Hyperekplexia, a cause of neonatal apnea: a case report

Neonatal Hyperekplexia: Is It Still a Diagnostic Challenge? Evidence From a Systematic Review

Hyperekplexia is a neurologic disorder characterized by an exaggerated startle reflex in response to different types of stimuli. Hyperekplexia is defined by the triad of neonatal hypertonia, excessive startle reflexes, and generalized stiffness following the startle. Although uncommon, hyperekplexia can lead to serious consequences such as falls, brain injury, or sudden infant death syndrome.Aim of this study was to identify cases of neonatal hyperekplexia with a confirmed genetic diagnosis and to establish the genotype-phenotype correlation at onset. Articles were selected from 1993 to 2024 and PRISMA Statement was applied including newborns within 28 days of life. So, we retrieved from literature 14 cases of genetically confirmed neonatal hyperekplexia. The onset of clinical manifestations occurred in the first day of life in 8 of 14 patients (57.14%). Clinical findings were muscle stiffness (100%), startle reflex (66.66%), apnea/cyanosis (41.66%), positive nose-tapping test (33.33%), jerks (33.33%), jitteriness (25%), and ictal blinking (25%). Genes involved were GLRA1 in 9 of 14 (64.28%), SLC6A5 in 2 of 14 (14.28%), GPHN in 1 of 14 (7.14%), and GLRB in 2 of 14 (14.28%). Patients showed heterozygous (66.66%) or homozygous (33.33%) status. In 7 of 14 cases (50%), the condition occurred in other family members. A genotype-phenotype correlation was not achievable.Timely diagnosis is crucial to improve the natural history of hyperekplexia avoiding/reducing possible major complications such as sudden infant death syndrome, brain injury, and serious falls. Early differentiation from epilepsy minimizes treatment cost and improves the quality of life of patients.

Startle Latency as a Potential Marker for Amygdala-Mediated Hyperarousal

BACKGROUND

Fear-related disorders are characterized by hyperexcitability in reflexive circuits and maladaptive associative learning mechanisms. The startle reflex is suited to investigate both processes, either by probing it under baseline conditions or by deriving it in fear conditioning studies. In anxiety research, the amplitude of the fear-potentiated startle has been shown to be influenced by amygdalar circuits and has typically been the readout of interest. In schizophrenia research, prolonged startle peak latency under neutral conditions is an established readout, thought to reflect impaired processing speed. We therefore explored whether startle latency is an informative readout for human anxiety research.

METHODS

We investigated potential similarities and differences of startle peak latency and amplitude derived from a classical fear conditioning task in a sample of 206 participants with varying severity levels of anxiety disorders and healthy control subjects. We first reduced startle response to stable components and regressed individual amygdala gray matter volumes onto the resulting startle measures. We then probed time, stimulus, and group effects of startle latency.

RESULTS

We showed that startle latency and startle amplitude were 2 largely uncorrelated measures; startle latency, but not amplitude, showed a sex-specific association with gray matter volume of the amygdala; startle latencies showed a fear-dependent task modulation; and patients with fear-related disorders displayed shorter startle latencies throughout the fear learning task.

CONCLUSIONS

These data provide support for the notion that probing startle latencies under threat may engage amygdala-modulated threat processing, making them a complementary marker for human anxiety research.

Recommendations for the diagnosis and treatment of paroxysmal kinesigenic dyskinesia: an expert consensus in China

Paroxysmal dyskinesias are a group of neurological diseases characterized by intermittent episodes of involuntary movements with different causes. Paroxysmal kinesigenic dyskinesia (PKD) is the most common type of paroxysmal dyskinesia and can be divided into primary and secondary types based on the etiology. Clinically, PKD is characterized by recurrent and transient attacks of involuntary movements precipitated by a sudden voluntary action. The major cause of primary PKD is genetic abnormalities, and the inheritance pattern of PKD is mainly autosomal-dominant with incomplete penetrance. The proline-rich transmembrane protein 2 (PRRT2) was the first identified causative gene of PKD, accounting for the majority of PKD cases worldwide. An increasing number of studies has revealed the clinical and genetic characteristics, as well as the underlying mechanisms of PKD. By seeking the views of domestic experts, we propose an expert consensus regarding the diagnosis and treatment of PKD to help establish standardized clinical evaluation and therapies for PKD. In this consensus, we review the clinical manifestations, etiology, clinical diagnostic criteria and therapeutic recommendations for PKD, and results of genetic analyses in PKD patients performed in domestic hospitals.

