHg) was greater with the 5 and 10 mg ampreloxetine doses than with placebo or other active ampreloxetine doses. Part B: Seated blood pressure increased 15.7 mmHg 4 h after ampreloxetine and decreased 14.2 mmHg after placebo [least squares mean difference (95% CI) 29.9 mmHg (7.6-52.3); P = 0.0112]. Part C: Symptoms of dizziness/lightheadedness improved 3.1 ± 3.0 points from baseline and standing systolic blood pressure increased 11 ± 12 mmHg. After 4 weeks of withdrawal, symptoms returned to pretreatment levels. The effect of ampreloxetine on supine blood pressure was minimal throughout treatment duration.

CONCLUSION

Ampreloxetine was well tolerated and improved orthostatic symptoms and seated/standing blood pressure with little change in supine blood pressure.

TRIAL REGISTRATION

NCT02705755 (first posted March 10, 2016).

Pharmacokinetics and pharmacodynamics of ampreloxetine, a novel, selective norepinephrine reuptake inhibitor, in symptomatic neurogenic orthostatic hypotension

Purpose

Ampreloxetine is a novel, selective, long-acting norepinephrine reuptake (NET) inhibitor being investigated as a once-daily oral treatment for symptomatic neurogenic orthostatic hypotension (nOH) in patients with autonomic synucleinopathies. The purpose of this study was to characterize the pharmacokinetic and pharmacodynamic profiles of ampreloxetine in this target population.

Methods

Patients with nOH were enrolled in a multicenter, phase II clinical trial of ampreloxetine (NCT02705755). They received escalating doses over 5 days in the clinical research unit, followed by 20 weeks of open-label treatment and then a 4-week withdrawal. As neurochemical biomarkers of NET inhibition, we assayed plasma concentrations of norepinephrine (NE) and its main intraneuronal metabolite 3,4-dihydroxyphenylglycol (DHPG) pre- and post-ampreloxetine.

Results

Thirty-four patients with nOH were enrolled. Plasma ampreloxetine concentrations increased with repeated escalating doses, with peak concentrations observed 6–9 h post-drug administration. The median ampreloxetine dose in the 20-week treatment phase was 10 mg once daily. Plasma ampreloxetine concentrations reached steady state by 2 weeks, with stable plasma levels over 24 h. No influence of age or renal function on ampreloxetine plasma concentrations was observed. On treatment, compared to baseline, plasma NE significantly increased by 71% (p < 0.005), plasma DHPG significantly declined by 22% (p < 0.05), and the NE:DHPG ratio significantly increased (p < 0.001).

Conclusions

Persistent elevation of plasma NE levels accompanied by reduced DHPG levels after ampreloxetine suggests reduced neuronal reuptake and metabolism of NE in postganglionic efferent sympathetic neurons. The findings are consistent with long-lasting NET inhibition, which may increase vasoconstrictor tone, supporting once-daily ampreloxetine dosing in patients with nOH.

Expanding the Genotypic Spectrum of Congenital Sensory and Autonomic Neuropathies Using Whole-Exome Sequencing

Objective

To test the hypothesis that many patients presenting with congenital insensitivity to pain have lesser known or unidentified mutations not captured by conventional genetic panels, we performed whole-exome sequencing in a cohort of well-characterized patients with a clinical diagnosis of congenital hereditary sensory and autonomic neuropathy with unrevealing conventional genetic testing.

Methods

We performed whole-exome sequencing (WES) in 13 patients with congenital impaired or absent sensation to pain and temperature with no identified molecular diagnosis from a conventional genetic panel. Patients underwent a comprehensive phenotypic assessment including autonomic function testing, and neurologic and ophthalmologic examinations.

Results

We identified known or likely pathogenic genetic causes of congenital insensitivity to pain in all 13 patients, spanning 9 genes, the vast majority of which were inherited in an autosomal recessive manner. These included known pathogenic variants (3 patients harboring mutations in TECPR2 and SCN11A), suspected pathogenic variants in genes described to cause congenital sensory and autonomic syndromes (7 patients harboring variants in NGF, LIFR, SCN9A, and PRDM12), and likely pathogenic variants in novel genes (4 patients harboring variants in SMPDL3A, PLEKHN1, and SCN10A).

Conclusions

Our results expand the genetic landscape of congenital sensory and autonomic neuropathies. Further validation of some identified variants should confirm their pathogenicity. WES should be clinically considered to expedite diagnosis, reduce laboratory investigations, and guide enrollment in future gene therapy trials.

