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OBJECTIVE: To explore the clinical and genetic characteristics of three children with Hyperekplexia.
METHODS: Three children who were diagnosed with Hyperekplexia at the Third Affiliated Hospital of Zhengzhou University between June 2018 and March 2020 were selected as the study subjects. Clinical data of the three children were collected. All children were subjected to whole exome sequencing. Pathogenicity of candidate variants were verified by Sanger sequencing and bioinformatic analysis.
RESULTS: The three children were all males, and had presented exaggerated startle reflexes and generalized stiffness in response to unexpected auditory or tactile stimulation, or had frequent traumatic falls following exaggerated startle. All children had shown positive nose-tapping reflex, though EEG and cranial MRI exams were all negative. Whole exome sequencing revealed that two children had harbored homozygous variants of the GLRB gene, of which the c.1017_c.1018insAG (p.G340Rfs*14) was unreported previously. The third child had harbored compound heterozygous variants of the GLRA1 gene, among which the c.1262T>A (p.IIe421Asn) variant showed an unreported autosomal recessive inheritance. All children had responded well to clonazepam treatment.
CONCLUSIONS: Patients with Hyperekplexia have typical clinical manifestations. Early clinical identification and genetic analysis can facilitate their diagnosis.

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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 is a rare neuronal disorder characterized by an exaggerated startle response to sudden tactile or acoustic stimuli. In this study, we present a Miniature Australian Shepherd family showing clinical signs, which have genetic and phenotypic similarities with human hereditary hyperekplexia: episodes of muscle stiffness that could occasionally be triggered by acoustic stimuli. Whole genome sequence data analysis of two affected dogs revealed a 36-bp deletion spanning the exon-intron boundary in the glycine receptor alpha 1 (GLRA1) gene. Further validation in pedigree samples and an additional cohort of 127 Miniature Australian Shepherds, 45 Miniature American Shepherds and 74 Australian Shepherds demonstrated complete segregation of the variant with the disease, according to an autosomal recessive inheritance pattern. The protein encoded by GLRA1 is a subunit of the glycine receptor, which mediates postsynaptic inhibition in the brain stem and spinal cord. The canine GLRA1 deletion is located in the signal peptide and is predicted to cause exon skipping and subsequent premature stop codon resulting in a significant defect in glycine signaling. Variants in GLRA1 are known to cause hereditary hyperekplexia in humans; however, this is the first study to associate a variant in canine GLRA1 with the disorder, establishing a spontaneous large animal disease model for the human condition.

Paradoxical pseudomyotonia has previously been described in the English Cocker Spaniel (ECS) and English Springer Spaniel (ESS) breeds, without the identification of potentially causative variants. This disease is characterised by episodes of exercise-induced generalised myotonic-like muscle stiffness, phenotypically similar to congenital pseudomyotonia in cattle, and paramyotonia congenita and Brody disease in people. Four additional affected ESS dogs with paradoxical pseudomyotonia are described in this report, together with the identification of the autosomal recessive c.126C>A(p.(Cys42Ter)) SLC7A10 nonsense variant as candidate disease-causing variant in both ECS and ESS. The variant has an estimated prevalence of 2.5% in both breeds in the British study samples, but was not identified in the Belgian study samples. Genetic testing-based breeding should be a useful tool to eliminate this disease in the future, although an effective treatment option is available for severely affected dogs.

BRAT1 encephalopathy is an ultra-rare autosomal recessive neonatal encephalopathy. We delineate the neonatal electroclinical phenotype at presentation and provide insights for early diagnosis.
Through a multinational collaborative, we studied a cohort of neonates with encephalopathy associated with biallelic pathogenic variants in BRAT1 for whom detailed clinical, neurophysiologic, and neuroimaging information was available from the onset of symptoms. Neuropathologic changes were also analyzed.
We included 19 neonates. Most neonates were born at term (16/19) from nonconsanguineous parents. 15/19 (79%) were admitted soon after birth to a neonatal intensive care unit, exhibiting multifocal myoclonus, both spontaneous and exacerbated by stimulation. 7/19 (37%) had arthrogryposis at birth, and all except 1 progressively developed hypertonia in the first week of life. Multifocal myoclonus, which was present in all but 1 infant, was the most prominent manifestation and did not show any EEG correlate in 16/19 (84%). Video-EEG at onset was unremarkable in 14/19 (74%) infants, and 6 (33%) had initially been misdiagnosed with hyperekplexia. Multifocal seizures were observed at a median age of 14 days (range: 1-29). During the first months of life, all infants developed progressive encephalopathy, acquired microcephaly, prolonged bouts of apnea, and bradycardia, leading to cardiac arrest and death at a median age of 3.5 months (range: 20 days to 30 months). Only 7 infants (37%) received a definite diagnosis before death, at a median age of 34 days (range: 25-126), and almost two-thirds (12/19, 63%) were diagnosed 8 days to 12 years postmortem (median: 6.5 years). Neuropathology examination, performed in 3 patients, revealed severely delayed myelination and diffuse astrogliosis, sparing the upper cortical layers.
BRAT1 encephalopathy is a neonatal-onset, rapidly progressive neurologic disorder. Neonates are often misdiagnosed as having hyperekplexia, and many die undiagnosed. The key phenotypic features are multifocal myoclonus, an organized EEG, progressive, persistent, and diffuse hypertonia, and an evolution into refractory multifocal seizures, prolonged bouts of apnea, bradycardia, and early death. Early recognition of BRAT1 encephalopathy allows for prompt workup, appropriate management, and genetic counseling.

Hyperekplexia is a disease that progresses with excessive startle attacks and is included in the differential diagnosis of epilepsy and many movement disorders.
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.
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.
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.