Localization of the gene for familial dysautonomia on chromosome 9 and definition of DNA markers for genetic diagnosis

Sensorimotor control in the congenital absence of functional muscle spindles

Hereditary sensory and autonomic neuropathy type III (HSAN III), also known as familial dysautonomia or Riley-Day syndrome, results from an autosomal recessive genetic mutation that causes a selective loss of specific sensory neurones, leading to greatly elevated pain and temperature thresholds, poor proprioception, marked ataxia and disturbances in blood pressure control. Stretch reflexes are absent throughout the body, which can be explained by the absence of functional muscle spindle afferents - assessed by intraneural microelectrodes inserted into peripheral nerves in the upper and lower limbs. This also explains the greatly compromised proprioception at the knee joint, as assessed by passive joint-angle matching. Moreover, there is a tight correlation between loss of proprioceptive acuity at the knee and the severity of gait impairment. Surprisingly, proprioception is normal at the elbow, suggesting that participants are relying more on sensory cues from the overlying skin; microelectrode recordings have shown that myelinated tactile afferents in the upper and lower limbs appear to be normal. Nevertheless, the lack of muscle spindles does affect sensorimotor control in the upper limb: in addition to poor performance in the finger-to-nose test, manual performance in the Purdue pegboard task is much worse than in age-matched healthy controls. Unlike those rare individuals with large-fibre sensory neuropathy, in which both muscle spindle and cutaneous afferents are absent, those with HSAN III present as a means of assessing sensorimotor control following the selective loss of muscle spindle afferents.

Strategies for targeting RNA with small molecule drugs

INTRODUCTION

Historically, therapeutic treatment of disease has been restricted to targeting proteins. Of the approximately 20,000 translated human proteins, approximately 1600 are associated with diseases. Strikingly, less than 15% of disease-associated proteins are predicted or known to be 'druggable.' While the concept and narrative of protein druggability continue to evolve with the development of novel technological and pharmacological advances, most of the human proteome remains undrugged. Recent genomic studies indicate that less than 2% of the human genome encodes for proteins, and while as much as 75% of the genome is transcribed, RNA has largely been ignored as a druggable target for therapeutic interventions.

AREAS COVERED

This review delineates the theory and techniques involved in the development of small molecule inhibitors of RNAs from brute force, high-throughput screening technologies to de novo molecular design using computational machine and deep learning. We will also highlight the potential pitfalls and limitations of targeting RNA with small molecules.

EXPERT OPINION

Although significant advances have recently been made in developing systems to identify small molecule inhibitors of RNAs, many challenges remain. Focusing on RNA structure and ligand binding sites may help bring drugging RNA in line with traditional protein drug targeting.

Rescue of a familial dysautonomia mouse model by AAV9-Exon-specific U1 snRNA

Familial dysautonomia (FD) is a currently untreatable, neurodegenerative disease caused by a splicing mutation (c.2204+6T>C) that causes skipping of exon 20 of the elongator complex protein 1 (ELP1) pre-mRNA. Here, we used adeno-associated virus serotype 9 (AAV9-U1-FD) to deliver an exon-specific U1 (ExSpeU1) small nuclear RNA, designed to cause inclusion of ELP1 exon 20 only in those cells expressing the target pre-mRNA, in a phenotypic mouse model of FD. Postnatal systemic and intracerebral ventricular treatment in these mice increased the inclusion of ELP1 exon 20. This also augmented the production of functional protein in several tissues including brain, dorsal root, and trigeminal ganglia. Crucially, the treatment rescued most of the FD mouse mortality before one month of age (89% vs 52%). There were notable improvements in ataxic gait as well as renal (serum creatinine) and cardiac (ejection fraction) functions. RNA-seq analyses of dorsal root ganglia from treated mice and human cells overexpressing FD-ExSpeU1 revealed only minimal global changes in gene expression and splicing. Overall then, our data prove that AAV9-U1-FD is highly specific and will likely be a safe and effective therapeutic strategy for this debilitating disease.

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.

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.

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.

Familial dysautonomia: History, genotype, phenotype and translational research

Familial dysautonomia (FD) is a rare neurological disorder caused by a splice mutation in the IKBKAP gene. The mutation arose in the 1500s within the small Jewish founder population in Eastern Europe and became prevalent during the period of rapid population expansion within the Pale of Settlement. The carrier rate is 1:32 in Jews descending from this region. The mutation results in a tissue-specific deficiency in IKAP, a protein involved in the development and survival of neurons. Patients homozygous for the mutations are born with multiple lesions affecting mostly sensory (afferent) fibers, which leads to widespread organ dysfunction and increased mortality. Neurodegenerative features of the disease include progressive optic atrophy and worsening gait ataxia. Here we review the progress made in the last decade to better understand the genotype and phenotype. We also discuss the challenges of conducting controlled clinical trials in this rare medically fragile population. Meanwhile, the search for better treatments as well as a neuroprotective agent is ongoing.