Von Economo Neuron Pathology in Familial Dysautonomia: Quantitative Assessment and Possible Implications

Von Economo neurons (VENs) and fork cells are principally located in the anterior cingulate cortex (ACC) and the frontoinsular cortex (FI). Both of these regions integrate inputs from the autonomic nervous system (ANS) and are involved in decision-making and perception of the emotional states of self and others. Familial dysautonomia (FD) is an orphan disorder characterized by autonomic dysfunction and behavioral abnormalities including repetitive behavior and emotional rigidity, which are also seen in autism spectrum disorder. To understand a possible link between the ANS and the cortical regions implicated in emotion regulation we studied VENs and fork cells in an autonomic disorder. We determined the densities of VENs, fork cells, and pyramidal neurons and the ratio of VENs and fork cells to pyramidal neurons in ACC and FI in 4 FD patient and 6 matched control brains using a stereologic approach. We identified alterations in densities of VENs and pyramidal neurons and their distributions in the ACC and FI in FD brains. These data suggest that alterations in migration and numbers of VENs may be involved in FD pathophysiology thereby supporting the notion of a functional link between VENs, the ANS and the peripheral nervous system in general.

Genome sequencing analysis identifies new loci associated with Lewy body dementia and provides insights into its genetic architecture

The genetic basis of Lewy body dementia (LBD) is not well understood. Here, we performed whole-genome sequencing in large cohorts of LBD cases and neurologically healthy controls to study the genetic architecture of this understudied form of dementia, and to generate a resource for the scientific community. Genome-wide association analysis identified five independent risk loci, whereas genome-wide gene-aggregation tests implicated mutations in the gene GBA. Genetic risk scores demonstrate that LBD shares risk profiles and pathways with Alzheimer's disease and Parkinson's disease, providing a deeper molecular understanding of the complex genetic architecture of this age-related neurodegenerative condition.

Limitations of the Unified Multiple System Atrophy Rating Scale as outcome measure for clinical trials and a roadmap for improvement

PURPOSE

The unified multiple system atrophy (MSA) rating scale (UMSARS) was developed almost 20 years ago as a clinical rating scale to capture multiple aspects of the disease. With its widespread use, the shortcomings of the UMSARS as a clinical outcome assessment (COA) have become increasingly apparent. We here summarize the shortcomings of the scale, confirm some of its limitations with data from the Natural History Study of the Synucleinopathies (NHSS), and suggest a framework to develop and validate an improved COA to be used in future clinical trials of disease-modifying drugs in patients with MSA.

METHODS

Expert consensus assessment of the limitations of the UMSARS and recommendations for the development and validation of a novel COA for MSA. We used UMSARS data from the ongoing NHSS (ClinicalTrials.gov: NCT01799915) to showcase some of these limitations.

RESULTS

The UMSARS in general, and specific items in particular, have limitations to detect change resulting in a ceiling effect. Some items have specific limitations including unclear anchoring descriptions, lack of correlation with disease severity, susceptibility to improve with symptomatic therapies (e.g., orthostatic hypotension, constipation, and bladder dysfunction), and redundancy, among others.

CONCLUSIONS

Because of the limitations of the UMSARS, developing and validating an improved COA is a priority. The time is right for academic MSA clinicians together with industry, professional societies, and patient advocacy groups to develop and validate a new COA.

Human papillomavirus (HPV) vaccine and autonomic disorders: a position statement from the American Autonomic Society

INTRODUCTION

Human papillomavirus (HPV) vaccination has been anecdotally connected to development of dysautonomia, chronic fatigue, complex regional pain syndrome and postural tachycardia syndrome.

OBJECTIVES

To critically evaluate a potential connection between HPV vaccination and above noted conditions.

METHODS

We reviewed the literature containing the biology of the virus, pathophysiology of infection, epidemiology of associated cancers, indications of HPV vaccination, safety surveillance data and published reports linking HPV vaccination to autonomic disorders.

RESULTS

At this time the American Autonomic Society finds that there are no data to support a causal relationship between HPV vaccination and CRPS, chronic fatigue, POTS or other forms of dysautonomia.

CONCLUSIONS

Certain conditions are prevalent in the same patient populations that are vaccinated with the HPV vaccine (peri-pubertal males and females). This association, however, is insufficient proof of causality.

