Clinical features and genetic analysis of two siblings with startle disease in an Italian family: a case report.

BACKGROUND: Hyperekplexia also known as Startle disease is a rare neuromotor hereditary disorder characterized by exaggerated startle responses to unexpected auditory, tactile, and visual stimuli and generalized muscle stiffness, which both gradually subside during the first months of life. Although the diagnosis of Hyperekplexia is based on clinical findings, pathogenic variants in five genes have been reported to cause Hyperekplexia, of which GLRA1 accounts for about 80% of cases. Dominant and recessive mutations have been identified in GLRA1 gene as pathogenic variants in many individuals with the familial form of Hyperekplexia and occasionally in simplex cases. CASE PRESENTATION: In the present study, we describe clinical and genetic features of two Italian siblings, one with the major and one with the minor form of the disease. DNA samples from the probands and their parents were performed by NGS approach and validated by Sanger sequencing. The analysis of the GLRA1 gene revealed, in both probands, compound heterozygous mutations: c.895C > T or p.R299X inherited from the mother and c.587C > A or p.D98E inherited from the father. CONCLUSIONS: Until now, these two identified mutations in GLRA1 have not been reported before as compound mutations. What clearly emerges within our study is the clinical heterogeneity in the same family. In fact, even though in the same pedigree, the affected mother showed only mild startle responses to unexpected noise stimuli, which might be explained by variable expressivity, while the father, showed no clear signs of symptomatology, which might be explained by non-penetrance. Finally, the two brothers have different form of the disease, even if the compound heterozygous mutations in GLRA1 are the same, showing that the same mutation in GLRA1 could have different phenotypic expressions and suggesting an underling mechanism of variable expressivity.

A novel nonsense autosomal dominant mutation in the GLRA1 gene causing hyperekplexia.

We present a family with two members affected by hyperekplexia and two unaffected members. All exons in the glycine receptor alpha 1 subunit gene (GLRA1) were sequenced in all four family members. Our index patient harbored a novel nonsense mutation (p.Trp314*; rs867618642) in the transmembrane domain three of the GLRA1 and a novel missense variant in the NH2-terminal part (p.Val67Met; rs142888296). After development of tolerance for the effective treatment with clobazam a drug holiday led to a sustained restoration of the treatment response.

A novel compound mutation in GLRA1 cause hyperekplexia in a Chinese boy- a case report and review of the literature.

BACKGROUND: The pathogenesis of hereditary hyperekplexia is thought to involve abnormalities in the glycinergic neurotransmission system, the most of mutations reported in GLRA1. This gene encodes the glycine receptor α1 subunit, which has an extracellular domain (ECD) and a transmembrane domain (TMD) with 4 α-helices (TM1-TM4). CASE PRESENTATION: We investigated the genetic cause of hyperekplexia in a Chinese family with one affected member. Whole-exome sequencing of the 5 candidate genes was performed on the proband patient, and direct sequencing was performed to validate and confirm the detected mutation in other family members. We also review and analyse all reported GLRA1 mutations. The proband had a compound heterozygous GLRA1 mutation that comprised 2 novel GLRA1 missense mutations, C.569C > T (p.T190 M) from the mother and C.1270G > A (p.D424N) from the father. SIFT, Polyphen-2 and MutationTaster analysis identified the mutations as disease-causing, but the parents had no signs of hyperekplexia. The p.T190 M mutation is located in the ECD, while p.D424N is located in TM4. CONCLUSIONS: Our findings contribute to a growing list GLRA1 mutations associated with hyperekplexia and provide new insights into correlations between phenotype and GLRA1 mutations. Some recessive mutations can induce hyperekplexia in combination with other recessive GLRA1 mutations. Mutations in the ECD, TM1, TM1-TM2 loop, TM3, TM3-TM4 loop and TM4 are more often recessive and part of a compound mutation, while those in TM2 and the TM2-TM3 loop are more likely to be dominant hereditary mutations.

Distinct phenotypes in zebrafish models of human startle disease.

