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Nuclear receptor corepressor 1 (NCOR1) and NCOR2 (also known as SMRT) regulate gene expression by activating histone deacetylase 3 through their deacetylase activation domain (DAD). We show that mice with DAD knock-in mutations have memory deficits, reduced anxiety levels, and reduced social interactions. Mice with NCOR1 and NORC2 depletion specifically in GABAergic neurons (NS-V mice) recapitulated the memory deficits and had reduced GABAA receptor subunit α2 (GABRA2) expression in lateral hypothalamus GABAergic (LHGABA) neurons. This was associated with LHGABA neuron hyperexcitability and impaired hippocampal long-term potentiation, through a monosynaptic LHGABA to CA3GABA projection. Optogenetic activation of this projection caused memory deficits, whereas targeted manipulation of LHGABA or CA3GABA neuron activity reversed memory deficits in NS-V mice. We describe de novo variants in NCOR1, NCOR2 or HDAC3 in patients with intellectual disability or neurodevelopmental disorders. These findings identify a hypothalamus–hippocampus projection that may link endocrine signals with synaptic plasticity through NCOR-mediated regulation of GABA signaling.Zhou et al. show that NCORs regulate memory and synaptic plasticity through a GABAergic hypothalamus–hippocampus projection in mice, and that variants in NCOR1 and NCOR2 are linked to intellectual disability and neurodevelopmental defects in humans.

The variant spectrum and the phenotype of X-linked Kabuki syndrome type 2 (KS2) are poorly understood. Genetic and clinical details of new and published individuals with pathogenic KDM6A variants were compiled and analyzed. Sixty-one distinct pathogenic KDM6A variants (50 truncating, 11 missense) from 80 patients (34 males, 46 females) were identified. Missense variants clustered in the TRP 2, 3, 7 and Jmj-C domains. Truncating variants were significantly more likely to be de novo. Thirteen individuals had maternally inherited variants and one had a paternally inherited variant. Neonatal feeding difficulties, hypoglycemia, postnatal growth retardation, poor weight gain, motor delay, intellectual disability (ID), microcephaly, congenital heart anomalies, palate defects, renal malformations, strabismus, hearing loss, recurrent infections, hyperinsulinism, seizures, joint hypermobility, and gastroesophageal reflux were frequent clinical findings. Facial features of over a third of patients were not typical for KS. Males were significantly more likely to be born prematurely, have shorter stature, and severe developmental delay/ID. We expand the KDM6A variant spectrum and delineate the KS2 phenotype. We demonstrate that the variability of the KS2 phenotypic depends on sex and the variant type. We also highlight the overlaps and differences between the phenotypes of KS2 and KS1.

We present a case of a 13-year-old boy with abdominal pain initially misdiagnosed as gastrointestinal in origin. Despite initial outpatient management, his symptoms rapidly deteriorated, revealing a central-medullary cavernous malformation causing spinal cord compression. This case underscores the importance of a comprehensive pediatric examination and highlights new treatment approaches for spinal cavernous malformations.

Coenzyme Q (CoQ) is an electron acceptor for sulfide‐quinone reductase (SQR), the first enzyme of the hydrogen sulfide oxidation pathway. Here, we show that lack of CoQ in human skin fibroblasts causes impairment of hydrogen sulfide oxidation, proportional to the residual levels of CoQ. Biochemical and molecular abnormalities are rescued by CoQ supplementation in vitro and recapitulated by pharmacological inhibition of CoQ biosynthesis in skin fibroblasts and ADCK3 depletion in HeLa cells. Kidneys of Pdss2 kd/kd mice, which only have ~15% residual CoQ concentrations and are clinically affected, showed (i) reduced protein levels of SQR and downstream enzymes, (ii) accumulation of hydrogen sulfides, and (iii) glutathione depletion. These abnormalities were not present in brain, which maintains ~30% residual CoQ and is clinically unaffected. In Pdss2 kd/kd mice, we also observed low levels of plasma and urine thiosulfate and increased blood C4‐C6 acylcarnitines. We propose that impairment of the sulfide oxidation pathway induced by decreased levels of CoQ causes accumulation of sulfides and consequent inhibition of short‐chain acyl‐CoA dehydrogenase and glutathione depletion, which contributes to increased oxidative stress and kidney failure. Synopsis Coenzyme Q (CoQ) is an electron acceptor for sulfide‐quinone reductase (SQR), the first enzyme of the hydrogen sulfide oxidation pathway. Lack of CoQ is here shown to cause impairment of hydrogen sulfide oxidation in vitro and in vivo . Reduced levels of CoQ in vitro cause impairment of the hydrogen sulfide oxidation pathway and increased protein persulfhydration levels. Reduced levels of CoQ in vivo impair the sulfide oxidation pathway determining accumulation of sulfides and consequent inhibition of short‐chain acyl‐CoA dehydrogenase. Graphical Abstract Coenzyme Q (CoQ) is an electron acceptor for sulfide‐quinone reductase (SQR), the first enzyme of the hydrogen sulfide oxidation pathway. Lack of CoQ is here shown to cause impairment of hydrogen sulfide oxidation in vitro and in vivo .

