Faculty Bibliography

STUDY OBJECTIVES: In familial dysautonomia (FD) patients, sleep-disordered breathing (SDB) might contribute to their high risk of sleep-related sudden death. Prevalence of central versus obstructive sleep apneas is controversial but may be therapeutically relevant. We, therefore, assessed sleep structure and SDB in FD-patients with no history of SDB. METHODS: 11 mildly affected FD-patients (28 +/- 11 years) without clinically overt SDB and 13 controls (28 +/- 10 years) underwent polysomnographic recording during one night. We assessed sleep stages, obstructive and central apneas (>/= 90% air flow reduction) and hypopneas (> 30% decrease in airflow with >/= 4% oxygen-desaturation), and determined obstructive (oAI) and central (cAI) apnea indices and the hypopnea index (HI) as count of respective apneas/hypopneas divided by sleep time. We obtained the apnea-hypopnea index (AHI4%) from the total of apneas and hypopneas divided by sleep time. We determined differences between FD-patients and controls using the U-test and within-group differences between oAIs, cAIs, and HIs using the Friedman test and Wilcoxon test. RESULTS: Sleep structure was similar in FD-patients and controls. AHI4% and HI were significantly higher in patients than controls. In patients, HIs were higher than oAIs and oAIs were higher than cAIs. In controls, there was no difference between HIs, oAIs, and cAIs. Only patients had apneas and hypopneas during slow wave sleep. CONCLUSIONS: In our FD-patients, obstructive apneas were more common than central apneas. These findings may be related to FD-specific pathophysiology. The potential ramifications of SDB in FD-patients suggest the utility of polysomnography to unveil SDB and initiate treatment. COMMENTARY: A commentary on this article appears in this issue on page 1583.

Familial dysautonomia (FD) features a unique combination of cardiovascular disturbances not seen in patients with any other chronic disorder of the autonomic nervous system. While blood pressure falls and both heart rate and plasma noradrenaline fail to increase during standing in FD, patients demonstrate significant increases in blood pressure and plasma noradrenaline during episodes of emotional arousal. This indicates that vasoconstrictor neurones can be activated during states of emotional arousal, and that noradrenaline is released. Because constriction of arterioles in skeletal muscle vascular beds is one of the primary determinants of total peripheral resistance and hence of blood pressure, we would expect that muscle sympathetic nerve activity (MSNA) -which is vasoconstrictor in function - would be present in patients with FD. However, given the absence of functional baroreflex afferents we predicted that MSNA would not appear as cardiac-locked bursts. We tested this hypothesis using tungsten microelectrodes inserted percutaneously into muscle or cutaneous fascicles of the nerve in 12 patients with FD. Spontaneous bursts of MSNA were absent in all patients, but in five patients we found evidence of tonically firing sympathetic neurones, with no cardiac rhythmicity, that increased their spontaneous discharge during emotional arousal but not during baroreceptor unloading. Conversely, skin sympathetic nerve activity (SSNA) appeared normal. We conclude that the loss of baroreflex modulation of MSNA contributes to the poor control of blood pressure in FD, and that the increase in tonic firing of muscle vasoconstrictor neurones contributes to the increase in blood pressure during emotional excitement

Introduction: Familial dysautonomia (FD)-patients are at risk of sudden unexplained death, particularly during sleep. Respiratory abnormalities and reduced arousability might contribute to fatalities. Aim: To assess respiratory abnormalities and arousability in FD during sleep. Methods: 11 FD-patients (28 +/- 11 years) and 11 healthy persons (28 +/- 11 years) underwent polysomnographic recording during one night. We assessed sleep stages, apneas (>90% air flow reduction) and hypopneas (>30% decrease in airflow with >4% oxygen-desaturation). Arousals were defined as >3 sec abrupt shift in electroencephalographic frequencies to alpha- or theta-activity or frequencies >16Hz. We tested differences between FD-patients and controls by U-test or Fisher's exact test (significance: p < 0.05). Results: Percentage of sleep stages was similar in FD-patients and controls. 107 apneas occurred in 10 FD-patients. Apneas were followed by 74 oxygen-desaturations and 4 arousals. 9 Apneas were followed by desaturation and arousal. Only 5 apneas (p < 0.001) occurred in 2 controls (p > 0.05) and were followed by 2 oxygen desaturations (p=0.001) and 1 arousal (p > 0.05). No apneas were followed by desaturation and arousal. Hypopneas were the most frequent respiratory event and occurred primarily during sleep stage 1 and 2. In all FD-patients, we recorded 362 hypopneas with subsequent oxygen-desaturation that were followed by only 51 arousals. 12 hypopneas (p < 0.001) occurred in 3 controls (p=0.085) and were followed by 3 arousals (p=0.002)

