Familial Dysautonomia Research Articles

Frequency and Burden of Gastrointestinal Symptoms in Patients With Familial Dysautonomia

Introduction: Familial dysautonomia (FD) is a rare hereditary neuropathy caused by a mutation in the IKBKAP gene. Despite sensory impairments, patients with FD report a range of gastrointestinal symptoms. As the type and frequency of GI disorders has never been systematically studied, we aimed to establish the frequency of GI symptoms in FD patients relative to the average US population, with the long-term goal of gaining mechanistic insight into the cause of GI symptoms in FD and potentially broader populations. Methods: We distributed a modified version of the validated GI National Institute of Health (NIH) PROMIS questionnaire to 202 FD patients from the NYU FD Registry (the largest known prospective registry). The survey included 61 questions of eight domains (swallowing, nausea, constipation, fecal incontinence, diarrhea, belly pain, reflux, bloating). In addition, participants were asked to identify which bodily system was associated with the most bothersome symptoms, and their use of gastrostomy tubes, which are commonly used in FD patients. The questionnaire was completed by patients, or when appropriate by their primary caregivers. Raw PROMIS scores were normalized against a published validation cohort of 1177 American adults representative of the general population. Results: Seventy-nine (40%) of surveys were returned, with 53% completed by patients directly. Median age of subjects was 24 years old, and 53% were female (Table 1). A quarter of patients received nutrition by gastrostomy solely, while 53% were reliant on them only for liquid intake. Demographics and G tube use were similar between survey responders and non-responders from the FD registry. GI symptoms were more bothersome (42%) than orthopedic (23%), respiratory (14%), visual (13%), or psychiatric (4%) manifestations of the disease. In the previous week, 42% of patients reported watery or loose stools, 25% reported fecal incontinence, 52% reported nausea, and 52% reported borborygmus (Figure 1). Compared to the average American population (mean age 46), patients with FD reported more frequent and severe gastrointestinal symptoms of incontinence, nausea, bloating, and diarrhea (all in second highest quartile) (Figure 2).474_A Figure 1. Demographics. This is a representative sample of the demographics contained in the FD registry.474_B Figure 2. Percentages of FD patients (n=79) reporting gastrointestinal symptoms within the last seven days.Conclusion: Our results show that despite a variety of significant disease complications, GI symptoms are most commonly identified as the worst problem among FD patients. Further research is needed to better understand the underlying mechanism of these GI symptoms in order to improve quality of life.474_C Figure 3. Comparison of severity and frequency of gastrointestinal complaints in FD patients (n=79) versus average American population (n=1177).

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.

Retina-specific loss of Ikbkap/Elp1 causes mitochondrial dysfunction that leads to selective retinal ganglion cell degeneration in a mouse model of familial dysautonomia.

ABSTRACTFamilial dysautonomia (FD) is an autosomal recessive disorder marked by developmental and progressive neuropathies. It is caused by an intronic point-mutation in the IKBKAP/ELP1 gene, which encodes the inhibitor of κB kinase complex-associated protein (IKAP, also called ELP1), a component of the elongator complex. Owing to variation in tissue-specific splicing, the mutation primarily affects the nervous system. One of the most debilitating hallmarks of FD that affects patients' quality of life is progressive blindness. To determine the pathophysiological mechanisms that are triggered by the absence of IKAP in the retina, we generated retina-specific Ikbkap conditional knockout (CKO) mice using Pax6-Cre, which abolished Ikbkap expression in all cell types of the retina. Although sensory and autonomic neuropathies in FD are known to be developmental in origin, the loss of IKAP in the retina did not affect its development, demonstrating that IKAP is not required for retinal development. The loss of IKAP caused progressive degeneration of retinal ganglion cells (RGCs) by 1 month of age. Mitochondrial membrane integrity was breached in RGCs, and later in other retinal neurons. In Ikbkap CKO retinas, mitochondria were depolarized, and complex I function and ATP were significantly reduced. Although mitochondrial impairment was detected in all Ikbkap-deficient retinal neurons, RGCs were the only cell type to degenerate; the survival of other retinal neurons was unaffected. This retina-specific FD model is a useful in vivo model for testing potential therapeutics for mitigating blindness in FD. Moreover, our data indicate that RGCs and mitochondria are promising targets.