Startle disease is an inherited neurological disorder that causes affected individuals to suffer noise- or touch-induced non-epileptic seizures, excessive muscle stiffness and neonatal apnea episodes. Mutations known to cause startle disease have been identified in glycine receptor subunit (GLRA1 and GLRB) and glycine transporter (SLC6A5) genes, which serve essential functions at glycinergic synapses. Despite the significant successes in identifying startle disease mutations, many idiopathic cases remain unresolved. Exome sequencing in these individuals will identify new candidate genes. To validate these candidate disease genes, zebrafish is an ideal choice due to rapid knockdown strategies, accessible embryonic stages, and stereotyped behaviors. The only existing zebrafish model of startle disease, bandoneon (beo), harbors point mutations in glrbb (one of two zebrafish orthologs of human GLRB) that cause compromised glycinergic transmission and touch-induced bilateral muscle contractions. In order to further develop zebrafish as a model for startle disease, we sought to identify common phenotypic outcomes of knocking down zebrafish orthologs of two known startle disease genes, GLRA1 and GLRB, using splice site-targeted morpholinos. Although both morphants were expected to result in phenotypes similar to the zebrafish beo mutant, our direct comparison demonstrated that while both glra1 and glrbb morphants exhibited embryonic spasticity, only glrbb morphants exhibited bilateral contractions characteristic of beo mutants. Likewise, zebrafish over-expressing a dominant startle disease mutation (GlyR α1(R271Q)) exhibited spasticity but not bilateral contractions. Since GlyR ßb can interact with GlyR α subunits 2-4 in addition to GlyR α1, loss of the GlyR ßb subunit may produce more severe phenotypes by affecting multiple GlyR subtypes. Indeed, immunohistochemistry of glra1 morphants suggests that in zebrafish, alternate GlyR α subunits can compensate for the loss of the GlyR α1 subunit. To address the potential for interplay among GlyR subunits during development, we quantified the expression time-course for genes known to be critical to glycinergic synapse function. We found that GlyR α2, α3 and α4a are expressed in the correct temporal pattern and could compensate for the loss of the GlyR α1 subunit. Based on our findings, future studies that aim to model candidate startle disease genes in zebrafish should include measures of spasticity and synaptic development.

Hyperekplexia: A Treatable Seizure Mimicker in Infants.

Hyperekplexia (HK) or startle disease is an uncommon, early infantile onset, potentially treatable neurogenetic disorder. It is characterized by an exaggerated startle reflex in response to tactile or acoustic or visual stimuli followed by generalized hypertonia. It is caused by genetic mutations in a number of different genes such as GLRA1, SLC6A5, GLRB, GPHN, and ARHGEF9. HK is frequently misdiagnosed as a form of epilepsy and is advised for prolonged antiseizure medications. Here, we report a two-month-old female child with HK, who was treated for epilepsy. Next-generation sequencing revealed a pathogenic homozygous missense mutation of variant c.1259C>A in exon 9 of the GLRA1 gene that was compatible with the diagnosis of hyperekplexia-1.

Hereditary Hyperekplexia: A New Family and a Systematic Review of GLRA1 Gene-Related Phenotypes.

Hereditary hyperekplexia (HPX) is a genetic neurodevelopmental disorder recently defined by the triad of (1) neonatal hypertonia, (2) excessive startle reflexes, and (3) generalized stiffness following the startle. Defects in GLRA1 are the most common cause of HPX, inherited both in an autosomal dominant and autosomal recessive manner. GLRA1 mutations can also cause milder phenotypes in the startle syndromes spectrum, but the prevalence is uncertain and no clear genotype-phenotype correlation has emerged yet. Moreover, the prevalence of neurodevelopmental outcomes has not been clearly defined. Here we report a new family of patients with a typical HPX phenotype, linked to a novel GLRA1 mutation, inherited with a recessive pattern. We then perform a systematic review of the literature of GLRA1-related HPX, describing the main epidemiological features of 210 patients. We found that GLRA1-related phenotypes do not necessarily fulfill the current criteria for HPX, including also milder and later-onset phenotypes. Among clinical features of the disease, neurodevelopmental issues were reported in a third of the sample; interestingly, we found that these problems, particularly when severe, were more common in homozygous than in heterozygous patients. Additional clinical and preclinical studies are needed to define predictors of adverse neurodevelopmental outcomes and underlying mechanisms.