Familial Dysautonomia (FD) Human Embryonic Stem Cell Derived PNS Neurons Reveal that Synaptic Vesicular and Neuronal Transport Genes Are Directly or Indirectly Affected by IKBKAP Downregulation

A splicing mutation in the IKBKAP gene causes Familial Dysautonomia (FD), affecting the IKAP protein expression levels and proper development and function of the peripheral nervous system (PNS). Here we found new molecular insights for the IKAP role and the impact of the FD mutation in the human PNS lineage by using a novel and unique human embryonic stem cell (hESC) line homozygous to the FD mutation originated by pre implantation genetic diagnosis (PGD) analysis. We found that IKBKAP downregulation during PNS differentiation affects normal migration in FD-hESC derived neural crest cells (NCC) while at later stages the PNS neurons show reduced intracellular colocalization between vesicular proteins and IKAP. Comparative wide transcriptome analysis of FD and WT hESC-derived neurons together with the analysis of human brains from FD and WT 12 weeks old embryos and experimental validation of the results confirmed that synaptic vesicular and neuronal transport genes are directly or indirectly affected by IKBKAP downregulation in FD neurons. Moreover we show that kinetin (a drug that corrects IKBKAP alternative splicing) promotes the recovery of IKAP expression and these IKAP functional associated genes identified in the study. Altogether, these results support the view that IKAP might be a vesicular like protein that might be involved in neuronal transport in hESC derived PNS neurons. This function seems to be mostly affected in FD-hESC derived PNS neurons probably reflecting some PNS neuronal dysfunction observed in FD.

Increased frequency of rhabdomyolysis in familial dysautonomia

INTRODUCTION

Familial dysautonomia (FD; OMIM # 223900) is an autosomal recessive disease with features of impaired pain and temperature perception and lack of functional muscle spindles. After 3 FD patients presented with rhabdomyolysis in a short time span, we aimed to determine the frequency of rhabdomyolysis is this population.

METHODS

This study was a retrospective chart review of 665 FD patients.

RESULTS

Eight patients had at least 1 episode of rhabdomyolysis. Two patients had 2 episodes. The average incidence of rhabdomyolysis in FD was 7.5 per 10,000 person-years. By comparison, the average incidence with statins has been reported to be 0.44 per 10,000 person-years. Mean maximum creatine kinase (CK) level was 32,714 ± 64,749 U/L. Three patients had hip magnetic resonance imaging showing gluteal hyperintensities.

CONCLUSIONS

Patients with FD have an increased incidence of rhabdomyolysis. We hypothesize that this may result from a combination of absent functional muscle spindles and muscle mitochondrial abnormalities.

Contemporary perioperative management of adult familial dysautonomia (Riley-Day syndrome)

Familial dysautonomia (Riley-Day syndrome) is a rare multisystem disorder associated with an excess risk of perioperative morbidity and mortality. Because life expectancy is limited, few reports consider the perioperative management of familial dysautonomia in adults with advanced disease and end-organ dysfunction. Here, we report on the management of an adult patient with familial dysautonomia, highlighting recent developments in perioperative technology and pharmacology of special relevance to this challenging population.

Current treatments in familial dysautonomia

INTRODUCTION

Familial dysautonomia (FD) is a rare hereditary sensory and autonomic neuropathy (type III). The disease is caused by a point mutation in the IKBKAP gene that affects the splicing of the elongator-1 protein (ELP-1) (also known as IKAP). Patients have dramatic blood pressure instability due to baroreflex failure, chronic kidney disease, and impaired swallowing leading to recurrent aspiration pneumonia, which results in chronic lung disease. Diminished pain and temperature perception result in neuropathic joints and thermal injuries. Impaired proprioception leads to gait ataxia. Optic neuropathy and corneal opacities lead to progressive visual loss.

AREAS COVERED

This article reviews current therapeutic strategies for the symptomatic treatment of FD, as well as the potential of new gene-modifying agents.

EXPERT OPINION

Therapeutic focus on FD is centered on reducing the catecholamine surges caused by baroreflex failure. Managing neurogenic dysphagia with effective protection of the airway passages and prompt treatment of aspiration pneumonias is necessary to prevent respiratory failure. Sedative medications should be used cautiously due to the risk of respiratory depression. Non-invasive ventilation during sleep effectively manages apneas and prevents hypercapnia. Clinical trials of compounds that increase levels of IKAP (ELP-1) are underway and will determine whether they can reverse or slow disease progression.

Disturbances in affective touch in hereditary sensory & autonomic neuropathy type III

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 30 cm/s. As demonstrated previously, the control subjects rated the slowest and highest velocities as less pleasant than those applied at 1–10 cm/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.

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C-tactile afferents in hairy skin are believed to mediate affective touch.

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They are sensitive to slow brushing stimuli, which are perceived as pleasant.

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It is not known whether C-tactile afferents are affected in HSAN III.

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Ratings of pleasantness were reduced in 15 HSAN III patients compared to controls.

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We suggest that the density of C-tactile afferents is reduced in HSAN III.

