Neonatal Hypertonia Research Articles

Hereditary hyperekplexia caused by novel mutations of GLRA1 in Turkish families

Hyperekplexia, also known as startle disease or stiff-person syndrome, is a neurological condition characterized by neonatal hypertonia and a highly exaggerated startle reflex. Genetic studies have linked mutations in the gene encoding glycine receptor alpha1 (GLRA1) with hereditary hyperekplexia. We analyzed four Turkish families with a history of hyperekplexia. Genomic DNA was obtained from members of these families, and the entire coding sequence of GLRA1 was amplified by PCR followed by the sequencing of PCR products. DNA sequences were analyzed by direct observation using an electropherogram and compared with a published reference sequence. We identified three novel mutations in GLRA1. These included a large deletion removing the first 7 of 9 exons, a single-base deletion in exon 8 that results in protein truncation immediately after the deletion, and a missense mutation in exon 7 causing a tryptophan-to-cysteine change in the first transmembrane domain (M1). These mutant alleles have some distinct features as compared to previously identified GLRA1 mutations. Our data provides further evidence for mutational heterogeneity in GLRA1. The new mutant alleles reported here should advance our understanding of the etiology of hyperekplexia.

Familial Hyperekplexia and Refractory Status Epilepticus: A New Autosomal Recessive Syndrome

Hyperekplexia is a rare disorder characterized by an exaggerated startle response to noise and handling and by neonatal hypertonia. It is predominantly an autosomal dominant disease; however, atypical cases with additional variable manifestations have been reported. We report a hitherto undescribed association of hyperekplexia and refractory status epilepticus in two siblings. Both children were born after an uneventful pregnancy to healthy unrelated Ashkenazi Jews. Both had increased startle and tone from birth and later became hypotonic. A metabolic evaluation, including a muscle biopsy, was normal. At the age of 18 months and 12 months, respectively, they developed status epilepticus refractory to all treatment that culminated in death. An autopsy in the girl did not reveal any brain pathology. The unusual association of hyperekplexia and refractory status epilepticus in both children suggests that this is a new autosomal recessive syndrome, possibly a channelopathy affecting both the brain and the spinal cord.

A mutation (V260M) in the middle of the M2 pore-lining domain of the glycine receptor causes hereditary hyperekplexia.

We investigated the molecular basis of hyperekplexia (STHE), an inherited neurological disorder characterised by neonatal hypertonia and an exaggerated startle response, in a kindred and identified a novel missense mutation in the pore-lining M2 domain of the alpha1 subunit of the glycine receptor (GLRA1). Sequencing analysis of all exons of the GLRA1 gene revealed a G1158A base transition in affected, heterozygous patients. The base transition results in a valine to methionine substitution at codon 260 in the middle of the M2 transmembrane domain. The location within the M2 domain suggests for this substitution a likely role in altering ion channel properties.

Hyperekplexia: abnormal startle response due to glycine receptor mutations.

Hyperekplexia is a rare but well-delineated clinical syndrome of pathological startle response and neonatal hypertonia. Many cases result from mutations in the alpha 1 subunit of the glycine receptor (GLRA 1). The clinical features, management and recent genetic studies of hyperekplexia are reviewed. Diagnosis of the disorder should not be difficult, if one is aware of the syndrome. The treatment of first choice is with the benzodiazepine drug clonazepam, which often causes a dramatic although incomplete diminution of startle. Both recessive and dominant mutations in GLRA 1 have been found in affected individuals. The study of mouse mutants with startle phenotypes suggests that the remainder of cases may well be due to mutations in the beta subunit of the glycine receptor. Hyperekplexia is the first human disease shown to result from mutations within a neurotransmitter gene. The demonstration of both dominant and recessive inheritance resulting from different mutations in the same gene is of considerable interest, as other neuropsychiatric disorders may result from mutations in ligand-gated ion channels. Mutation analysis of GLRA 1 is also likely to be useful as an aid to genetic counselling and in diagnostic evaluation of neonatal hypertonia.

A missense mutation in the gene encoding the α1 subunit of the inhibitory glycine receptor in the spasmodic mouse

Hereditary hyperekplexia, an autosomal dominant neurologic disorder characterized by an exaggerated startle reflex and neonatal hypertonia, can be caused by mutations in the gene encoding the alpha 1 subunit of the inhibitory glycine receptor (GLRA1). Spasmodic (spd), a recessive neurologic mouse mutant, resembles hyperekplexia phenotypically, and the two disease loci map to homologous chromosomal regions. Here we describe a Glra1 missense mutation in spd that results in reduced agonist sensitivity in glycine receptors expressed in vitro. We conclude that spd is a murine homologue of hyperekplexia and that mutations in GLRA1/Glra1 can produce syndromes with different inheritance patterns.

Neuroaxonal Dystrophy at Birth With Hypertonicity and Basal Ganglia Mineralization

A full-term male infant exhibited rigidity of all extremities with hyperreflexia beginning soon after birth and lasting until his death at age 6 months. Head circumference remained at the 25th to 50th percentile. Distinct sleep-wake cycles and responsiveness to visual, auditory, and tactile stimuli developed. Metabolic studies, skin biopsy, electroencephalography, and electromyography produced normal results. Head computed tomographic and magnetic resonance imaging scans revealed mineralization of the basal ganglia and thalamus. Muscle and nerve biopsy results were consistent with axonal dystrophy. Autopsy showed widespread neuronal loss, with reactive gliosis, marked in the globus pallidus and brainstem reticulate core; spheroids in globus pallidus, nucleus cuneatus, and upper cervical cord; and mineralized neurons in the inner division of globus pallidus and thalamus. Neonatal hypertonia, rapid progression, and mineralization of the basal ganglia are unusual features of neuroaxonal dystrophy exhibited in this case.