Background/Objectives: Triosephosphate Isomerase (TPI) is a glycolytic enzyme known to be associated with TPI deficiency, a severe form of childhood-onset glycolytic enzymopathy associated with hemolytic anemia, neuromuscular impairment and early death. Most often the disease results from the common TPI1E105D mutation, which can be either homozygous or compound heterozygous with another allele. Methods: We purified TPIR5G protein, studied mutant protein biochemistry, established and characterized TPIR5G/f.s.patient cells, and investigated newly identified compounds for their efficacy in vitro using Western blot and TPI activity assays. Results: We identified novel TPI1 alleles that result in TPI Deficiency with an atypical presentation lacking anemia and with more slowly developing neurologic and locomotor impairment. The patient was found to be compound heterozygous with a missense mutation resulting in an R5G amino acid substitution and a frameshift mutation that is a predicted null allele. To better understand disease pathogenesis in this patient, we expressed and purified the TPIR5G human protein and studied it biochemically in addition to studying TPIR5G/f.s.patient cells. We discovered that purified TPIR5G protein has wildtype activity with modestly increased dimer stability. We also discovered that steady-state TPI protein levels were markedly reduced, suggesting that the instability of the mutant protein underlies disease pathogenesis. We tested compounds recently identified in a screen for novel TPI Df therapies for their efficacy in TPIR5G/f.s.patient cells. All three compounds significantly increased TPI protein levels in patient cells. As expected, since the mutant protein retains essentially wild type activity, the increase in TPI protein levels also resulted in a significant increase in TPI activity. Conclusions: These results establish TPIR5G as a TPI Df allele, demonstrate that reduced stability of the mutant protein underlies pathogenesis akin to other disease-causing alleles, and suggest that recently discovered developing therapies will likely function broadly and should be developed as potential TPI Df therapies.

Glycine receptors (GlyRs) containing the α2 subunit govern cell fate, neuronal migration and synaptogenesis in the developing cortex and spinal cord. Rare missense variants and microdeletions in the X-linked GlyR α2 subunit gene ( GLRA2 ) have been associated with human autism spectrum disorder (ASD), where they typically cause a loss-of-function via protein truncation, reduced cell-surface trafficking and/or reduced glycine sensitivity (e.g., GLRA2 Δex8-9 and extracellular domain variants p.N109S and p.R126Q). However, the GlyR α2 missense variant p.R323L in the intracellular M3-M4 domain results in a gain-of-function characterized by slower synaptic decay times, longer duration active periods and increases in channel conductance. This study reports the functional characterization of four missense variants in GLRA2 associated with ASD or developmental disorders (p.V-22L, p.N38K, p.K213E, p.T269M) using a combination of bioinformatics, molecular dynamics simulations, cellular models of GlyR trafficking and electrophysiology in artificial synapses. The GlyR α2 V–22L variant resulted in altered predicted signal peptide cleavage and a reduction in cell-surface expression, suggestive of a partial loss-of-function . Similarly, GlyR α2 N38K homomers showed reduced cell-surface expression, a reduced affinity for glycine and a reduced magnitude of IPSCs in artificial synapses. By contrast, GlyR α2 K213E homomers showed a slight reduction in cell-surface expression, but IPSCs were larger, with faster rise/decay times, suggesting a gain-of-function . Lastly, GlyR α2 T269M homomers exhibited a high glycine sensitivity accompanied by a substantial leak current, suggestive of an altered function that could dramatically enhance glycinergic signaling. These results may explain the heterogeneity of clinical phenotypes associated with GLRA2 mutations and reveal that missense variants can result in a loss, gain or alteration of GlyR α2 function. In turn, these GlyR α2 missense variants are likely to either negatively or positively deregulate cortical progenitor homeostasis and neuronal migration in the developing brain, leading to changes in cognition, learning, and memory.