Neurobiology of glycine transporters: From molecules to behavior

Glycine transporters (GlyTs) are Na⁺/Cl^--dependent neurotransmitter transporters, responsible for l-glycine uptake into the central nervous system. GlyTs are members of the solute carrier family 6 (SLC6) and comprise glycine transporter type 1 (SLC6A9; GlyT1) and glycine transporter type 2 (SLC6A5; Glyt2). GlyT1 and GlyT2 are expressed on both astrocytes and neurons, but their expression pattern in brain tissue is foremost related to neurotransmission. GlyT2 is markedly expressed in brainstem, spinal cord and cerebellum, where it is responsible for glycine uptake into glycinergic and GABAergic terminals. GlyT1 is abundant in neocortex, thalamus and hippocampus, where it is expressed in astrocytes, and involved in glutamatergic neurotransmission. Consequently, inhibition of GlyT1 transporters can modulate glutamatergic neurotransmission through NMDA receptors, suggesting an alternative therapeutic strategy. In this review, we focus on recent progress in the understanding of GlyTs role in brain function and in various diseases, such as epilepsy, hyperekplexia, neuropathic pain, drug addiction, schizophrenia and stroke, as well as in neurodegenerative disorders.

Clobazam-clonazepam combination effective for stimulus-induced falling in hyperekplexia

A child with the major form of hyperekplexia is presented who stopped ambulating because of frequent unexpected falls associated with acoustic and visual stimuli. A combination of clobazam and clonazepam was well tolerated and was rapidly and dramatically effective in eliminating the falls and restoring ambulation.

Hyperekplexia: Treatment of a Severe Phenotype and Review of the Literature

Hyperekplexia is a rare disorder caused by autosomal dominant or recessive modes of inheritance and characterized by episodes of exaggerated startle. Five causative genes have been identified to date. The syndrome has been recognized for decades and due to its rarity, the literature contains mostly descriptive reports, many early studies lacking molecular genetic diagnoses. A spectrum of clinical severity exists. Severe cases can lead to neonatal cardiac arrest and death during an episode, an outcome prevented by early diagnosis and clinical vigilance. Large treatment studies are not feasible, so therapeutic measures continue to be empiric. A marked response to clonazepam is often reported but refractory cases exist. Herein we report the clinical course and treatment response of a severely affected infant homozygous for an SLC6A5 nonsense mutation and review the literature summarizing the history and genetic understanding of the disease as well as the described comorbidities and treatment options.

A novel syndrome of lethal familial hyperekplexia associated with brain malformation

Background

Hyperekplexia (HPX) is a rare non-epileptic disorder manifesting immediately after birth with exaggerated persistent startle reaction to unexpected auditory, somatosensory and visual stimuli, and non-habituating generalized flexor spasm in response to tapping of the nasal bridge (glabellar tap) which forms its clinical hallmark. The course of the disease is usually benign with spontaneous amelioration with age. The disorder results from aberrant glycinergic neurotransmission, and several mutations were reported in the genes encoding glycine receptor (GlyR) α1 and β subunits, glycine transporter GlyT2 as well as two other proteins involved in glycinergic neurotransmission gephyrin and collybistin.

Methods

The phenotype of six newborns, belonging to Saudi Arabian kindred with close consanguineous marriages, who presented with hyperekplexia associated with severe brain malformation, is described. DNA samples were available from two patients, and homozygosity scan to determine overlap with known hyperkplexia genes was performed.

Results

The kindred consisted of two brothers married to their cousin sisters, each with three affected children who presented antenatally with excessive fetal movements. Postnatally, they were found to have microcephaly, severe hyperekplexia and gross brain malformation characterized by severe simplified gyral pattern and cerebellar underdevelopment. The EEG was normal and they responded to clonazepam. All of the six patients died within six weeks. Laboratory investigations, including metabolic screen, were unremarkable. None of the known hyperkplexia genes were present within the overlapping regions of homozygosity between the two patients for whom DNA samples were available.

Conclusions

We present these cases as a novel syndrome of lethal familial autosomal recessive hyperekplexia associated with microcephaly and severe brain malformation.

Ectodermal, skeletal, and genitourinary abnormalities with neonatal hyperekplexia

A new syndrome of the major form of hyperekplexia with neonatal onset is described. An infant manifested multisystem involvement with ectodermal anomalies, including lymphedema and double eyelashes (lymphedema-distichiasis syndrome), genitourinary anomalies, and skeletal dysplasia. Despite extensive genetic evaluation, no cytogenetic or molecular etiologies were identified. The literature was reviewed to assess other unusual neurologic and nonneurologic features that have been reported in association with neonatal-onset hyperekplexia-that is, hyperekplexia-plus syndromes.