BCL9 and C9orf5 are associated with negative symptoms in schizophrenia: meta-analysis of two genome-wide association studies

Schizophrenia is a chronic and debilitating psychiatric condition affecting slightly more than 1% of the population worldwide and it is a multifactorial disorder with a high degree of heritability (80%) based on family and twin studies. Increasing lines of evidence suggest intermediate phenotypes/endophenotypes are more associated with causes of the disease and are less genetically complex than the broader disease spectrum. Negative symptoms in schizophrenia are attractive intermediate phenotypes based on their clinical and treatment response features. Therefore, our objective was to identify genetic variants underlying the negative symptoms of schizophrenia by analyzing two genome-wide association (GWA) data sets consisting of a total of 1,774 European-American patients and 2,726 controls. Logistic regression analysis of negative symptoms as a binary trait (adjusted for age and sex) was performed using PLINK. For meta-analysis of two datasets, the fixed-effect model in PLINK was applied. Through meta-analysis we identified 25 single nucleotide polymorphisms (SNPs) associated with negative symptoms with p<5×10(-5). Especially we detected five SNPs in the first two genes/loci strongly associated with negative symptoms of schizophrenia (P(meta-analysis)<6.22×10(-6)), which included three SNPs in the BCL9 gene: rs583583 showed the strongest association at a P(meta-analysis) of 6.00×10(-7) and two SNPs in the C9orf5 (the top SNP is rs643410 with a p = 1.29 ×10(-6)). Through meta-analysis, we identified several additional negative symptoms associated genes (ST3GAL1, RNF144, CTNNA3 and ZNF385D). This is the first report of the common variants influencing negative symptoms of schizophrenia. These results provide direct evidence of using of negative symptoms as an intermediate phenotype to dissect the complex genetics of schizophrenia. However, additional studies are warranted to examine the underlying mechanisms of these disease-associated SNPs in these genes.

Hereditary sensory and autonomic neuropathies

Hereditary sensory and autonomic neuropathies (HSN/HSAN) are clinically and genetically heterogeneous disorders of the peripheral nervous system that predominantly affect the sensory and autonomic neurons. Hallmark features comprise not only prominent sensory signs and symptoms and ulcerative mutilations but also variable autonomic and motor disturbances. Autosomal dominant and autosomal recessive inheritance has been reported. Molecular genetics studies have identified disease-causing mutations in 11 genes. Some of the affected proteins have nerve-specific roles but underlying mechanisms have also been shown to involve sphingolipid metabolism, vesicular transport, structural integrity, and transcription regulation. Genetic and functional studies have substantially improved the understanding of the pathogenesis of the HSN/HSAN and will help to find preventive and causative therapies in the future.

Familial dysautonomia (Riley-Day syndrome): when baroreceptor feedback fails

Familial dysautonomia (FD) is a rare hereditary disorder caused by mutations within the gene that encodes for I-κ-B kinase complex associated protein (IKAP). A deficiency of IKAP affects the development of primary sensory neurons including those carrying baroreflex afferent volleys, a feature that explains their characteristic sensory loss and labile blood pressure. This review describes the history, the genotype of FD and the unusual cardiovascular autonomic phenotype of these patients. We outline the main consequences of a failure to receive information from arterial baroreceptors, including the characteristic "autonomic storms" and severe end-organ target damage.

Cardiac-locked bursts of muscle sympathetic nerve activity are absent in familial dysautonomia

Familial dysautonomia (Riley-Day syndrome) is an hereditary sensory and autonomic neuropathy (HSAN type III), expressed at birth, that is associated with reduced pain and temperature sensibilities and absent baroreflexes, causing orthostatic hypotension as well as labile blood pressure that increases markedly during emotional excitement. Given the apparent absence of functional baroreceptor afferents, we tested the hypothesis that the normal cardiac-locked bursts of muscle sympathetic nerve activity (MSNA) are absent in patients with familial dysautonomia. Tungsten microelectrodes were inserted percutaneously into muscle or cutaneous fascicles of the common peroneal nerve in 12 patients with familial dysautonomia. 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 a manoeuvre that unloads the baroreceptors. Conversely, skin sympathetic nerve activity (SSNA), recorded in four patients, appeared normal. We conclude that the loss of phasic bursts of MSNA and the loss of baroreflex modulation of muscle vasoconstrictor drive contributes to the poor control of blood pressure in familial dysautonomia, and that the increase in tonic firing of muscle vasoconstrictor neurones contributes to the increase in blood pressure during emotional excitement.

Clinical neuro-ophthalmic findings in familial dysautonomia

BACKGROUND

To define the clinical neuro-ophthalmic abnormalities of patients with familial dysautonomia (FD).

METHODS

Sixteen patients (32 eyes) with the clinical and molecular diagnoses of FD underwent thorough neuro-ophthalmic clinical evaluation.

RESULTS

Visual acuity ranged from 0.05 to 1.0 decimal units and was reduced in 15 of 16 patients. Mild to moderate corneal opacities were found in most patients but were visually significant in only 2 eyes. Red-green color vision was impaired in almost all cases. Depression of the central visual fields was present on automated visual fields in all patients, even in those with normal visual acuity. Temporal optic nerve pallor was present in all cases and was associated with retinal nerve fiber layer loss in the papillomacular region. Various ocular motility abnormalities also were observed.

CONCLUSION

Patients with FD have a specific type of optic neuropathy with predominant loss of papillomacular nerve fibers, a pattern similar to other hereditary optic neuropathies caused by mutations either in nuclear or in mitochondrial DNA, affecting mitochondrial protein function. Defects of eye movements, particularly saccades, also appear to be a feature of patients with FD.

Can loss of muscle spindle afferents explain the ataxic gait in Riley-Day syndrome?