Four Turkish families with hyperekplexia: A missense mutation and the exon 1-7 deletion in the GLRA1 gene.

BACKGROUND: Hyperekplexia is a disease that progresses with excessive startle attacks and is included in the differential diagnosis of epilepsy and many movement disorders. METHODS: The WES results were validated in available family members by Sanger sequencing, or in the case of deletion, PCR followed by agarose gel electrophoresis was performed. RESULTS: WES analysis revealed the previously reported homozygous c.277C>T p.Arg93Trp variant in the GLRA1 gene (ENST00000455880.2) in Family 1. In all other three families, the previously reported homozygous deletion of exons 1-7 of the GLRA1 gene was identified using CNV analysis based on the WES data. CONCLUSIONS: The homozygous exon1-7 deletion has been described several times in different populations and may be a founder mutation in the Kurdish people in Turkey. The family with Arg93Trp variant stems from the Black Sea region of Turkey where close consanguinity is common. These analyses are important to provide genetic counseling to families and for a better understanding of the pathophysiology of the disease.

Hereditary Hyperekplexia in Saudi Arabia.

BACKGROUND: Hyperekplexia is a rare disorder characterized by exaggerated startle responses to unexpected sensory stimuli, recurrent apneas, and stiffness. Only few studies have been published on this disorder in populations with high rates of consanguinity. METHODS: We retrospectively reviewed Saudi patients with genetically confirmed hereditary hyperekplexia using a standard questionnaire that was sent to nine major referral hospitals in Saudi Arabia. RESULTS: A total of 22 Saudi patients (11 males, 11 females) from 20 unrelated families who had hereditary hyperekplexia were included. Based on molecular studies, they were classified into different subtypes: SLC6A5 variant (12 patients, 54.5%), GLRB variant (seven patients, 31.8%), and GLRA1 variant (three patients, 13.7%). All patients were homozygous for the respective causal variant. The combined carrier frequency of hereditary hyperekplexia for the encountered founder mutations in the Saudi population is 10.9 per 10,000, which translates to a minimum disease burden of 13 patients per 1,000,000. CONCLUSION: Our study provides comprehensive epidemiologic information, prevalence figures, and clinical characteristics of a large cohort of patients with hereditary hyperekplexia.

Weird Laughing in Hyperekplexia: A new phenotype associated with a novel mutation in the GLRA1 gene?

Hyperekplexia (HPX) or startle disease is a rare hereditary neurological disorder characterized by generalized stiffness, excessive startle reflex to unexpected stimuli and a short period of generalized stiffness following the startle response, and can be complicated by umbilical or inguinal hernia, developmental delay and apnea spell. HPX is caused mainly by mutations in the GLRA1 gene, and has a good response to clonazepam. In this short communication we describe an 11-year-old girl with excessive startle reflex, weird laughing and developmental delay since early infancy. She also suffered from infantile spasms and generalized tonic-clonic seizures, and became seizure-free with antiepileptic drugs treatment. However, the weird laughing was still present during the treatment. Her mother also appeared excessive startle reflex during early infancy. A novel mutation in GLRA1 was detected in the girl and her mother. Consequently, she was diagnosed with HPX, and clonazepam was added. The weird laughing was dramatic improved, which hasn't been reported in HPX. This is the first report of weird laughing in a hyperekplexia patient carrying a novel GLRA1 mutation, and expanded the phenotype spectrum of HPX.

[A pedigree of hereditary hyperekplexia].