Autoantibodies Blocking M3 Muscarinic Receptors Cause Postganglionic Cholinergic Dysautonomia

A 10-year-old girl presented with ileus, urinary retention, dry mouth, lack of tears, fixed dilated pupils, and diffuse anhidrosis 7 days after a febrile illness. We hypothesized that her syndrome was due to autoimmunity against muscarinic acetylcholine receptors, blocking their activation. Using an indirect enzyme-linked immunosorbent assay for all 5 muscarinic receptors (M₁ -M₅ ), we identified in the patient's serum antibodies that selectively bound to M₃ receptors. In vitro functional studies confirmed that these autoantibodies selectively blocked M₃ receptor activation. Thus, autoantibodies against M₃ acetylcholine receptors cause acute postganglionic cholinergic dysautonomia. ANN NEUROL 2020;88:1237-1243.

Afferent Baroreflex Dysfunction: Decreased or Excessive Signaling Results in Distinct Phenotypes

Head and neck tumors can affect afferent baroreceptor neurons and either interrupt or intermittently increase their signaling, causing blood pressure to become erratic. When the afferent fibers of the baroreflex are injured by surgery or radiotherapy or fail to develop as in familial dysautonomia, their sensory information is no longer present to regulate arterial blood pressure, resulting in afferent baroreflex failure. When the baroreflex afferents are abnormally activated, such as by paragangliomas in the neck, presumably by direct compression, they trigger acute hypotension and bradycardia and frequently syncope, by a mechanism similar to the carotid sinus syndrome. We describe our observations in a large series of 23 patients with afferent baroreflex dysfunction and the cardiovascular autonomic features that arise when the sensory baroreceptor neurons are injured or compressed. The management of afferent baroreceptor dysfunction is limited, but pharmacological strategies can mitigate blood pressure swings, improve symptoms, and may reduce hypertensive organ damage. Although rare, the prevalence of afferent baroreflex dysfunction appears to be increasing in middle-aged men due to human papillomavirus related oropharyngeal cancer.

Carbidopa for Afferent Baroreflex Failure in Familial Dysautonomia: A Double-Blind Randomized Crossover Clinical Trial

Afferent lesions of the arterial baroreflex occur in familial dysautonomia. This leads to excessive blood pressure variability with falls and frequent surges that damage the organs. These hypertensive surges are the result of excess peripheral catecholamine release and have no adequate treatment. Carbidopa is a selective DOPA-decarboxylase inhibitor that suppresses catecholamines production outside the brain. To learn whether carbidopa can inhibit catecholamine-induced hypertensive surges in patients with severe afferent baroreflex failure, we conducted a double-blind randomized crossover trial in which patients with familial dysautonomia received high dose carbidopa (600 mg/day), low-dose carbidopa (300 mg/day), or matching placebo in 3 4-week treatment periods. Among the 22 patients enrolled (13 females/8 males), the median age was 26 (range, 12-59 years). At enrollment, patients had hypertensive peaks to 164/116 (range, 144/92 to 213/150 mm Hg). Twenty-four hour urinary norepinephrine excretion, a marker of peripheral catecholamine release, was significantly suppressed on both high dose and low dose carbidopa, compared with placebo (P=0.0075). The 2 co-primary end points of the trial were met. The SD of systolic BP variability was reduced at both carbidopa doses (low dose: 17±4; high dose: 18±5 mm Hg) compared with placebo (23±7 mm Hg; P=0.0013), and there was a significant reduction in the systolic BP peaks on active treatment (P=0.0015). High- and low-dose carbidopa were similarly effective and well tolerated. This study provides class Ib evidence that carbidopa can reduce blood pressure variability in patients with congenital afferent baroreflex failure. Similar beneficial effects are observed in patients with acquired baroreflex lesions.

Autonomic function testing in the COVID-19 pandemic: an American Autonomic Society position statement

COVID-19 is a global pandemic that is wreaking havoc with the health and economy of much of human civilization. In this document from the American Autonomic Society, we identify the potential risks of exposure to patients, physicians, and allied healthcare staff. We provide guidance for conducting autonomic function testing safely in this environment.

Elbow proprioception is normal in patients with a congenital absence of functional muscle spindles

KEY POINTS

Individuals with hereditary sensory and autonomic neuropathy type III (HSAN III), also known as Riley-Day syndrome or familial dysautonomia, do not have functional muscle spindle afferents but do have essentially normal cutaneous mechanoreceptors. Lack of muscle spindle feedback from the legs may account for the poor proprioception at the knee and the ataxic gait typical of HSAN III. Given that functional muscle spindle afferents are also absent in the upper limb, we assessed whether proprioception at the elbow was likewise compromised. Passive joint angle matching showed that proprioception was normal at the elbow, suggesting that individuals with HSAN III rely more on cutaneous afferents around the elbow.