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

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

Blocking of an intronic splicing silencer completely rescues IKBKAP exon 20 splicing in familial dysautonomia patient cells.

Familial dysautonomia (FD) is a severe genetic disorder causing sensory and autonomic dysfunction. It is predominantly caused by a c.2204+6T>C mutation in the IKBKAP gene. This mutation decreases the 5′ splice site strength of IKBKAP exon 20 leading to exon 20 skipping and decreased amounts of full-length IKAP protein. We identified a binding site for the splicing regulatory protein hnRNP A1 downstream of the IKBKAP exon 20 5′-splice site. We show that hnRNP A1 binds to this splicing regulatory element (SRE) and that two previously described inhibitory SREs inside IKBKAP exon 20 are also bound by hnRNP A1. Knockdown of hnRNP A1 in FD patient fibroblasts increases IKBKAP exon 20 inclusion demonstrating that hnRNP A1 is a negative regulator of IKBKAP exon 20 splicing. Furthermore, by mutating the SREs in an IKBKAP minigene we show that all three SREs cause hnRNP A1-mediated exon repression. We designed splice switching oligonucleotides (SSO) that blocks the intronic hnRNP A1 binding site, and demonstrate that this completely rescues splicing of IKBKAP exon 20 in FD patient fibroblasts and increases the amounts of IKAP protein. We propose that this may be developed into a potential new specific treatment of FD.

Characteristics of ataxic gait in familial dysautonomia patients.

Introduction and objectivesProgressive ataxic gait is a common symptom in individuals with Familial Dysautonomia (FD). At least 50% of adults with FD require assistance with walking. Our aims were to describe the medical condition of individuals with FD (ii) compare their gait characteristics to healthy individuals, and (iii) assess correlations between gait measures, presence of unstable gait pattern and frequency of falls.MethodsTwelve subjects with FD (7 males, age 25.3±10.6 years) and 16 healthy participants (6 males, age 35.9±11.9 years) were recruited. Gait kinematics, gait symmetry, dynamic muscle activity, and foot deep vibration sensation were recorded.ResultsAtaxic gait degrees were: severe (6 out of 12), moderate (4 out of 12) and low (2 out of 12). The number of falls correlated with base width asymmetry. Crouch gait was noted in 3 out of 12 of the subjects.ConclusionsIn-depth quantitative gait analysis of individuals with FD revealed ataxic gait. The ataxic pattern might be a result of combined neurological deficiencies and osseous deformities. Increasing the base of support of patients with FD might increase the symmetry of the base width during gait and decrease the number of falls. Additionally, perturbation treatment and dynamic balance exercises may be recommended in order to improve compensatory strategies. Future investigation of this population should include quantification of osseous rotations of the lower limb in order to fully understand its effect on their gait pattern and falls.

Exon-specific U1 snRNAs improve ELP1 exon 20 definition and rescue ELP1 protein expression in a familial dysautonomia mouse model.

Familial dysautonomia (FD) is a rare genetic disease with no treatment, caused by an intronic point mutation (c.2204+6T>C) that negatively affects the definition of exon 20 in the elongator complex protein 1 gene (ELP1 also known as IKBKAP). This substitution modifies the 5′ splice site and, in combination with regulatory splicing factors, induces different levels of exon 20 skipping, in various tissues. Here, we evaluated the therapeutic potential of a novel class of U1 snRNA molecules, exon-specific U1s (ExSpeU1s), in correcting ELP1 exon 20 recognition. Lentivirus-mediated expression of ELP1-ExSpeU1 in FD fibroblasts improved ELP1 splicing and protein levels. We next focused on a transgenic mouse model that recapitulates the same tissue-specific mis-splicing seen in FD patients. Intraperitoneal delivery of ELP1-ExSpeU1s-adeno-associated virus particles successfully increased the production of full-length human ELP1 transcript and protein. This splice-switching class of molecules is the first to specifically correct the ELP1 exon 20 splicing defect. Our data provide proof of principle of ExSpeU1s-adeno-associated virus particles as a novel therapeutic strategy for FD.