A 31-year old women presented with excessive startle reflex and frequent falls. Her startle reflex is induced by slight stimuli which are not problematic in most people. Soon after her startle reflex is evoked, generalized muscle stiffness occurs. She becomes rigid and falls down without loss of consciousness. Because she cannot protect herself when she is startled and falls, she has repeatedly bruised her head and face. The pedigree includes her father and two sisters with similar symptoms. Gene analysis revealed GLRA1 mutation, and she was diagnosed with hereditary hyperekplexia (HPX). Symptoms improved with clonazepam 1 mg/day. HPX patients live with severe anxiety about frequent falls and sometimes suffer serious injury, such as cerebral concussion or bone fracture. Although HPX might sometimes be underestimated, accurate diagnosis is very important for effective treatment.

Familial Hyperekplexia, a Potential Cause of Cautious Gait: A New Korean Case and a Systematic Review of Phenotypes

Familial hyperekplexia, also called startle disease, is a rare neurological disorder characterized by excessive startle responses to noise or touch. It can be associated with serious injury from frequent falls, apnea spells, and aspiration pneumonia. Familial hyperekplexia has a heterogeneous genetic background with several identified causative genes; it demonstrates both dominant and recessive inheritance in the α1 subunit of the glycine receptor (GLRA1), the ß subunit of the glycine receptor and the presynaptic sodium and chloride-dependent glycine transporter 2 genes. Clonazepam is an effective medical treatment for hyperekplexia. Here, we report genetically confirmed familial hyperekplexia patients presenting early adult cautious gait. Additionally, we review clinical features, mode of inheritance, ethnicity and the types and locations of mutations of previously reported hyperekplexia cases with a GLRA1 gene mutation.

Inter- and Intra-Subunit Butanol/Isoflurane Sites of Action in the Human Glycine Receptor.

Glycine receptors (GlyRs) mediate inhibitory neurotransmission and are targets for alcohols and anesthetics in brain. GlyR transmembrane (TM) domains contain critical residues for alcohol/anesthetic action: amino acid A288 in TM3 forms crosslinks with TM1 (I229) in the adjacent subunit as well as TM2 (S267) and TM4 (Y406, W407, I409, Y410) in the same subunit. We hypothesized that these residues may participate in intra-subunit and inter-subunit sites of alcohol/anesthetic action. The following double and triple mutants of GLRA1 cDNA (encoding human glycine receptor alpha 1 subunit) were injected into Xenopus laevis oocytes: I229C/A288C, I229C/A288C/C290S, A288C/Y406C, A288C/W407C, A288C/I409C, and A288C/Y410C along with the corresponding single mutants and wild-type GLRA1. Butanol (22 mM) or isoflurane (0.6 mM) potentiation of GlyR-mediated currents before and after application of the cysteine crosslinking agent HgCl2 (10 µM) was measured using two-electrode voltage clamp electrophysiology. Crosslinking nearly abolished butanol and isoflurane potentiation in the I229C/A288C and I229C/A288C/C290S mutants but had no effect in single mutants or wild-type. Crosslinking also inhibited butanol and isoflurane potentiation in the TM3-4 mutants (A288C/Y406C, A288C/W407C, A288C/I409C, A288C/Y410C) with no effect in single mutants or wild-type. We extracted proteins from oocytes expressing I229C/288C, A288C/Y410C, or wild-type GlyRs, used mass spectrometry to verify their expression and possible inter-subunit dimerization, plus immunoblotting to investigate the biochemical features of proposed crosslinks. Wild-type GlyR subunits measured about 50 kDa; after crosslinking, the dimeric/monomeric 100:50 kDa band ratio was significantly increased in I229C/288C but not A288C/Y410C mutants or wild-type, providing support for TM1-3 inter-subunit and TM3-4 intra-subunit crosslinking. A GlyR homology model based on the GluCl template provides further evidence for a multi-site model for alcohol/anesthetic interaction with human GLRA1.

Hyperekplexia: a Chinese adolescent with 2 novel mutations of the GLRA1 gene.