ABSTRACT

Hereditary sensory and autonomic neuropathy type III (HSAN III) is a rare neurological condition that features a marked ataxic gait that progressively worsens over time. We have shown that functional muscle spindle afferents are absent in the upper and lower limbs in HSAN III, and we have argued that this may account for the ataxia. We recently used passive joint angle matching to demonstrate that proprioception of the knee joint is very poor in HSAN III but can be improved towards normal by application of elastic kinesiology tape across the knee joints, which we attribute to the presence of intact cutaneous mechanoreceptors. Here we assessed whether proprioception was equally compromised at the elbow joint, and whether it could be improved through taping. Proprioception at the elbow joint was assessed using passive joint angle matching in 12 HSAN III patients and 12 age-matched controls. There was no difference in absolute error, gradient or correlation coefficient of the relationship between joint angles of the reference and indicator arms. Unlike at the knee, taping did not improve elbow proprioception in either group. Clearly, the lack of muscle spindles compromised proprioception at the knee but not at the elbow, and we suggest that the HSAN III patients rely more on proprioceptive signals from the skin around the elbow.

Impact of depressive symptoms on self-perceived severity of autonomic dysfunction in multiple system atrophy: relevance for patient-reported outcomes in clinical trials

PURPOSE

To assess the relationship between depressive symptoms and self-perceived severity of autonomic dysfunction in patients with multiple system atrophy (MSA).

METHODS

Cross-sectional evaluation of patients with MSA who underwent autonomic testing, Unified MSA Rating Scale (UMSARS)-1 and -2, rating of the presence and severity of depressive symptoms (Zung scale), quality of life (SF-36), body vigilance, anxiety (Spielberger's anxiety scale), severity of autonomic dysfunction with the Composite Autonomic Symptoms Score (COMPASS-31), and severity of orthostatic hypotension (OH) symptoms with the Orthostatic Hypotension Questionnaire (OHQ).

RESULTS

Fifty-eight patients (32 women) with probable MSA (aged 61.8 ± 8.6 years; disease duration 4.3 ± 2.1 years) were studied. Forty patients (69%) had symptoms of depression in the Zung scale. Age, disease duration, and motor disability were similar in those with and without symptoms of depression. Despite a similar orthostatic blood pressure fall, the severity of orthostatic symptoms was higher in patients with symptoms of depression (p = 0.004). Depression scores were associated with higher burden of autonomic symptoms (R = 0.401, p = 0.02), specifically with the COMPASS-31 items related to orthostatic intolerance (R = 0.337, p = 0.045), and with the OHQ (R = 0.529; p < 0.001). A multivariable regression model including age, sex, UMSARS, and drop in systolic blood pressure upon head-up tilt as covariates showed that the burden of depressive symptoms was independently associated with the OHQ score: for every 1-unit increase in the Zung depression score, there was a 1.181-point increase in the total OHQ score.

CONCLUSIONS

In patients with MSA, depressive symptoms worsen the perceived severity of autonomic symptoms in general and orthostatic hypotension in particular. Our findings have implications for clinical trial design.

Quantitative magnetic resonance evaluation of the trigeminal nerve in familial dysautonomia

PURPOSE

Familial dysautonomia (FD) is a rare autosomal recessive disease that affects the development of sensory and autonomic neurons, including those in the cranial nerves. We aimed to determine whether conventional brain magnetic resonance imaging (MRI) could detect morphologic changes in the trigeminal nerves of these patients.

METHODS

Cross-sectional analysis of brain MRI of patients with genetically confirmed FD and age- and sex-matched controls. High-resolution 3D gradient-echo T1-weighted sequences were used to obtain measurements of the cisternal segment of the trigeminal nerves. Measurements were obtained using a two-reader consensus.

RESULTS

Twenty pairs of trigeminal nerves were assessed in ten patients with FD and ten matched controls. The median (interquartile range) cross-sectional area of the trigeminal nerves in patients with FD was 3.5 (2.1) mm², compared to 5.9 (2.0) mm² in controls (P < 0.001). No association between trigeminal nerve area and age was found in patients or controls.

CONCLUSIONS

Using conventional MRI, the caliber of the trigeminal nerves was significantly reduced bilaterally in patients with FD compared to controls, a finding that appears to be highly characteristic of this disorder. The lack of correlation between age and trigeminal nerve size supports arrested neuronal development rather than progressive atrophy.