The Riley-Day syndrome is the most common of the hereditary sensory and autonomic neuropathies (Type III). Among the well-recognized clinical features are reduced pain and temperature sensation, absent deep tendon reflexes and a progressively ataxic gait. To explain the latter we tested the hypothesis that muscle spindles, or their afferents, are absent in hereditary sensory and autonomic neuropathy III by attempting to record from muscle spindle afferents from a nerve supplying the leg in 10 patients. For comparison we also recorded muscle spindles from 15 healthy subjects and from two patients with hereditary sensory and autonomic neuropathy IV, who have profound sensory disturbances but no ataxia. Tungsten microelectrodes were inserted percutaneously into fascicles of the common peroneal nerve at the fibular head. Intraneural stimulation within muscle fascicles evoked twitches at normal stimulus currents (10-30 µA), and deep pain (which often referred) at high intensities (1 mA). Microneurographic recordings from muscle fascicles revealed a complete absence of spontaneously active muscle spindles in patients with hereditary sensory and autonomic neuropathy III; moreover, responses to passive muscle stretch could not be observed. Conversely, muscle spindles appeared normal in patients with hereditary sensory and autonomic neuropathy IV, with mean firing rates of spontaneously active endings being similar to those recorded from healthy controls. Intraneural stimulation within cutaneous fascicles evoked paraesthesiae in the fascicular innervation territory at normal stimulus intensities, but cutaneous pain was never reported during high-intensity stimulation in any of the patients. Microneurographic recordings from cutaneous fascicles revealed the presence of normal large-diameter cutaneous mechanoreceptors in hereditary sensory and autonomic neuropathy III. Our results suggest that the complete absence of functional muscle spindles in these patients explains their loss of deep tendon reflexes. Moreover, we suggest that their ataxic gait is sensory in origin, due to the loss of functional muscle spindles and hence a compromised sensorimotor control of locomotion.

Modeling neurological disorders by human induced pluripotent stem cells

Studies of human brain development are critical as research on neurological disorders have been progressively advanced. However, understanding the process of neurogenesis through analysis of the early embryo is complicated and limited by a number of factors, including the complexity of the embryos, availability, and ethical constrains. The emerging of human embryonic stem cells (hESCs) and induced pluripotent stem cells (iPSCs) has shed light of a new approach to study both early development and disease pathology. The cells behave as precursors of all embryonic lineages; thus, they allow tracing the history from the root to individual branches of the cell lineage tree. Systems for neural differentiation of hESCs and iPSCs have provided an experimental model that can be used to augment in vitro studies of in vivo brain development. Interestingly, iPSCs derived from patients, containing donor genetic background, have offered a breakthrough approach to study human genetics of neurodegenerative diseases. This paper summarizes the recent reports of the development of iPSCs from patients who suffer from neurological diseases and evaluates the feasibility of iPSCs as a disease model. The benefits and obstacles of iPSC technology are highlighted in order to raising the cautions of misinterpretation prior to further clinical translations.

Limited atlantooccipital and cervical range of motion in patients with familial dysautonomia

Familial dysautonomia (FD) is a rare neurological disease with autosomal recessive inheritance and is associated with severe kyphoscoliosis. Investigators have reported subjective observation of decreased cervical motion and high rates of proximal instrumentation failure in this population. A radiographic study of sagittal plane cervical spine motion was performed with 15 patients with FD. Measurements were compared with normal values. Patients with FD had decreased sagittal motion at all cervical levels (P<0.05). Intervertebral translation was also decreased significantly at C3-C6. FD is associated with decreased sagittal motion in the cervical spine.

Pharmacogenetics in pain management: the clinical need

Genetic research heralds a new therapeutic approach to pain management. Increasing literature demonstrates individual genetic vulnerabilities to specific pain types and mechanisms, partially explaining differing responses to similar pain stimuli. Furthermore, analgesics demonstrate great variability among polymorphic genotypes. Family history and genotyping promise to play an important role in future pain therapies. As advances continue in the genetics of pain and analgesia, pharmacotherapy will depend more on an individualized, targeted approach and less on empiricism.

Peripheral arthropathy in hereditary sensory and autonomic neuropathy types III and IV

BACKGROUND

To determine the features of the underlying destructive arthropathy in the peripheral joints of children with hereditary sensory and autonomic neuropathy (HSAN) type III and to compare and contrast this to the arthropathy noted in HSAN type IV, as both groups experience decreased pain perception.

METHODS

From a database of 547 patients with HSAN type III and 32 patients with HSAN type IV, we performed a retrospective chart review and radiographic analysis of all patients who presented with joint swelling and deformity. Underlying joint pathology was classified as either osteonecrosis or Charcot arthropathy.

RESULTS

In the HSAN type III population, 44 (8%; 22 males and 22 females) of the 547 patients had clinical evidence of arthropathy. In 42 patients, 48 joints demonstrated radiographic evidence of osteonecrosis; 45 (94%) of the 48 joints with osteonecrosis occurred in the lower extremity. In each case of osteonecrosis of the knee (n = 19), isolated involvement of the lateral distal femoral condyle was seen consisting of varying sizes of posterolateral osteochondral fragmentation. In the 32 patients comprising the HSAN type IV population, 18 (56%) were found to have radiographic findings consistent with Charcot arthropathy in a total of 30 affected joints. One patient demonstrated Charcot arthropathy of the spine and subsequent progressive spondylolisthesis. Nine patients (12 joints) also demonstrated osteomyelitis.