Antisense oligonucleotides correct the familial dysautonomia splicing defect in IKBKAP transgenic mice.

Familial dysautonomia (FD) is a rare inherited neurodegenerative disorder caused by a point mutation in the IKBKAP gene that results in defective splicing of its pre-mRNA. The mutation weakens the 5′ splice site of exon 20, causing this exon to be skipped, thereby introducing a premature termination codon. Though detailed FD pathogenesis mechanisms are not yet clear, correcting the splicing defect in the relevant tissue(s), thus restoring normal expression levels of the full-length IKAP protein, could be therapeutic. Splice-switching antisense oligonucleotides (ASOs) can be effective targeted therapeutics for neurodegenerative diseases, such as nusinersen (Spinraza), an approved drug for spinal muscular atrophy. Using a two-step screen with ASOs targeting IKBKAP exon 20 or the adjoining intronic regions, we identified a lead ASO that fully restored exon 20 splicing in FD patient fibroblasts. We also characterized the corresponding cis-acting regulatory sequences that control exon 20 splicing. When administered into a transgenic FD mouse model, the lead ASO promoted expression of full-length human IKBKAP mRNA and IKAP protein levels in several tissues tested, including the central nervous system. These findings provide insights into the mechanisms of IKBKAP exon 20 recognition, and pre-clinical proof of concept for an ASO-based targeted therapy for FD.

Female-Specific Association Between Variants on Chromosome 9 and Self-Reported Diagnosis of Irritable Bowel Syndrome

Genetic factors are believed to affect risk for irritable bowel syndrome (IBS), but there have been no sufficiently powered and adequately sized studies. To identify DNA variants associated with IBS risk, we performed a genome-wide association study (GWAS) of the large UK Biobank population-based cohort, which includes genotype and health data from 500,000 participants. We studied 7,287,191 high-quality single nucleotide polymorphisms in individuals who self-reported a doctor's diagnosis of IBS (cases; n= 9576) compared to the remainder of the cohort (controls; n= 336,499) (mean age of study subjects, 40-69 years). Genome-wide significant findings were further investigated in 2045 patients with IBS from tertiary centers and 7955 population controls from Europe and the United States, and a small general population sample from Sweden (n= 249). Functional annotation of GWAS results was carried out by integrating data from multiple biorepositories to obtain biological insights from the observed associations. We identified a genome-wide significant association on chromosome 9q31.2 (single nucleotide polymorphism rs10512344; P= 3.57× 10-8) in a region previously linked to age at menarche, and 13 additional loci of suggestive significance (P < 5.0×10-6). Sex-stratified analyses revealed that the variants at 9q31.2 affect risk of IBS in women only (P= 4.29× 10-10 in UK Biobank) and also associate with constipation-predominant IBS in women (P=.015 in the tertiary cohort) and harder stools in women (P= .0012 in the population-based sample). Functional annotation of the 9q31.2 locus identified 8 candidate genes, including the elongator complex protein 1 gene (ELP1 or IKBKAP), which is mutated in patients with familial dysautonomia. In a sufficiently powered GWAS of IBS, we associated variants at the locus 9q31.2 with risk of IBS in women. This observation may provide additional rationale for investigating the role of sex hormones and autonomic dysfunction in IBS.