Chemoreflex failure and sleep-disordered breathing in familial dysautonomia: Implications for sudden death during sleep

Familial dysautonomia (Riley-Day syndrome, hereditary sensory and autonomic neuropathy type III) is a rare autosomal recessive disease characterized by impaired development of primary sensory and autonomic neurons resulting in a severe neurological phenotype, which includes arterial baroreflex and chemoreflex failure with high frequency of sleep-disordered breathing and sudden death during sleep. Although a rare disease, familial dysautonomia represents a unique template to study the interactions between sleep-disordered breathing and abnormal chemo- and baroreflex function. In patients with familial dysautonomia, ventilatory responses to hypercapnia are reduced, and to hypoxia are almost absent. In response to hypoxia, these patients develop paradoxical hypoventilation, hypotension, bradycardia, and potentially, death. Impaired ventilatory control due to chemoreflex failure acquires special relevance during sleep when conscious control of respiration withdraws. Overall, almost all adult (85%) and pediatric (95%) patients have some degree of sleep-disordered breathing. Obstructive apnea events are more frequent in adults, whereas central apnea events are more severe and frequent in children. The annual incidence rate of sudden death during sleep in patients with familial dysautonomia is 3.4 per 1000 person-year, compared to 0.5-1 per 1000 person-year of sudden unexpected death in epilepsy. This review summarizes recent developments in the understanding of sleep-disordered breathing in patients with familial dysautonomia, the risk factors for sudden death during sleep, and the specific interventions that could prevent it.

Supine plasma NE predicts the pressor response to droxidopa in neurogenic orthostatic hypotension

OBJECTIVE

To test whether the plasma levels of norepinephrine (NE) in patients with neurogenic orthostatic hypotension (nOH) predict their pressor response to droxidopa.

METHODS

This was an observational study, which included patients with nOH. All patients had standardized autonomic function testing including determination of venous plasma catecholamine levels drawn through an indwelling catheter while resting supine. This was followed by a droxidopa titration with 100 mg increments in successive days until relief of symptoms, side effects, or the maximum dose of 600 mg was reached. No response was defined as an increase of <10 mm Hg in systolic blood pressure (BP) after 3-minute standing 1 hour after droxidopa administration. Nonlinear regression models were used to determine the relationship between BP response and plasma NE levels.

RESULTS

We studied 20 patients with nOH due to Parkinson disease, pure autonomic failure, multiple system atrophy, or autoimmune autonomic neuropathies. Their supine plasma NE levels ranged from 44 to 850 pg/mL. Lower supine plasma NE levels were associated with greater pressor effect 1 hour after dose (R² = 0.49) and higher standing BP (R² = 0.45). Patients with no pressor response to droxidopa had higher NE levels (382 ± 100 vs 115 ± 20 pg/mL, p = 0.0014). A supine NE level of <219.5 pg/mL had 83% sensitivity and 93% specificity to predict a pressor response (area under the curve = 0.95, p = 0.0023).

CONCLUSIONS

In patients with nOH, lower supine resting plasma NE levels are associated with a greater pressor effect of droxidopa treatment. This finding should help identify patients with nOH most likely to respond to standard doses of droxidopa.

CLASSIFICATION OF EVIDENCE

This study provides Class I evidence that lower supine plasma NE levels accurately identify patients with nOH more likely to have a greater pressor effect from droxidopa.

Impaired sensorimotor control of the hand in congenital absence of functional muscle spindles

Patients with hereditary sensory and autonomic neuropathy type III (HSAN III) exhibit marked ataxia, including gait disturbances. We recently showed that functional muscle spindle afferents in the leg, recorded via intraneural microelectrodes inserted into the peroneal nerve, are absent in HSAN III, although large-diameter cutaneous afferents are intact. Moreover, there is a tight correlation between loss of proprioceptive acuity at the knee and the severity of gait impairment. We tested the hypothesis that manual motor performance is also compromised in HSAN III, attributed to the predicted absence of muscle spindles in the intrinsic muscles of the hand. Manual performance in the Purdue pegboard task was assessed in 12 individuals with HSAN III and 11 age-matched healthy controls. The mean (±SD) pegboard score (number of pins inserted in 30 s) was 8.1 ± 1.9 and 8.6 ± 1.8 for the left and right hand, respectively, significantly lower than the scores for the controls (15.0 ± 1.3 and 16.0 ± 1.1; P < 0.0001). Performance was not improved after kinesiology tape was applied over the joints of the hand. In 5 patients we inserted a tungsten microelectrode into the ulnar nerve at the wrist. No spontaneous or stretch-evoked muscle afferent activity could be identified in any of the 11 fascicles supplying intrinsic muscles of the hand, whereas touch-evoked activity from low-threshold cutaneous mechanoreceptor afferents could readily be recorded from 4 cutaneous fascicles. We conclude that functional muscle spindles are absent in the short muscles of the hand and most likely absent in the long finger flexors and extensors, and that this largely accounts for the poor manual motor performance in HSAN III. NEW & NOTEWORTHY We describe the impaired manual motor performance in patients with hereditary sensory and autonomic neuropathy type III (Riley-Day syndrome), who exhibit congenital insensitivity to pain, poor proprioception, and marked gait ataxia. We show that functional muscle spindles are absent in the intrinsic muscles of the hand, which we argue contributes to their poor performance in a task involving the precision grip.