CONCLUSIONS

In patients with HSAN type III, osteonecrosis is the initial lesion preceding destructive arthropathy. Osteonecrosis and osteochondral fragmentation were always isolated at the lateral distal femoral condyle in the knee. This pathology may be amenable to surgical reconstruction and fixation to stabilize the knee and prevent further degeneration. Hereditary sensory and autonomic neuropathy type IV was most commonly associated with Charcot arthropathy or joint subluxation and dislocation. Late secondary changes at the articular surface may make radiographic distinction difficult. Charcot arthropathy affected both sides of the involved joint with evidence of collapse and fragmentation. With osteonecrosis, the articular process was found to be more focal.

Genetic mutations that prevent pain: implications for future pain medication

Part of the interindividual variability in pain therapy has been associated with genetic polymorphisms. Several genetic variants prevent or at least decrease pain in their carriers as compared with carriers of the respective wild-type or common alleles by impeding the generation, transmission and processing of nociceptive information or by increasing the local availability of active analgesics or their pharmacodynamic effects. Complete prevention of pain has so far been seen in six distinct rare hereditary syndromes, namely the ‘channelopathy-associated insensitivity to pain’, caused by 13 currently identified variants in the SCN9A gene coding for the α-subunit of the voltage-gated sodium channel, and five maladies belonging to the hereditary sensory and autonomic neuropathy (HSAN) I–V syndromes, caused by various mutations in several genes. Reduced pain in the average population has been associated with frequent variants in the µ-opioid receptor gene (OPRM1), catechol-O-methyltransferase gene (COMT), guanosine triphosphate cyclohydrolase 1/dopa-responsive dystonia gene (GCH1), transient receptor potential cation channel, subfamily V, member 1 gene (TRPV1) or the melanocortin-1 receptor gene (MC1R). Duplications/amplifications of the cytochrome P450 2D6 (CYP2D6) gene leading to increased enzyme function may cause intense opioid effects of codeine up to toxicity. The COMT V158M variant has been associated with decreased morphine requirements for analgesia. Inactivating MC1R variants have been associated with increased opioid analgesia of the µ-opioid receptor agonist morphine-6-glucuronide and, in women only, of κ-opioid agonists. Finally, variants in the P-glycoprotein gene (ABCB1) conferring decreased transporter function have been associated with increased respiratory depressive effects of fentanyl. In summary, a finite number of genetic variants that prevent pain by decreasing nociception or increasing analgesia have been identified. Given the complex biological and psychological nature of pain, we will see in the near future how much of the interindividual variance in pain and analgesia is due to identifiable genetic causes, and to what extent genetics enters clinical pain therapy.

Short-chain acyl-CoA dehydrogenase gene mutation (c.319C>T) presents with clinical heterogeneity and is candidate founder mutation in individuals of Ashkenazi Jewish origin

We report 10 children (7 male, 3 female), 3 homozygous for c.319C>T mutation and 7 heterozygous for c.319C>T on one allele and c.625G>A variant on the other in the short-chain acyl-CoA dehydrogenase (SCAD) gene (ACADS). All were of Ashkenazi Jewish origin in which group we found a c.319C>T heterozygote frequency of 1:15 suggesting the presence of a founder mutation or selective advantage. Phenotype was variable with onset from birth to early childhood. Features included hypotonia (8/10), developmental delay (8/10), myopathy (4/10) with multicore changes in two and lipid storage in one, facial weakness (3/10), lethargy (5/10), feeding difficulties (4/10) and congenital abnormalities (3/7). One female with multiminicore myopathy had progressive external ophthalmoplegia, ptosis and cardiomyopathy with pneumonia and respiratory failure. Two brothers presented with psychosis, pyramidal signs, and multifocal white matter abnormalities on MRI brain suggesting additional genetic factors. Two other infants also had white matter changes. Elevated butyrylcarnitine (4/8), ethylmalonic aciduria (9/9), methylsuccinic aciduria (6/7), decreased butyrate oxidation in lymphoblasts (2/4) and decreased SCAD activity in fibroblasts or muscle (3/3) were shown. Expression studies of c.319C>T in mouse liver mitochondria showed it to be inactivating. c.625G>A is a common variant in ACADS that may confer disease susceptibility. Five healthy parents were heterozygous for c.319C>T and c.625G>A, suggesting reduced penetrance or broad clinical spectrum. We conclude that the c.319C>T mutation can lead to wide clinical and biochemical phenotypic variability, suggesting a complex multifactorial/polygenic condition. This should be screened for in individuals with multicore myopathy, particularly among the Ashkenazim.