New treatment paradigms in neonatal metabolic epilepsies

Neonatal seizures represent a major challenge among the epilepsies vis-à-vis seizure classification, electroclinical correlation, inherent excitability of neocortex, ontogenic characteristics of neurotransmitter receptors, and responsiveness to standard antiepileptic drugs. Each of these factors renders neonatal seizures more difficult to treat, and therapy has been a vexing area for recent advances in this seizure category. Conversely, specific metabolic disorders have very special therapeutic considerations in the clinical setting of neonatal seizures which require a high index of clinical suspicion and rapid intervention for a successful outcome. The prototype is pyridoxine dependency, although pyridoxal 5'-phosphate dependency is a recently recognized but treatable neonatal epilepsy that deserves earmarked distinction. Clinicians must remain vigilant for these possibilities, including atypical cases where apparent seizure-free intervals may occur. Folinic acid-dependent seizures are allelic with pyridoxine dependency. Serine-dependent seizures and glucose transporter deficiency may present with neonatal seizures and have specific therapy. A vital potassium channel regulated by serum ATP/ADP ratios in the pancreas and brain may be mutated with a resultant neuroendocrinopathy characterized by development delay, epilepsy, and neonatal diabetes (DEND). This requires oral hypoglycaemic therapy, and not insulin, for neurological responsiveness. The startle syndrome of hyperekplexia, which mimics neonatal epilepsy, has been associated with laryngospasm and sudden death but is treated with benzodiazepines.

Movement disorder emergencies

Movement disorder emergencies include any movement disorder which evolves over hours to days, in which failure to appropriately diagnose and manage can result in patient morbidity or mortality. It is crucial that doctors recognize these emergencies with accuracy and speed by obtaining the proper history and by being familiar with the phenomenology of frequently encountered movements. These disorders will be discussed based on the most common associated involuntary movement, either parkinsonism, dystonia, chorea, tics or myoclonus, and, when available, review the workup and treatment options based on the current literature.

Identification of a de novo Lys304Gln mutation in the glycine receptor alpha-1 subunit gene in a Korean infant with hyperekplexia

Startle disease or hyperekplexia (STHE; MIM 149400) is a rare disorder that is characterized by marked muscular hypertonia in infancy and an exaggerated startle response to unexpected acoustic or tactile stimuli. Mutations in the gene encoding the alpha-1 subunit of the inhibitory glycine receptor (GLRA1) were reported as causes of STHE. Recently, we encountered a Korean male infant with generalized stiffness that was observed from the first 3 days of life. The abnormal startle response was evident from the fourth week of life, and he showed marked improvement in the startle response and muscle hypertonia after being administered phenobarbital and clonazepam. Direct sequencing analysis of the infant and his parents revealed a de novo variation (c.910A>C) in the GLRA1 gene, resulting in a novel Lys304Gln missense mutation.

Congenital hyperekplexia: five sporadic cases

We report fives sporadic cases of hyperekplexia or startle disease characterized by a highly exaggerated startle reflex and tonic attacks. Affected neonates suffer from prolonged periods of stiffness and are at risk for sudden death from apnea. An early diagnosis is needed. Sudden loud sounds, unexpected tactile stimuli or percussion at the base of the nose can also elicit excessive jerking or tonic attack. The diagnosis of hyperekplexia is a purely clinical one. A defect of the alpha1 subunit of inhibitory glycine receptor (GLRA1) has been observed in the dominant form with a mutation in the chromosome 5. Clonazepam is effective and decreases the severity of the symptoms. The disease tends to improve after infancy and the psychomotor development is normal. The major form of "hyperekplexia" should be considered whenever one is confronted with neonatal hypertonicity associated with paroxysmal tonic manifestations (without electroencephalography anomalies).

CONCLUSION

the diagnosis of hyperekplexia should be evaluated in any neonate with tonic attacks without evident cause.

Movement disorder emergencies

For the past 4 years, Dr. Stanley Fahn and I have given a course at the American Academy of Neurology annual meeting on the topic of movement disorder emergencies. The purpose of this review article is to summarize the topic and to present it to readers of this journal. The text of this article has appeared in nearly the same form as the Academy syllabus accompanying our course. It is being presented here so that readers of the journal may review the material.

Sporadic major hyperekplexia in neonates and infants: clinical manifestations and outcome

The aim of the present study is to report on the syndrome of sporadic major hyperekplexia during the neonatal period and early infancy, diagnosed in 39 patients at an average age of 3.3 months, the most severely affected during the first month of life. The patients mainly presented with marked irritability and recurrent startles in response to handling or even minute sounds, accompanied by rhythmic jerky movements and occasionally breath-holding episodes. Family history was negative for hyperekplexia, although eight parents reported jerky leg movements during sleep. The hallmark of hyperekplexia consisted of a hyper-alert gaze and an exaggerated startle with delayed habituation, also elicited by nose tapping and air blowing on the face accompanied by increasing rigidity. Nine severely affected infants, presenting with relentless startles, marked stiffness, violent rhythmic jerks, and breath-holding episodes were treated with oral low doses of clonazepam and completely recovered. Overall, the debilitating symptoms of hyperekplexia gradually resolved in all 39 infants, and their developmental assessment by 2 years of age was within the normal range. Therefore a prompt diagnosis of hyperekplexia during the neonatal period and early infancy, and then treatment if required with benzodiazepines to alleviate the debilitating symptoms, may prevent life-threatening events and enable better feeding and handling. Establishing the diagnosis of such a relatively benign disorder with a favorable developmental outcome may avoid unjustified extensive investigations or unnecessary treatment, suspecting an ominous progressive neurologic disorder.