OBJECTIVE: Congenital insensitivity to pain with anhidrosis (CIPA) is caused by mutations in the NKTR1 gene. This affects the development of nerve growth factor (NGF)-dependent neurons including sympathetic cholinergic neurons in the skin, causing anhidrosis. Cardiovascular and blood pressure regulation appears normal, but the integrity of sympathetic adrenergic neurons has not been tested. METHODS: We examined the effect of posture on blood pressure, heart rate, plasma concentration of catecholamines, vasopressin, endothelin, and renin activity in 14 patients with CIPA, 10 patients with chronically deficient sympathetic activity (pure autonomic failure), and 15 normal age-matched controls. RESULTS: In all 14 patients with CIPA, plasma norepinephrine levels were very low or undetectable and failed to increase when the patient was upright, yet upright blood pressure was well maintained. Plasma epinephrine levels were normal and increased when the patient was upright. Plasma renin activity also increased appropriately when the patient was upright and after furosemide-induced volume depletion. Nitric oxide-mediated endothelial function was intact. Patients with pure autonomic failure also had very low levels of plasma norepinephrine both supine and upright, but in contrast to patients with CIPA failed to maintain blood pressure upright. INTERPRETATION: The results indicate that postganglionic sympathetic neurons are severely depleted in CIPA, but chromaffin cells of the adrenal medulla are spared. This confirms the differential effect of NGF signaling for sympathetic neural and chromaffin cell development. The finding that patients with CIPA maintain blood pressure well on standing challenges current concepts of the role of norepinephrine in the regulation of arterial pressure. Ann Neurol 2015;77:743-752.

Hereditary sensory and autonomic neuropathy type III (HSAN III, Riley-Day syndrome, Familial Dysautomia) is characterised by elevated thermal thresholds and an indifference to pain. Using microelectrode recordings we recently showed that these patients possess no functional stretch-sensitive mechanoreceptors in their muscles (muscle spindles), a feature that may explain their lack of stretch reflexes and ataxic gait, yet patients have apparently normal low-threshold cutaneous mechanoreceptors. The density of C-fibres in the skin is markedly reduced in patients with HSAN III, but it is not known whether the C-tactile afferents, a distinct type of low-threshold C fibre present in hairy skin that is sensitive to gentle stroking and has been implicated in the coding of pleasant touch are specifically affected in HSAN III patients. We addressed the relationship between C-tactile afferent function and pleasant touch perception in 15 patients with HSAN III and 15 age-matched control subjects. A soft make-up brush was used to apply stroking stimuli to the forearm and lateral aspect of the leg at five velocities: 0.3, 1, 3, 10 and 30cm/s. As demonstrated previously, the control subjects rated the slowest and highest velocities as less pleasant than those applied at 1-10cm/s, which fits with the optimal velocities for exciting C-tactile afferents. Conversely, for the patients, ratings of pleasantness did not fit the profile for C-tactile afferents. Patients either rated the higher velocities as more pleasant than the slow velocities, with the slowest velocities being rated unpleasant, or rated all velocities equally pleasant. We interpret this to reflect absent or reduced C-tactile afferent density in the skin of patients with HSAN III, who are likely using tactile cues (i.e. myelinated afferents) to rate pleasantness of stroking or are attributing pleasantness to this type of stimulus irrespective of velocity.

To define the retinal phenotype of subjects with familial dysautonomia (FD). A cross-sectional study was carried out in 90 subjects divided in three groups of 30 each (FD subjects, asymptomatic carriers and controls). The study was developed at the Dysautonomia Center, New York University Medical Center. All subjects underwent spectral domain optical coherence tomography (OCT) and full neuro-ophthalmic examinations. In a subset of affected subjects, visual evoked potentials and microperimetry were also obtained. We compared the retinal nerve fiber layer (RNFL) thickness from OCT between the three groups. OCT showed loss of the RNFL in all FD subjects predominantly in the maculopapillary region (63 % temporally, p < 0.0001; and 21 % nasally, p < 0.005). RNFL loss was greatest in older FD subjects and was associated with decreased visual acuity and color vision, central visual field defects, temporal optic nerve pallor, and delayed visual evoked potentials. Asymptomatic carriers of the FD gene mutation all had thinner RNFL (12 % globally, p < 0.005). OCT and clinical neuro-ophthalmological findings suggest that maculopapillary ganglion cells are primarily affected in FD subjects, leading to a specific optic nerve damage that closely resembles mitochondrial optic neuropathies. This raises the possibility that reduced IKAP levels may affect mitochondrial proteins and their function in the nervous system, particularly in the retina.