When PNS Assembly Goes Awry: Familial Dysautonomia

Over a century of elegant work has contributed to our understanding of how neural crest cells migrate throughout the embryo to give rise to the majority of cell types in the peripheral nervous system (PNS). This rich foundation is the basis for our lab's investigation of the cellular and molecular mechanisms that go awry to result in the developmental disorder of the PNS, Familial dysautonomia (FD). Three of the key clinical hallmarks of FD include a reduction in pain and temperature sensation, misregulation of the sympathetic nervous system, and impaired gastrointestinal tract function. The neurons in all of these systems derive from the neural crest. Consequently, a prevailing hypothesis in the field was that FD resulted from faulty neural crest migration. To test this hypothesis, we generated mice in which the gene that is mutated to cause FD, IKBKAP/ELP1, was deleted selectively from the neural crest. Interestingly, by the end of embryogenesis, we found that in fact the number of pain and temperature receptors in the dorsal root ganglia were significantly reduced as were sympathetic neurons in the superior cervical ganglia, recapitulating the human disease phenotype (George et al., 2013, PNAS). However, these studies also demonstrated that this selective reduction in neuronal number was not due to faulty neural crest cell migration. Rather, the reductions were due to (1) the death and premature differentiation of the Pax3+ pain and temperature progenitor cells and (2) exacerbated apoptosis of TrkA+ pain and temperature receptors. Interestingly, the TrkC+ proprioceptors developed normally, although they later die progressively in adulthood (Elisabetta Morini and Susan Slaughenhaupt, personal communication). Upon the completion of neurogenesis in the dorsal root and sympathetic ganglia, PNS axons must innervate their targets to fully differentiate. Our work and others (Jackson et al., 2014, Development; Abashidze et al., 2015, PLoS One) demonstrate that IkbkapElp1 is required for normal axon outgrowth and target innervation. These and other findings for how and why PNS development is disrupted in FD will be discussed.Support or Funding InformationNIH R01 NS086796; Dysautonomia FoundationThis abstract is from the Experimental Biology 2018 Meeting. There is no full text article associated with this abstract published in The FASEB Journal.

Elp1‐dependent Shp1 Phosphatase Regulation and its Essential Role in Familial Dysautonomia Pathogenesis

Familial Dysautonomia (FD; Riley‐Day Syndrome; HSAN3) is a rare heritable disease characterized by debilitating sensory and sympathetic neuropathy. It is caused by a germline mutation of the Elp1 gene that leads to exon mis‐splicing, nonsense‐mediated truncation of the Elp1 protein and loss of Elp1 protein primarily in sympathetic and nociceptive sensory neurons. How Elp1 functions in FD disease‐vulnerable neurons is very poorly understood.Using Elp1 conditional knockout mice that we generated to recapitulate the molecular and physiologic phenotypes associated with human FD, we identified abnormalities in sympathetic neurons that explain the pathophysiologic basis for disease. Sympathetic neurons isolated from Elp1 conditional knockout mice have abnormalities in nerve growth factor signaling which is essential for their survival. NGF is normally acquired from peripheral tissues by innervating axons and NGF retrograde signal transduction to the neuron cell body is essential for their normal survival and differentiation. We found that sympathetic neurons lacking Elp1 have abnormalities in retrograde NGF signaling and as a consequence they have impaired survival and differentiation in response to NGF. After binding to NGF, the terminal axon TrkA (NTRK1) receptors are internalized and phosphorylated to activate downstream signaling pathways essential for sympathetic neuron survival and differentiation. We found that Elp1‐ deficient neurons normally bind NGF and they normally internalize and activate (phosphorylate) TrkA receptors in response to NGF. However in the absence of Elp1, TrkA receptor phosphorylation, which is essential for activation and downstream signaling, was markedly diminished. Shp1 phosphatase, which normally binds to TrkA receptors and terminates signaling by dephosphorylation, was found to be hyperactivated in the absence of Elp1. Shp1 hyperactivation results in precocious TrkA receptor dephosphorylation and attenuation of retrograde signaling. Pharmacological treatment with either Shp1 phosphatase inhibitors or molecular inhibition of Shp1 phosphatase activity resulted in complete rescue of TrkA dephosphorylation and restoration of normal NGF‐dependent retrograde neuron survival.These results demonstrate that sympathetic neuron death in patients with FD is due to loss for normal retrograde NGF signaling mediated by Shp1 phosphatase hyperactivity and precocious attenuation of TrkA signaling. Inhibition of Shp1 phosphatase activity may provide a novel therapy for sympathetic neuron loss in FD. Future studies are focused on understanding how Elp1 regulates Shp1 phosphatase activity and whether it may regulate Shp1 phosphatase activity in other signal transduction pathways involved in immune function and oncogenesis.Support or Funding InformationSupport: NIH: NICHD, NINDS and NOD.This abstract is from the Experimental Biology 2018 Meeting. There is no full text article associated with this abstract published in The FASEB Journal.