Hyperekplexia: a treatable neurogenetic disease

Hyperekplexia is primarily an autosomal dominant disease characterized by exaggerated startle reflex and neonatal hypertonia. It can be associated with, if untreated, sudden infant death from apnea or aspiration pneumonia and serious injuries and loss of ambulation from frequent falls. Different mutations in the alpha1 subunit of inhibitory glycine receptor (GLRA1) gene have been identified in many affected families. The most common mutation is Arg271 reported in at least 12 independent families. These mutations uncouple the ligand binding and chloride channel function of inhibitory glycine receptor and result in increased excitability in pontomedullary reticular neurons and abnormal spinal reciprocal inhibition. Three mouse models from spontaneous mutations in GLRA1 and beta subunit of inhibitory glycine receptor (GLRB) genes and two transgenic mouse models are valuable for the study of the pathophysiology and the genotype-phenotype correlation of the disease. The disease caused by mutation in GLRB in mice supports the notion that human hyperekplexia with no detectable mutations in GLRA1 may harbor mutations in GLRB. Clonazepam, a gamma aminobutyric acid (GABA) receptor agonist, is highly effective and is the drug of choice. It enhances the GABA-gated chloride channel function and presumably compensates for the defective glycine-gated chloride channel in hyperekplexia. Recognition of the disease will lead to appropriate treatment and genetic counseling.

Successful treatment of severe infantile hyperekplexia with low-dose clobazam

We report two cases of severe infantile hyperekplexia successfully treated with low-dose clobazam. The first case presented at 6 weeks of age with multiple episodes consisting of difficulty diapering because of stiffness and loud inspiratory noises followed by breath-holding in inspiration. She was diagnosed with hyperekplexia and started on clonazepam 0.05 mg daily. This was discontinued because of excessive sleepiness. The second case presented at 3 weeks of age with episodes of crying that would change in pitch and then abruptly stop, followed by leg and arm extension and stiffening. On occasion, there was cyanosis, and she received mouth-to-mouth resuscitation. She was diagnosed with hyperekplexia at 9 months of age. Both infants were treated with clobazam (0.25 and 0.3 mg/kg/day respectively), resulting in resolution of symptoms with no side effects. During treatment, both had minimal startle response to various stimuli and have now been successfully weaned from clobazam. Low-dose clobazam is effective in the treatment of hyperekplexia and is well tolerated in infants.

Hyperekplexia in neonates

Hyperekplexia (startle disease) is a rare non-epileptic disorder characterised by an exaggerated persistent startle reaction to unexpected auditory, somatosensory and visual stimuli, generalised muscular rigidity, and nocturnal myoclonus. The genetic basis is a mutation usually of the arginine residue 271 leading to neuronal hyperexcitability by impairing glycinergic inhibition. Hyperekplexia is usually familial, most often autosomal dominant with complete penetrance and variable expression. It can present in fetal life as abnormal intrauterine movements, or later at any time from the neonatal period to adulthood. Early manifestations include abnormal responses to unexpected auditory, visual, and somatosensory stimuli such as sustained tonic spasm, exaggerated startle response, and fetal posture with clenched fists and anxious stare. The tonic spasms may mimic generalised tonic seizures, leading to apnoea and death. Consistent generalised flexor spasm in response to tapping of the nasal bridge (without habituation) is the clinical hallmark of hyperekplexia. Electroencephalography may show fast spikes initially during the tonic spasms, followed by slowing of background activity with eventual flattening corresponding to the phase of apnoea bradycardia and cyanosis. Electromyography shows a characteristic almost permanent muscular activity with periods of electrical quietness. Nerve conduction velocity is normal. No specific computed tomography findings have been reported yet. Clonazepam, a gamma aminobutyric acid (GABA) receptor agonist, is the treatment of choice for hypertonia and apnoeic episodes. It, however, may not influence the degree of stiffness significantly. A simple manoeuvre like forced flexion of the head and legs towards the trunk is known to be life saving when prolonged stiffness impedes respiration.

Hyperekplexia: a rare differential of neonatal fits described in a developing country

Hyperekplexia is a rare condition in which there is an exaggerated startle response. We report how a case presented in Papua New Guinea (PNG) and was diagnosed with international support. This is the first reported case in PNG. It is an important diagnosis to make to prevent sudden death and inappropriate treatment. The case illustrates the benefit of having a link with an international specialist and we discuss the importance of communication between developing and industrialized countries.