Respiratory care in familial dysautonomia: Systematic review and expert consensus recommendations

BACKGROUND

Familial dysautonomia (Riley-Day syndrome, hereditary sensory autonomic neuropathy type-III) is a rare genetic disease caused by impaired development of sensory and afferent autonomic nerves. As a consequence, patients develop neurogenic dysphagia with frequent aspiration, chronic lung disease, and chemoreflex failure leading to severe sleep disordered breathing. The purpose of these guidelines is to provide recommendations for the diagnosis and treatment of respiratory disorders in familial dysautonomia.

METHODS

We performed a systematic review to summarize the evidence related to our questions. When evidence was not sufficient, we used data from the New York University Familial Dysautonomia Patient Registry, a database containing ongoing prospective comprehensive clinical data from 670 cases. The evidence was summarized and discussed by a multidisciplinary panel of experts. Evidence-based and expert recommendations were then formulated, written, and graded using the Grading of Recommendations, Assessment, Development, and Evaluation (GRADE) system.

RESULTS

Recommendations were formulated for or against specific diagnostic tests and clinical interventions. Diagnostic tests reviewed included radiological evaluation, dysphagia evaluation, gastroesophageal evaluation, bronchoscopy and bronchoalveolar lavage, pulmonary function tests, laryngoscopy and polysomnography. Clinical interventions and therapies reviewed included prevention and management of aspiration, airway mucus clearance and chest physical therapy, viral respiratory infections, precautions during high altitude or air-flight travel, non-invasive ventilation during sleep, antibiotic therapy, steroid therapy, oxygen therapy, gastrostomy tube placement, Nissen fundoplication surgery, scoliosis surgery, tracheostomy and lung lobectomy.

CONCLUSIONS

Expert recommendations for the diagnosis and management of respiratory disease in patients with familial dysautonomia are provided. Frequent reassessment and updating will be needed.

Prevalence and characteristics of sleep-disordered breathing in familial dysautonomia

OBJECTIVE

Familial dysautonomia (FD) is an autosomal recessive disorder characterized by impaired development of sensory and afferent autonomic nerves. Untreated sleep-disordered breathing (SDB) has been reported to increase the risk of sudden unexpected death in FD. We aimed to describe the prevalence and characteristics of SDB in FD.

PATIENTS/METHODS

Seventy-five patients with FD (20 adults and 55 children) underwent in-lab polysomnography, including peripheral capillary oxygen saturation (SpO2) and end-tidal capnography (EtCO2) measurements. A t-test and Spearman's correlation analysis were performed to evaluate the impact of age on sleep, occurrence of apneas, SpO2 and EtCO2 levels; and to determine the relationship between apneas and SpO2/EtCO2 measurements during different sleep stages.

RESULTS

Overall, 85% of adults and 91% of pediatric patients had some degree of SDB. Obstructive sleep apneas were more severe in adults (8.5 events/h in adults vs. 3.5 events/h in children, p = 0.04), whereas central apneas were more severe (10.8 vs. 2.8 events/h, p = 0.04) and frequent (61.8% vs. 45%, p = 0.017) in children. Overall, a higher apnea-hypopnea index was associated with increased severity of hypoxia and hypoventilation, although in a significant fraction of patients (67% and 46%), hypoxemia and hypoventilation occurred independent of apneas.

CONCLUSION

Most adult and pediatric patients with FD suffer from some degree of SDB. There was a differential effect of age in the pattern of SDB observed. In some FD patients, hypoventilation and hypoxia occurred independently of apneas. Therefore, we recommend including EtCO2 monitoring during polysomnography in all patients with FD to detect SDB.