Elongator complex is required for long-term olfactory memory formation in Drosophila.

The evolutionarily conserved Elongator Complex associates with RNA polymerase II for transcriptional elongation. Elp3 is the catalytic subunit, contains histone acetyltransferase activity, and is associated with neurodegeneration in humans. Elp1 is a scaffolding subunit and when mutated causes familial dysautonomia. Here, we show that elp3 and elp1 are required for aversive long-term olfactory memory in Drosophila. RNAi knockdown of elp3 in adult mushroom bodies impairs long-term memory (LTM) without affecting earlier forms of memory. RNAi knockdown with coexpression of elp3 cDNA reverses the impairment. Similarly, RNAi knockdown of elp1 impairs LTM and coexpression of elp1 cDNA reverses this phenotype. The LTM deficit in elp3 and elp1 knockdown flies is accompanied by the abolishment of a LTM trace, which is registered as increased calcium influx in response to the CS+ odor in the α-branch of mushroom body neurons. Coexpression of elp1 or elp3 cDNA rescues the memory trace in parallel with LTM. These data show that the Elongator complex is required in adult mushroom body neurons for long-term behavioral memory and the associated long-term memory trace.

Elongator and codon bias regulate protein levels in mammalian peripheral neurons

Familial dysautonomia (FD) results from mutation in IKBKAP/ELP1, a gene encoding the scaffolding protein for the Elongator complex. This highly conserved complex is required for the translation of codon-biased genes in lower organisms. Here we investigate whether Elongator serves a similar function in mammalian peripheral neurons, the population devastated in FD. Using codon-biased eGFP sensors, and multiplexing of codon usage with transcriptome and proteome analyses of over 6,000 genes, we identify two categories of genes, as well as specific gene identities that depend on Elongator for normal expression. Moreover, we show that multiple genes in the DNA damage repair pathway are codon-biased, and that with Elongator loss, their misregulation is correlated with elevated levels of DNA damage. These findings link Elongator’s function in the translation of codon-biased genes with both the developmental and neurodegenerative phenotypes of FD, and also clarify the increased risk of cancer associated with the disease.

Ambulatory blood pressure profiles in familial dysautonomia.

Familial dysautonomia (FD) is a rare genetic disease that involves extreme blood pressure fluctuations secondary to afferent baroreflex failure. The diurnal blood pressure profile, including the average, variability, and day-night difference, may have implications for long-term end organ damage. The purpose of this study was to describe the circadian pattern of blood pressure in the FD population and relationships with renal and pulmonary function, use of medications, and overall disability. We analyzed 24-h ambulatory blood pressure monitoring recordings in 22 patients with FD. Information about medications, disease severity, renal function (estimated glomerular filtration, eGFR), pulmonary function (forced expiratory volume in 1s, FEV1) and an index of blood pressure variability (standard deviation of systolic pressure) were analyzed. The mean (±SEM) 24-h blood pressure was 115±5.6/72±2.0mmHg. The diurnal blood pressure variability was high (daytime systolic pressure standard deviation 22.4±1.5mmHg, nighttime 17.2±1.6), with a high frequency of a non-dipping pattern (16 patients, 73%). eGFR, use of medications, FEV1, and disability scores were unrelated to the degree of blood pressure variability or to dipping status. This FD cohort had normal average 24-h blood pressure, fluctuating blood pressure, and a high frequency of non-dippers. Although there was evidence of renal dysfunction based on eGFR and proteinuria, the ABPM profile was unrelated to the measures of end organ dysfunction or to reported disability.

Prevalence and characteristics of sleep-disordered breathing in familial dysautonomia

ObjectiveFamilial 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/MethodsSeventy-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. ResultsOverall, 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. ConclusionMost 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.

Structural insights into the function of Elongator.