Familial dysautonomia (FD) is caused by a splicing error in the IKBKAP gene that encodes human Elongator protein-1 (ELP-1). In these patients, exon 20 is frequently skipped duringmRNA splicing, but cells retain the ability to produce a lowlevel of normal (wild-type) IKBKAPmRNAand normal protein. Phosphatidylserine (PS, Sharp-thought), an acidic phospholipid, has been shown to raise elongator protein-1 levels by increasing IKBKAPtranscription in fibroblast cell-lines derived fromFD patients and, more recently, in a mouse model of FD. Given that PS is available over the counter, weconducted a study to determinewhether PS raises IKBKAP gene expression in patients with FD. We enrolled 7 patients with FD, 16-23 years old, in an open-label titration protocol. Patients were examined at baseline (visit 1), after 2 months of taking 300 mg/day (visit 2) and again after 2 months of taking 600 mg/day of PS(visit 3).Bloodwas taken at each visit. Sampleswere de-identified and investigators blinded to the sample identity. Blood was treated with Tri- Reagent, and RNA extracted according to manufacturers specifications. Quantitative polymerase chain reaction (qPCR) was performed to measure the level of normal IKBKAPmRNA. PSwas well tolerated and there were no adverse events or unexpected laboratory abnormalities. After 2 months of taking 300 mg of PS per day, there was a trend for IKBKAP mRNA levels to increase. After 2 months of 600 mg of PS per day, IKBKAPmRNAexpression increased between 2 and 8 fold in all but one patient (p<0.01). Our results indicate that PS safely raises wild-type IKBKAP mRNA levels in blood from patients with FD, opening an exciting potential therapeutic path for treatment. Clinical trials to determine whether restoring Elongator protein 1 levels impacts the phenotype are underway

BACKGROUND: Hereditary sensory and autonomic neuropathy type III features marked ataxic gait that progressively worsens over time. We assessed whether proprioceptive disturbances can explain the ataxia. METHODS: Proprioception at the knee joint was assessed using passive joint angle matching in 18 patients and 14 age-matched controls; 5 patients with cerebellar ataxia were also studied. Ataxia was quantified using the Brief Ataxia Rating Score, which ranged from 7 to 26 of 30. RESULTS: Neuropathy patients performed poorly in judging joint position: mean absolute error was 8.7 degrees +/- 1.0 degrees , and the range was very wide (2.8 degrees -18.1 degrees ); conversely, absolute error was only 2.7 degrees +/- 0.3 degrees (1.6 degrees -5.5 degrees ) in the controls and 3.0 degrees +/- 0.2 degrees (2.1 degrees -3.4 degrees ) in the cerebellar patients. This error was positively correlated to the degree of ataxia in the neuropathy patients but not the cerebellar patients. CONCLUSIONS: These results suggest that poor proprioceptive acuity at the knee joint is a major contributor to the ataxic gait associated with hereditary sensory and autonomic neuropathy type III.

OBJECTIVE: The purpose of this study was to determine whether carbidopa (Lodosyn), an inhibitor of dopa-decarboxylase that blocks the synthesis of dopamine outside the brain, is an effective antiemetic in patients with familial dysautonomia (FD) and hyperdopaminergic nausea/retching/vomiting attacks. METHODS: We enrolled 12 patients with FD in an open-label titration and treatment study to assess the safety of carbidopa. We then conducted a randomized, double-blind, placebo-controlled, crossover study to evaluate its antiemetic efficacy. RESULTS: Previous fundoplication surgery in each patient studied prevented vomiting, but all of the subjects experienced severe cyclical nausea and uncontrollable retching that was refractory to standard treatments. Carbidopa at an average daily dose of 480 mg (range 325-600 mg/day) was well tolerated. In the double-blind phase, patients experienced significantly less nausea and retching while on carbidopa than on placebo (p < 0.03 and p < 0.02, respectively). Twenty-four-hour urinary dopamine excretion was significantly lower while on carbidopa (147 +/- 32 microg/gCr) than while on placebo (222 +/- 41microg/gCr, p < 0.05). CONCLUSIONS: Carbidopa is a safe and effective antiemetic in patients with FD, likely by reducing the formation of dopamine outside the brain. CLASSIFICATION OF EVIDENCE: This study provides Class II evidence that carbidopa is effective in reducing nausea/retching/vomiting in patients with FD.

Genetic disorders affecting the autonomic nervous system can result in abnormal development of the nervous system or they can be caused by neurotransmitter imbalance, an ion-channel disturbance or by storage of deleterious material. The symptoms indicating autonomic dysfunction, however, will depend upon whether the genetic lesion has disrupted peripheral or central autonomic centers or both. Because the autonomic nervous system is pervasive and affects every organ system in the body, autonomic dysfunction will result in impaired homeostasis and symptoms will vary. The possibility of genetic confirmation by molecular testing for specific diagnosis is increasing but treatments tend to remain only supportive and directed toward particular symptoms.