The molecular basis of familial dysautonomia: overview, new discoveries and implications for directed therapies

Familial dysautonomia (FD) is a sensory and autonomic neuropathy that affects the development and survival of sensory, sympathetic, and some parasympathetic neurons. It is autosomally inherited and occurs almost exclusively among individuals of Ashkenazi Jewish descent. The pathological and clinical manifestations of FD have been extensively studied and therapeutic modalities have, until recently, focused primarily on addressing the symptoms experienced by those with this fatal disorder. The primary FD-causing mutation is an intronic nucleotide substitution that alters the splicing of the IKBKAP-derived transcript. Recent efforts have resulted in the development of new therapeutic modalities that facilitate the increased production of the correctly spliced transcript and mitigate the symptoms of those with FD. Furthermore, the recent demonstration of the reduced presence of monoamine oxidase A in cells and tissues of individuals with FD has provided new insight into the cause of hypertensive crises experienced by these patients.

Hereditary sensory and autonomic neuropathies: types II, III, and IV

The hereditary sensory and autonomic neuropathies (HSAN) encompass a number of inherited disorders that are associated with sensory dysfunction (depressed reflexes, altered pain and temperature perception) and varying degrees of autonomic dysfunction (gastroesophageal reflux, postural hypotention, excessive sweating). Subsequent to the numerical classification of four distinct forms of HSAN that was proposed by Dyck and Ohta, additional entities continue to be described, so that identification and classification are ongoing. As a group, the HSAN are rare diseases that affect both sexes. HSAN III is almost exclusive to individuals of Eastern European Jewish extraction, with incidence of 1 per 3600 live births. Several hundred cases with HSAN IV have been reported. The worldwide prevalence of HSAN type II is very low. This review focuses on the description of three of the disorders, HSAN II through IV, that are characterized by autosomal recessive inheritance and onset at birth. These three forms of HSAN have been the most intensively studied, especially familial dysautonomia (Riley-Day syndrome or HSAN III), which is often used as a prototype for comparison to the other HSAN. Each HSAN disorder is likely caused by different genetic errors that affect specific aspects of small fiber neurodevelopment, which result in variable phenotypic expression. As genetic tests are routinely used for diagnostic confirmation of HSAN III only, other means of differentiating between the disorders is necessary. Diagnosis is based on the clinical features, the degree of both sensory and autonomic dysfunction, and biochemical evaluations, with pathologic examinations serving to further confirm differences. Treatments for all these disorders are supportive.

Molecular genetics of hereditary sensory neuropathies

Hereditary sensory neuropathies (HSN), also known as hereditary sensory and autonomic neuropathies (HSAN), are a clinically and genetically heterogeneous group of disorders. They are caused by neuronal atrophy and degeneration, predominantly affecting peripheral sensory and autonomic neurons. Both congenital and juvenile to adulthood onset is possible. Currently, the classification of the HSN depends on the mode of inheritance, age at onset, and clinical presentation. Hallmark features are progressive sensory loss, chronic skin ulcers, and other skin abnormalities. Spontaneous fractures and neuropathic arthropathy are frequent complications and often necessitate amputations. Autonomic features vary between different subgroups. Distal muscle weakness and wasting may be present and is sometimes so prominent that it becomes difficult to distinguish HSN from Charcot-Marie-Tooth syndrome. Recent major advances in molecular genetics have led to the identification of seven gene loci and six-disease causing genes for autosomal-dominant and autosomal-recessive HSN. These genes have been shown to play roles in lipid metabolism and the regulation of intracellular vesicular transport, but also a presumptive transcriptional regulator, a nerve growth factor receptor, and a nerve growth factor have been described among the causative genes in HSN. Nevertheless, it remains unclear how mutations in the known genes lead to the phenotype of HSN. In this review, we summarize the recent progress of the molecular genetics of the HSN and the implicated genes.

Autonomic Peripheral Neuropathy

Most generalized peripheral polyneuropathies are accompanied by clinical or subclinical autonomic dysfunction. There is a group of peripheral neuropathies in which the small or unmyelinated fibers are selectively targeted. In these neuropathies, autonomic dysfunction is the most prominent manifestation. The features associated with an autonomic neuropathy include impairment of cardiovascular, gastrointestinal, urogenital, thermoregulatory, sudomotor, and pupillomotor autonomic function.

Therapeutic potential and mechanism of kinetin as a treatment for the human splicing disease familial dysautonomia

Mutations that affect the splicing of pre-mRNA are a major cause of human disease. Familial dysautonomia (FD) is a recessive neurodegenerative disease caused by a T to C transition at base pair 6 of IKBKAP intron 20. This mutation results in variable tissue-specific skipping of exon 20. Previously, we reported that the plant cytokinin kinetin dramatically increases exon 20 inclusion in RNA isolated from cultured FD cells. The goal of the current study was to investigate the nature of the FD splicing defect and the mechanism by which kinetin improves exon inclusion, as such knowledge will facilitate the development of future therapeutics aimed at regulating mRNA splicing. In this study, we demonstrate that treatment of FD lymphoblast cell lines with kinetin increases IKBKAP mRNA and IKAP protein to normal levels. Using a series of minigene constructs, we show that deletion of a region at the end of IKBKAP exon 20 disrupts the ability of kinetin to improve exon inclusion, pinpointing a kinetin responsive sequence element. We next performed a screen of endogenously expressed genes with multiple isoforms resulting from exon skipping events and show that kinetin's ability to improve exon inclusion is not limited to IKBKAP. Lastly, we highlight the potential of kinetin for the treatment of other human splicing disorders by showing correction of a splicing defect in neurofibromatosis.