Conserved from yeast to humans, Elongator is a protein complex implicated in multiple processes including transcription regulation, α-tubulin acetylation, and tRNA modification, and its defects have been shown to cause human diseases such as familial dysautonomia. Elongator consists of two copies of six core subunits (Elp1, Elp2, Elp3, Elp4, Elp5, and Elp6) that are organized into two subcomplexes: Elp1/2/3 and Elp4/5/6 and form a stable assembly of~850kDa in size. Although the catalytic subunit of Elongator is Elp3, which contains a radical S-adenosyl-L-methionine (SAM) domain and a putative histone acetyltransferase domain, the Elp4/5/6 subcomplex also possesses ATP-modulated tRNA binding activity. How at the molecular level, Elongator performs its multiple functions and how the different subunits regulate Elongator's activities remains poorly understood. Here, we provide an overview of the proposed functions of Elongator and describe how recent structural studies provide new insights into the mechanism of action of this multifunctional complex.

Patient-Derived Induced Pluripotent Stem Cells for Alpha-1 Antitrypsin Deficiency Disease Modeling and Therapeutic Discovery.

PIZZ alpha-1 antitrypsin deficiency (AATD) is an autosomal recessive disease affecting approximately 100,000 individuals in the United States and one of the most common hereditary causes of liver disease.1 The most common form of the disease results from a single base pair mutation (Glu342Lys), known as the "Z" mutation, that encodes a mutant protein (Z alpha-1 antritypsin [AAT]) that is prone to misfolding and is retained in the endoplasmic reticulum (ER) rather than appropriately secreted. Some of the retained mutant protein attains an unusual aggregated or polymerized conformation. Retained polymeric ZAAT aggregates are hepatotoxic and lead to downstream liver disease in a subset of PiZZ neonates and adults through a gain-of-function mechanism. PiZZ individuals are likewise highly predisposed to developing chronic obstructive pulmonary disease (COPD)/emphysema as a result of low circulating levels of AAT protein and associated protease-antiprotease imbalance. Much of our understanding of the molecular pathogenesis of AATD is based on studies employing either transgenic mice that express the mutant human Z allele or immortalized cell lines transduced to overexpress ZAAT. While they have been quite informative, these models fail to capture the patient-to-patient variability in disease phenotype that clinicians observe in their AATD patients, raising the question of whether alternative models might provide new insight. Induced pluripotent stem cells (iPSCs), first described in 2006, have the capacity to differentiate into a broad array of cell types from all 3 germ layers, including hepatocytes. Disease-specific iPSCs have been derived from patients with a variety of monogenic disorders and have been found to faithfully recapitulate features of such diseases as spinal muscular atrophy, familial dysautonomia, Rett syndrome, polycythemia vera, type 1A glycogen storage disease, familial hypercholesterolemia, long QT syndrome, and others. This discussion reviews the potential applications of iPSCs for understanding AATD-associated liver disease as well as for development of potential therapeutic strategies.

