Paroxysmal sensory (spinal) attacks without hyperexplexia in a patient with a variant in the GLRA1 gene

Excessive Startle with Novel GLRA1 Mutations in 4 Chinese Patients and a Literature Review of GLRA1-Related Hyperekplexia

Background and Purpose

Hyperekplexia (HPX), a rare neurogenetic disorder, is classically characterized by neonatal hypertonia, exaggerated startle response provoked by the sudden external stimuli and followed by a shortly general stiffness. Glycine receptor alpha 1 (GLRA1) is the major pathogenic gene of the disease. We described the clinical manifestations of genetically confirmed HPX patients and made a literature review of GLRA1-related HPX to improve the early recognition and prompt the management of the disorder.

Methods

Extensive clinical evaluations were analyzed in 4 Chinese HPX patients from two unrelated families. Next generation sequencing was conducted in the probands. Sanger sequence and segregation analysis were applied to confirm the findings.

Results

All four patients including 3 males and 1 female presented with excessive startle reflex, a cautious gait and recurrent falls. Moreover, startle episodes were dramatically improved with the treatment of clonazepam in all cases. Exome sequencing revealed 2 homozygous GLRA1 mutations in the patients. The mutation c.1286T>A p.I429N has been previously reported, while c.754delC p.L252* is novel.

Conclusions

HPX is a treatable disease, and clonazepam is the drug of choice. By studying and reviewing the disorder, we summarized the phenotype, expanded the genotype spectrum, and discussed the possible pathogenic mechanisms to enhance the understanding and recognition of the disease. Early awareness of the disease is crucial to the prompt and proper administration, as well as the genetic counseling.

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.