Diagnosis of multiple system atrophy

Multiple system atrophy (MSA) may be difficult to distinguish clinically from other disorders, particularly in the early stages of the disease. An autonomic-only presentation can be indistinguishable from pure autonomic failure. Patients presenting with parkinsonism may be misdiagnosed as having Parkinson disease. Patients presenting with the cerebellar phenotype of MSA can mimic other adult-onset ataxias due to alcohol, chemotherapeutic agents, lead, lithium, and toluene, or vitamin E deficiency, as well as paraneoplastic, autoimmune, or genetic ataxias. A careful medical history and meticulous neurological examination remain the cornerstone for the accurate diagnosis of MSA. Ancillary investigations are helpful to support the diagnosis, rule out potential mimics, and define therapeutic strategies. This review summarizes diagnostic investigations useful in the differential diagnosis of patients with suspected MSA. Currently used techniques include structural and functional brain imaging, cardiac sympathetic imaging, cardiovascular autonomic testing, olfactory testing, sleep study, urological evaluation, and dysphagia and cognitive assessments. Despite advances in the diagnostic tools for MSA in recent years and the availability of consensus criteria for clinical diagnosis, the diagnostic accuracy of MSA remains sub-optimal. As other diagnostic tools emerge, including skin biopsy, retinal biomarkers, blood and cerebrospinal fluid biomarkers, and advanced genetic testing, a more accurate and earlier recognition of MSA should be possible, even in the prodromal stages. This has important implications as misdiagnosis can result in inappropriate treatment, patient and family distress, and erroneous eligibility for clinical trials of disease-modifying drugs.

Orthostatic heart rate changes in patients with autonomic failure caused by neurodegenerative synucleinopathies

OBJECTIVE

Blunted tachycardia during hypotension is a characteristic feature of patients with autonomic failure, but the range has not been defined. This study reports the range of orthostatic heart rate (HR) changes in patients with autonomic failure caused by neurodegenerative synucleinopathies.

METHODS

Patients evaluated at sites of the U.S. Autonomic Consortium (NCT01799915) underwent standardized autonomic function tests and full neurological evaluation.

RESULTS

We identified 402 patients with orthostatic hypotension (OH) who had normal sinus rhythm. Of these, 378 had impaired sympathetic activation (ie, neurogenic OH) and based on their neurological examination were diagnosed with Parkinson disease, dementia with Lewy bodies, pure autonomic failure, or multiple system atrophy. The remaining 24 patients had preserved sympathetic activation and their OH was classified as nonneurogenic, due to volume depletion, anemia, or polypharmacy. Patients with neurogenic OH had twice the fall in systolic blood pressure (SBP; -44 ± 25 vs -21 ± 14 mmHg [mean ± standard deviation], p < 0.0001) but only one-third of the increase in HR of those with nonneurogenic OH (8 ± 8 vs 25 ± 11 beats per minute [bpm], p < 0.0001). A ΔHR/ΔSBP ratio of 0.492 bpm/mmHg had excellent sensitivity (91.3%) and specificity (88.4%) to distinguish between patients with neurogenic from nonneurogenic OH (area under the curve = 0.96, p < 0.0001). Within patients with neurogenic OH, HR increased more in those with multiple system atrophy (p = 0.0003), but there was considerable overlap with patients with Lewy body disorders.

INTERPRETATION

A blunted HR increase during hypotension suggests a neurogenic cause. A ΔHR/ΔSBP ratio < 0.5 bpm/mmHg is diagnostic of neurogenic OH. Ann Neurol 2018;83:522-531.

Founder mutation in IKBKAP gene causes vestibular impairment in familial dysautonomia

OBJECTIVE

To assess vestibular function in patients with familial dysautonomia (FD), a hereditary sensory and autonomic neuropathy - caused by a mutation in the IKBKAP gene (c.2204 + 6 T>C) - and characterized by marked gait ataxia.

METHODS

Cervical and vestibular evoked myogenic potentials (cVEMPs and oVEMPs) were recorded from the sternocleidomastoid (SCM) and extraocular muscles in 14 homozygous patients, 2 heterozygous patients, and 15 healthy controls during percussion of the forehead.

RESULTS

cVEMP and oVEMP amplitudes were significantly lower, and peak latencies significantly delayed, in the FD patients. There were no differences in overall EMG during attempted maximal voluntary contractions of the SCM muscle, suggesting intact efferent function. The two heterozygotes with a minor haplotype missense (R696P) mutation in exon 19 of the IKBKAP gene had cVEMP responses less affected than the homozygous.

CONCLUSIONS

The founder mutation in the IKBKAP gene affects the development of vestibular afferent pathways, leading to attenuated cVEMPs.

SIGNIFICANCE

Vestibular abnormalities may contribute to the gait ataxia in FD.