Fludrocortisone for orthostatic hypotension

Background Orthostatic hypotension is an excessive fall in blood pressure (BP) while standing and is the result of a decrease in cardiac output or defective or inadequate vasoconstrictor mechanisms. Fludrocortisone is a mineralocorticoid that increases blood volume and blood pressure. Fludrocortisone is considered the first- or second-line pharmacological therapy for orthostatic hypotension alongside mechanical and positional measures such as increasing fluid and salt intake and venous compression methods. However, there has been no Cochrane Review of the benefits and harms of this drug for this condition. Objectives To identify and evaluate the benefits and harms of fludrocortisone for orthostatic hypotension. Search methods We searched the following databases on 11 November 2019: Cochrane Neuromuscular Specialised Register, CENTRAL, MEDLINE, Embase and CINAHL. We also searched trials registries. Selection criteria We included all studies evaluating the benefits and harms of fludrocortisone compared to placebo, another drug for orthostatic hypotension, or studies without comparators, including randomized controlled trials (RCTs), quasi-RCTs and observational studies. We included studies in people with orthostatic hypotension due to a chronic peripheral neuropathy, a central autonomic neuropathy, or autonomic failure from other causes, but not medication-induced orthostatic hypotension or orthostatic hypotension from acute volume depletion or blood loss. Data collection and analysis We used Cochrane methodological procedures for most of the review. We developed and used a tool to prioritize observational studies that offered the best available evidence where there are gaps in the evidence from RCTs. We assessed the certainty of evidence for fludrocortisone versus placebo using GRADE. Main results We included 13 studies of 513 participants, including three cross-over RCTs and 10 observational studies (three cohort studies, six case series and one case-control study). The included RCTs were small (total of 28 participants in RCTs), short term (two to three weeks), only examined fludrocortisone for orthostatic hypotension in people with two conditions (diabetes and Parkinson disease), and had variable risk of bias (two had unclear risk of bias and one had low risk of bias). Heterogeneity in participant populations, comparators and outcome assessment methods prevented meta-analyses of the RCTs. We found very low-certainty evidence about the effects of fludrocortisone versus placebo on drop in BP in people with diabetes (-26 mmHg versus -39 mmHg systolic; -7 mmHg versus -11 mmHg diastolic; 1 cross-over study, 6 participants). For people with Parkinson disease, we found very-low certainty evidence about the effects of fludrocortisone on drop in BP compared to pyridostigmine (-14 mmHg versus -22.1 mmHg diastolic; P = 0.036; 1 cross-over study, 9 participants) and domperidone (no change after treatment in either group; 1 cross-over study, 13 participants). For orthostatic symptoms, we found very low-certainty evidence for fludrocortisone versus placebo in people with diabetes (4 out of 5 analyzed participants had improvements in orthostatic symptoms, 1 cross-over study, 6 participants), for fludrocortisone versus pyridostigmine in people with Parkinson disease (orthostatic symptoms unchanged; 1 cross-over study, 9 participants) or fludrocortisone versus domperidone (improvement to 6 for both interventions on the Composite Autonomic Symptom Scale-Orthostatic Domain (COMPASS-OD); 1 cross-over study, 13 participants). Evidence on adverse events was also very low-certainty in both populations, but indicated side effects were minimal. Observational studies filled some gaps in evidence by examining the effects in larger groups of participants, with more diverse conditions, over longer periods of time. One cohort study (341 people studied retrospectively) found fludrocortisone may not be harmful in the long term for familial dysautonomia. However, it is unclear if this translates to long-term improvements in BP drop or a meaningful improvement in orthostatic symptoms. Authors' conclusions The evidence is very uncertain about the effects of fludrocortisone on blood pressure, orthostatic symptoms or adverse events in people with orthostatic hypotension and diabetes or Parkinson disease. There is a lack of information on long-term treatment and treatment of orthostatic hypotension in other disease states. There is a need for standardized reporting of outcomes and for standardization of measurements of blood pressure in orthostatic hypotension.

IKBKAP/ELP1 gene mutations: mechanisms of familial dysautonomia and gene-targeting therapies.

The successful completion of the Human Genome Project led to the discovery of the molecular basis of thousands of genetic disorders. The identification of the mutations that cause familial dysautonomia (FD), an autosomal recessive disorder that impacts sensory and autonomic neurons, was aided by the release of the human DNA sequence. The identification and characterization of the genetic cause of FD have changed the natural history of this disease. Genetic testing programs, which were established shortly after the disease-causing mutations were identified, have almost completely eliminated the birth of children with this disorder. Characterization of the principal disease-causing mutation has led to the development of therapeutic modalities that ameliorate its effect, while the development of mouse models that recapitulate the impact of the mutation has allowed for the in-depth characterization of its impact on neuronal development and survival. The intense research focus on this disorder, while clearly benefiting the FD patient population, also serves as a model for the positive impact focused research efforts can have on the future of other genetic diseases. Here, we present the research advances and scientific breakthroughs that have changed and will continue to change the natural history of this centuries-old genetic disease.

Founder mutation in IKBKAP gene causes vestibular impairment in familial dysautonomia

ObjectiveTo 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. MethodsCervical 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. ResultscVEMP 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. ConclusionsThe founder mutation in the IKBKAP gene affects the development of vestibular afferent pathways, leading to attenuated cVEMPs. SignificanceVestibular abnormalities may contribute to the gait ataxia in FD.