Anesthesia management of familial dysautonomia

Familial dysautonomia (FD) is an autosomal recessive inherited disorder, predominantly affecting the Ashkenazi Jewish population that is characterized by sensory and autonomic neuropathy. The protean manifestations and perturbations result in high morbidity and mortality. However, as a result of supportive measures and centralized care, survival has improved. As surgical options are increasing to symptomatically treat FD, anesthesiologists need to be familiar with this disorder. Because the Dysautonomia Center at NYU Medical Center is a referral center for FD patients, we have attained considerable anesthetic experience with FD. This article reviews clinical features of FD that could potentially affect anesthetic management and outlines our present practices.

Familial dysautonomia: a review of the current pharmacological treatments

Treatment of familial dysautonomia, a genetic disorder affecting neuronal development and survival, has improved morbidity and survival for this disorder. Although this is primarily a neurological disorder causing sensory and autonomic dysfunction, there are secondary systemic perturbations affecting ophthalmological, gastrointestinal, respiratory, cardiovascular, orthopaedic and renal function. Penetrance is complete, but there is marked variability in expression. Preventative and supportive treatments have included measures to maintain eye moisture, fundoplication with gastrostomy, the use of central agents such as benzodiazepines and clonidine to control vomiting and the dysautonomic crisis, and fludrocortisone and midodrine to combat cardiovascular lability. With the identification of the familial dysautonomia gene, it has been suggested that it may be possible to treat patients by modifying production and expression of the genetic product.

Charcot-Marie-Tooth disease (hereditary motor sensory neuropathies) and hereditary sensory and autonomic neuropathies

BACKGROUND

Since the description of Charcot-Marie-Tooth disease over a century ago. it has now been recognized that these conditions are not caused by generalized metabolic defects but rather have various discrete genetic origins. These disorders can also have variable phenotypes due to dysfunction of peripheral nerve axons or their myelin due to the genetic defects that affect the formation of specific nerve proteins.

REVIEW SUMMARY

This article summarizes the clinical presentation of various phenotypes of the hereditary motor sensory neuropathies and the hereditary sensory and autonomic neuropathies, genetic mutations, and their relevant protein products. Proper identification of the genetic defects provides the opportunity for better genetic counseling and hopefully therapies in the future.

Episodic somnolence in an infant with Riley-Day syndrome

Familial dysautonomia is an autosomal recessive congenital neuropathy that occurs almost exclusively in the Ashkenazi Jewish population and has rarely been diagnosed in the neonatal period in unaffected families. This report describes a patient who, during the neonatal period, had episodes of marked decrease in the level of consciousness with durations of 4-15 hours. Other signs and symptoms included the absence of fungiform papillae of the tongue, areflexia, and failure to thrive. The diagnosis was confirmed by the demonstration of mutations in the IkappaB kinase complex-associated protein gene with the identification of IVS20 (+6T --> C) which is responsible for more than 99.5% of known Ashkenazi Jewish patients with familial dysautonomia. The prognosis of this disease and the possibility of genetic counseling are clearly related with an early definitive diagnosis, and this patient illustrates the importance of episodes of somnolence as a possible sign of familial dysautonomia.

The effect of hereditary disorders on tooth components: a radiographic morphometric study of two syndromes

OBJECTIVE

The purpose of this study was to compare tooth components (enamel and dentin) in Familial Dysautonomia (FD) and Down syndrome (DS) in order to assess the extent to which each was affected.

DESIGN

The design was cross-sectional. The sample consisted of 20 FD patients and 45 DS patients. The control group comprised 250 healthy subjects. Mesio-distal crown width (CW), enamel and dentin thickness and pulp chamber dimensions were measured on standardized bitewing radiographs of mandibular second primary and first permanent molars. Statistical analyses were performed between groups using SAS programs.

RESULTS

CW was reduced in both hereditary disorders. In the DS group enamel height (EH) and dentin thickness were reduced. In FD enamel thickness in the primary and permanent molars as well as dentin height (DH) in permanent molars was increased.

CONCLUSIONS

In both syndromes the reduction in CW suggests reduced proliferation during tooth germ formation. However, the differences in enamel and dentin thickness suggest that ameloblasts and odontoblasts were affected differently in the later phases of cell function. In FD cell function is stimulated resulting in thicker enamel and dentin. In DS cell function is reduced resulting in thin enamel and dentin.

Decreased density of ganglia and neurons in the myenteric plexus of familial dysautonomia patients

BACKGROUND

Familial dysautonomia (FD) is a hereditary disease of the autonomic and sensory nervous system. A prominent manifestation of FD is gastrointestinal dyscoordination, which contributes to the morbidity and mortality in FD.

AIM

As the myenteric plexus is an essential factor in gastrointestinal motility control, we compared its morphology in appendices of FD patients and controls.

METHODS

Appendices from FD patients (N=19) were obtained during surgery of fundoplication and gastrostomy; normal appendices (N=17) were obtained from patients suspected to suffer from acute appendicitis, in whom, however, the appendix was found to be normal. Specimens were stained histochemically for NADPH diaphorase (NADPH-d) and in a blinded manner examined under a light microscope for seven morphologic parameters: ganglionic density, neuronal density, ganglionic area, number of stained neurons per ganglion, nerve bundle width, ratio between nervous tissue area and total area, and neuronal area.

