Novel Functional Properties of Missense Mutations in the Glycine Receptor β Subunit in Startle Disease

Startle disease is a rare disorder associated with mutations in GLRA1 and GLRB, encoding glycine receptor (GlyR) α1 and β subunits, which enable fast synaptic inhibitory transmission in the spinal cord and brainstem. The GlyR β subunit is important for synaptic localization via interactions with gephyrin and contributes to agonist binding and ion channel conductance. Here, we have studied three GLRB missense mutations, Y252S, S321F, and A455P, identified in startle disease patients. For Y252S in M1 a disrupted stacking interaction with surrounding aromatic residues in M3 and M4 is suggested which is accompanied by an increased EC50 value. By contrast, S321F in M3 might stabilize stacking interactions with aromatic residues in M1 and M4. No significant differences in glycine potency or efficacy were observed for S321F. The A455P variant was not predicted to impact on subunit folding but surprisingly displayed increased maximal currents which were not accompanied by enhanced surface expression, suggesting that A455P is a gain-of-function mutation. All three GlyR β variants are trafficked effectively with the α1 subunit through intracellular compartments and inserted into the cellular membrane. In vivo, the GlyR β subunit is transported together with α1 and the scaffolding protein gephyrin to synaptic sites. The interaction of these proteins was studied using eGFP-gephyrin, forming cytosolic aggregates in non-neuronal cells. eGFP-gephyrin and β subunit co-expression resulted in the recruitment of both wild-type and mutant GlyR β subunits to gephyrin aggregates. However, a significantly lower number of GlyR β aggregates was observed for Y252S, while for mutants S321F and A455P, the area and the perimeter of GlyR β subunit aggregates was increased in comparison to wild-type β. Transfection of hippocampal neurons confirmed differences in GlyR-gephyrin clustering with Y252S and A455P, leading to a significant reduction in GlyR β-positive synapses. Although none of the mutations studied is directly located within the gephyrin-binding motif in the GlyR β M3-M4 loop, we suggest that structural changes within the GlyR β subunit result in differences in GlyR β-gephyrin interactions. Hence, we conclude that loss- or gain-of-function, or alterations in synaptic GlyR clustering may underlie disease pathology in startle disease patients carrying GLRB mutations.

Asip (Agouti-signaling protein) aggression gene regulate auditory processing genes in mice

Covid-19 strategy of lockdown has affected the lives of millions. The strict actions to enclose the epidemic have exposed many households to inner tensions. Domestic violence has been reported to increase during the lockdown. However, the reasons for this phenomenon have not been thoroughly investigated. Melanocortin GPCRs family contribution to aggression is well documented. ASIP (nonagouti) gene plays a vital role in regulating the melanocortin GPCRs family function, and it is responsible for regulating aggression in mice. We conducted a selection analysis of ASIP. We found that it negatively purified from Shark to humans. In order to better asses the effect of this gene in mammals, we performed RNA-seq analysis of a knockout of an ASIP crisper-cas mouse model. We found that ASIP KO in mice upregulates several genes controlling auditory function, including Phox2b, Mpk13, Fat2, Neurod2, Slc18a3, Gon4l Gbx2, Slc6a3(Dat1) Aldh1a7 Tyrp1 and Lbx1. Interestingly, we found that Slc6a5, and Lamp5 as well as IL33, which are associated with startle disease, are also upregulated in response to knocking out ASIP. These findings are indicative of a direct autoimmune effect between aggression-associated genes and startle disease. Furthermore, in order to validate the link between aggression and auditory inputs processing. We conducted psychological tests of persons who experienced lockdown. We found that aggression has risen by 16 % during the lockdown. Furthermore, 3% of the subjects interviewed reported a change in their hearing abilities. Our data shed light on the importance of the auditory input in aggression and open perceptions to interpret how hearing and aggression interact at the molecular neural circuit level.

Hyperekplexia, A Rare Cause of Neonatal Hypertonia: Report of Two Cases

Hyperekplexia (startle disease) is a rare neurogenetic disorder, frequently misdiagnosed with the risk of choking on food, apnea and sudden death. Recognition of this disorder in the neonatal period is essential to avoid erroneous diagnoses and to start early treatment that has proven effective. We report two cases of two newborns who were initially admitted in our neonatal intensive care unit for management of suspected tetanus and epilepsy. Following clinical and paraclinical investigations, a final diagnosis of hyperekplexia was retained in both cases and a low dose of clonazepam was administered. The symptoms gradually decreased until disappearance of hypertonia and startles.

Hyperekplexia in a neonate: a seizure mimicker

Hyperekplexia is an exaggerated startle to external stimuli associated with generalized increase in tone seen in a normal newborn with both sporadic as well as genetic predisposition. This is an uncommon neurological entity that is often confused with seizure in infancy. To date about 150 cases have been reported in the literature. We report a 6-week-old infant with characteristic intermittent generalized tonic spasm misdiagnosed as seizure disorder and was on phenobarbitone. With characteristic stiffening episode and exaggerated startle without habituation on tapping the nose we came to a clinical diagnosis of Hyperekplexia or Stiff baby syndrome or Startle disease. The child was started on Clonazepam to which he responded remarkably with decreased startle reflex. The aim of this case reporting is to through insight to this disease entity when we see an intermittent hypertonic infant.