Hyperekplexia is a rare neurologic disorder, characterized by excessive startle response to unexpected stimuli. There are 3 cardinal features: generalized stiffness immediately after birth that normalizes during the first year of life; excessive startle reflex to unexpected (particularly auditory) stimuli; and a short period of generalized stiffness following the startle response while patient cannot elicit voluntary movements. Awareness of this condition will avoid misdiagnosis of disorders like epilepsy. Clonazepam is an effective medical treatment. We report a patient whose frequent falls triggered by sudden noise or tactile stimuli was initially misdiagnosed as epilepsy. The clinical diagnosis was subsequently revised to hyperekplexia and confirmed by mutation analysis of the GLRA1 gene, which showed c.497G>C (p.Cys166Ser) and c.526delG (p.Asp176Metfs*16). Both of them are novel mutations. His response to clonazepam is dramatic and has been able to engage in sports and social activities.

Effect of antipsychotic drugs on gene expression in the prefrontal cortex and nucleus accumbens in the spontaneously hypertensive rat (SHR).

Antipsychotic drugs (APDs) are the standard treatment for schizophrenia. The therapeutic effect of these drugs is dependent upon the dopaminergic D2 blockade, but they also modulate other neurotransmitter pathways. The exact mechanisms underlying the clinical response to APDs are not fully understood. In this study, we compared three groups of animals for the expression of 84 neurotransmitter genes in the prefrontal cortex (PFC) and nucleus accumbens (NAcc). Each group was treated with a different APD (risperidone, clozapine or haloperidol), and with a non-treated group of spontaneously hypertensive rats (SHRs), which is an animal model for schizophrenia. This study also explored whether or not differential expression was regulated by DNA methylation in the promoter region (PR). In the clozapine group, we found that Chrng was downregulated in the NAcc and six genes were downregulated in the PFC. In the haloperidol group, Brs3 and Glra1 were downregulated, as was Drd2 in the clozapine group and Drd3, Galr3 and Gabrr1 in the clozapine and haloperidol groups. We also encountered four hypermethylated CG sites in the Glra1 PR, as well as three in the risperidone group and another in the haloperidol group, when compared to non-treated rats. Following the APD treatment, the gene expression results revealed the involvement of genes that had not previously been described, in addition to the activity of established genes. The investigation of the involvement of these novel genes can lead to better understanding about the specific mechanisms of action of the individual APDs studied.

Glycinergic transmission in the Mammalian retina.

Glycine and gamma-aminobutyric acid (GABA) are the major inhibitory neurotransmitters in the retina. Approximately half of the amacrine cells release glycine at their synapses with bipolar, other amacrine, and ganglion cells. Glycinergic amacrine cells are small-field amacrine cells with vertically oriented dendrites and comprise more than 10 different morphological types. The retinal distributions of glycine receptor (GlyR) alpha1, alpha2, alpha3 and alpha4 subtypes have been mapped with subunit-specific antibodies. GlyRs were clustered at postsynaptic hot spots which showed selective distributions for the different subunits. As a rule, only one alpha subunit was expressed at a given postsynaptic site. The kinetic properties of GlyRs were measured by recording spontaneous inhibitory postsynaptic currents (sIPSCs) from identified retinal neurons in wild-type, Glra1(spd-ot), Glra2 and Glra3 knockout mice. From observed differences of sIPSCs in wild-type and mutant mice, the cell-type specific subunit composition of GlyRs could be defined. OFF-cone bipolar cells and A-type ganglion cells receive prominent glycinergic input with fast kinetics that is mainly mediated by alpha1beta GlyRs (decay time constant tau approximately 5 ms). By contrast, AII amacrine cells express alpha3beta GlyRs with medium fast kinetics (tau approximately 11 ms). Narrow-field (NF) and wide-field amacrine cells contain predominantly alpha2beta GlyRs with slow kinetics (tau approximately 27 ms). Lastly, ON-starburst, narrow-field and wide-field amacrine cells in Glra2 knockout mice express alpha4beta GlyRs with very slow kinetics (tau approximately 70 ms).