RESULTS

Ganglionic density was 10.13 per mm(2) in controls versus 5.01 per mm(2) in FD (p<0.05). Neuronal density was 70.12 per mm(2) in controls, compared with 22.09 per mm(2) in FD (p<0.01). The other parameters were not different between the two groups.

CONCLUSION

Densities of myenteric ganglia and neurons of FD patients were significantly lower than in controls. This deficiency may contribute to the pathogenesis of FD gastroenteropathy.

Familial dysautonomia

Familial dysautonomia (FD) is a neurodevelopmental genetic disorder within the larger classification of hereditary sensory and autonomic neuropathies, each caused by a different genetic error. The FD gene has been identified as IKBKAP. Mutations result in tissue-specific expression of mutant IkappaB kinase-associated protein (IKAP). The genetic error probably affects development, as well as maintenance, of neurons because there is neuropathological and clinical progression. Pathological alterations consist of decreased unmyelinated and small-fiber neurons. Clinical features reflect widespread involvement of sensory and autonomic neurons. Sensory loss includes impaired pain and temperature appreciation. Autonomic features include dysphagia, vomiting crises, blood pressure lability, and sudomotor dysfunction. Central dysfunction includes emotional lability and ataxia. With supportive treatment, prognosis has improved greatly. About 40% of patients are over age 20 years. The cause of death is usually pulmonary failure, unexplained sudden deaths, or renal failure. With the discovery of the genetic defect, definitive treatments are anticipated.

Hereditary sensory neuropathy with spastic paraplegia

We report the case of a 4-year-old boy with hereditary sensory neuropathy manifesting as insensitivity to pain in all four limbs and associated with spastic paraplegia. The patient was referred with multiple injuries to his fingers suggestive of self-mutilation and attributed to psychiatric disturbance. Clinical examination corrected the diagnosis by revealing insensitivity to pain in all four limbs, associated with spastic paraplegia. The histamine test reaction was positive, nerve biopsy and electrophysiological investigations confirmed sensory nerve involvement and the diagnosis of hereditary sensory neuropathy. Classification and treatment of such rare diseases is difficult and a multidisciplinary approach is often necessary.

Geographic distribution of disease mutations in the Ashkenazi Jewish population supports genetic drift over selection

The presence of four lysosomal storage diseases (LSDs) at increased frequency in the Ashkenazi Jewish population has suggested to many the operation of natural selection (carrier advantage) as the driving force. We compare LSDs and nonlysosomal storage diseases (NLSDs) in terms of the number of mutations, allele-frequency distributions, and estimated coalescence dates of mutations. We also provide new data on the European geographic distribution, in the Ashkenazi population, of seven LSD and seven NLSD mutations. No differences in any of the distributions were observed between LSDs and NLSDs. Furthermore, no regular pattern of geographic distribution was observed for LSD versus NLSD mutations-with some being more common in central Europe and others being more common in eastern Europe, within each group. The most striking disparate pattern was the geographic distribution of the two primary Tay-Sachs disease mutations, with the first being more common in central Europe (and likely older) and the second being exclusive to eastern Europe (primarily Lithuania and Russia) (and likely much younger). The latter demonstrates a pattern similar to two other recently arisen Lithuanian mutations, those for torsion dystonia and familial hypercholesterolemia. These observations provide compelling support for random genetic drift (chance founder effects, one approximately 11 centuries ago that affected all Ashkenazim and another approximately 5 centuries ago that affected Lithuanians), rather than selection, as the primary determinant of disease mutations in the Ashkenazi population.

Survival in familial dysautonomia: Impact of early intervention

OBJECTIVE

To assess the effectiveness of advances in supportive centralized care on survival and function in patients with familial dysautonomia (FD).

STUDY DESIGN

From September l, 1969 through January 1, 2001. Five hundred fifty-one patients with FD entered the Dysautonomia Center. We divided the group into two cohorts: the first cohort (n = 227) entered until March 1, 1981, and the second cohort (n = 324) entered after March 1, 1981. Survival curves were compared by using log-rank tests. Demographic and disease characteristics were examined, including gender, geographic location, age at entry, birth weight, breath-holding history, age of walking, causes of death, and social data.

RESULTS

For both cohorts age at entry was the primary variable that influenced survival; mortality increased by 3% per year. Survival time lengthened for cohort 2 when survival time was defined as time from entry into the Center to last observation or death; in cohort 2, mortality was 73% that of cohort 1 even after adjustment for age at entry. Although survival improved, causes of death were unchanged; sleep deaths and sudden deaths remained frequent.

CONCLUSION

Our data indicate that the more recent cohort patients were younger at the time of entry and had improved survival, which suggests that early access to centralized and more advanced treatment appreciably benefits patients with familial dysautonomia.

Familial dysautonomia

Familial dysautonomia is a developmental disorder of the sensory and autonomic nervous system. Recent studies have shown that two mutations in the gene IKBKAP are responsible for the disease. IKAP, the IKBKAP-encoded protein, is a member of the recently identified human Elongator complex. The major FD mutation is a splice mutation that results in aberrant tissue-specific mRNA splicing.