Sudden Unexpected Death During Sleep in Familial Dysautonomia: A Case-Control Study

Study Objectives

Sudden unexpected death during sleep (SUDS) is the most common cause of death in patients with familial dysautonomia (FD), an autosomal recessive disease characterized by sensory and autonomic dysfunction. It remains unknown what causes SUDS in these patients and who is at highest risk. We tested the hypothesis that SUDS in FD is linked to sleep-disordered breathing.

Methods

We retrospectively identified patients with FD who died suddenly and unexpectedly during sleep and had undergone polysomnography within the 18-month period before death. For each case, we sampled one age-matched surviving subject with FD that had also undergone polysomnography within the 18-month period before study. Data on polysomnography, EKG, ambulatory blood pressure monitoring, arterial blood gases, blood count, and metabolic panel were analyzed.

Results

Thirty-two deceased cases and 31 surviving controls were included. Autopsy was available in six cases. Compared with controls, participants with SUDS were more likely to be receiving treatment with fludrocortisone (odds ratio [OR]; 95% confidence interval) (OR 29.7; 4.1-213.4), have untreated obstructive sleep apnea (OR 17.4; 1.5-193), and plasma potassium levels <4 mEq/L (OR 19.5; 2.36-161) but less likely to use noninvasive ventilation at night (OR 0.19; 0.06-0.61).

Conclusions

Initiation of noninvasive ventilation when required and discontinuation of fludrocortisone treatment may reduce the high incidence rate of SUDS in patients with FD. Our findings contribute to the understanding of the link between autonomic, cardiovascular, and respiratory risk factors in SUDS.

Cerebral autoregulation and symptoms of orthostatic hypotension in familial dysautonomia

Familial dysautonomia is an inherited autonomic disorder with afferent baroreflex failure. We questioned why despite low blood pressure standing, surprisingly few familial dysautonomia patients complain of symptomatic hypotension or have syncope. Using transcranial Doppler ultrasonography of the middle cerebral artery, we measured flow velocity (mean, peak systolic, and diastolic), area under the curve, pulsatility index, and height of the dictrotic notch in 25 patients with familial dysautonomia and 15 controls. In patients, changing from sitting to a standing position, decreased BP from 124 ± 4/64 ± 3 to 82 ± 3/37 ± 2 mmHg (p < 0.0001, for both). Despite low BP, all patients denied orthostatic symptoms. Middle cerebral artery velocity fell minimally, and the magnitude of the reductions were similar to those observed in healthy controls, in whom BP upright did not fall. While standing, patients had a greater fall in cerebrovascular resistance (p < 0.0001), an increase in pulsatility (p < 0.0001), and a deepening of the dicrotic notch (p = 0.0010), findings all consistent with low cerebrovascular resistance. No significant changes occurred in controls. Patients born with baroreflex deafferentation retain the ability to buffer wide fluctuations in BP and auto-regulate cerebral blood flow. This explains how they can tolerate extremely low BPs standing that would otherwise induce syncope.

Natural history of pure autonomic failure: A United States prospective cohort

OBJECTIVE

To define the clinical features and biomarkers that predict which patients with pure autonomic failure will develop Parkinson disease, dementia with Lewy bodies, or multiple system atrophy.

METHODS

One hundred patients who presented with pure autonomic failure were recruited at 5 medical centers in the United States. Seventy-four patients agreed to be followed prospectively. Patients underwent clinical evaluations including neurological rating scales, sleep questionnaires, smell test, and sympathetic and parasympathetic cardiovascular autonomic function tests.

RESULTS

At enrollment, patients were 68 ± 12 years old (median ± interquartile range) and had had autonomic failure for 5 ± 7 years. Within 4 years of follow-up, 25 of 74 subjects (34%) developed dementia with Lewy bodies (n = 13), Parkinson disease (n = 6), or multiple system atrophy (n = 6). The presence of probable rapid eye movement (REM) sleep behavior disorder was strongly associated with the development of a manifest central nervous system (CNS) synucleinopathy (odds ratio = 7.1). Patients who phenoconverted to multiple system atrophy had younger age at onset of autonomic failure, severe bladder/bowel dysfunction, preserved olfaction, and a cardiac chronotropic response upon tilt > 10 beats per minute. Those who phenoconverted to Parkinson disease or dementia with Lewy bodies had decreased olfaction, a lesser chronotropic response to tilt, and a longer duration of illness. The small group of patients retaining the pure autonomic failure phenotype had very low plasma norepinephrine levels, slow resting heart rate, no REM sleep behavior disorder, and preserved smell.

INTERPRETATION

Patients presenting with pure autonomic failure are at high risk of phenoconverting to a manifest CNS synucleinopathy. Specific clinical features predict future diagnosis. Ann Neurol 2017;81:287-297.