Intracellular cobalamin metabolism (ICM) defects can be present as autosomal recessive or X‐linked disorders. Parenteral hydroxocobalamin (P‐OHCbl) is the mainstay of therapy, but the optimal dose has not been determined. Despite early treatment, long‐term complications may develop. We have analyzed the biochemical and clinical responses in five patients with early onset of different types of ICM defects (cblC: patients 1‐3; cblA: patient 4; cblX: patient 5) following daily P‐OHCbl dose intensification (DI). In patient 4, P‐OHCbl was started at age 10 years and in patient 5 at age 5 years. OHCbl was formulated at either, 5, 25, or 50 mg/mL. P‐OHCbl was intravenously or subcutaneously (SQ) delivered, subsequently by placement of a SQ injection port except in patient 4. In all patients, homocysteine and methylmalonic acid levels, demonstrated an excellent response to various P‐OHCbl doses. After age 36 months, patients 1‐3 had a close to normal neurological examination with lower range developmental quotient. In patient 3, moderate visual impairment was present. Patient 4, at age 10 years, had normal renal, visual and cognitive function. In cblX patient 5, epilepsy was better controlled. In conclusion, P‐OHCbl‐DI caused an excellent control of metabolites in all patients. In the three cblC patients, comparison with patients, usually harboring identical genotype and similar metabolic profile, was suggestive of a positive effect, in favor of clinical efficacy. With P‐OHCbl‐DI, CblA patient has been placed into a lower risk to develop renal and optic impairment. In cblX patient, lower P‐OHCbl doses were administrated to improve tolerability.

Adrenal insufficiency (AI) in a newborn due to hypothalamic–pituitary–adrenal (HPA) axis suppression after maternal glucocorticoid therapy during pregnancy is a rare condition. We report an AI triggered by a nosocomial infection in a premature newborn. The suspected mechanism was the suppression of the HPA axis due to high doses of maternal glucocorticoid treatment during pregnancy. AI was revealed by recurrent hypoglycaemia and mild hyponatraemia during the neonatal period. His twin brother did not develop AI, showing the variable sensitivity of adrenal suppression after exposure to the same glucocorticoid dose. The affected boy was substituted with hydrocortisone until the age of 2 years. At this age, basal morning values for cortisol and Adrenocorticotropic hormone (ACTH) had normalised. The patient also suffers from galactosaemia. We suggest screening for AI, by testing for hypoglycaemia and hyponatraemia, in newborns who were exposed to high doses of maternal methylprednisolone treatment during the pregnancy and to include galactosaemia in national neonatal screening programmes.

Tubulinopathies are a heterogeneous group of conditions with a wide spectrum of clinical severity resulting from variants in genes of the tubulin superfamily. Variants in TUBG1 have been described in three patients with posterior predominant pachygyria and microcephaly. We here report eight additional patients with four novel heterozygous variants in TUBG1 identified by next-generation sequencing (NGS) analysis. All had severe motor and cognitive impairment and all except one developed seizures in early life. The core imaging features included a pachygyric cortex with posterior to anterior gradient, enlarged lateral ventricles most pronounced over the posterior horns, and variable degrees of reduced white matter volume. Basal ganglia, corpus callosum, brainstem, and cerebellum were often normal, in contrast to patients with variants in other tubulin genes where these structures are frequently malformed. The imaging phenotype associated with variants in TUBG1 is therefore more in line with the phenotype resulting from variants in LIS1 (a.k.a. PAFAH1B1). This difference may, at least in part, be explained by gamma-tubulin’s physiological function in microtubule nucleation, which differs from that of alpha and beta-tubulin.

Triosephosphate Isomerase (TPI) is a glycolytic enzyme known to be associated with TPI deficiency, a severe form of childhood-onset glycolytic enzymopathy associated with hemolytic anemia, neuromuscular impairment and early death. Most often the disease results from the common mutation, which can be either homozygous or compound heterozygous with another allele. We purified protein, studied mutant protein biochemistry, established and characterized patient cells, and investigated newly identified compounds for their efficacy in vitro using Western blot and TPI activity assays. We identified novel alleles that result in TPI Deficiency with an atypical presentation lacking anemia and with more slowly developing neurologic and locomotor impairment. The patient was found to be compound heterozygous with a missense mutation resulting in an R5G amino acid substitution and a frameshift mutation that is a predicted null allele. To better understand disease pathogenesis in this patient, we expressed and purified the TPI human protein and studied it biochemically in addition to studying patient cells. We discovered that purified TPI protein has wildtype activity with modestly increased dimer stability. We also discovered that steady-state TPI protein levels were markedly reduced, suggesting that the instability of the mutant protein underlies disease pathogenesis. We tested compounds recently identified in a screen for novel TPI Df therapies for their efficacy in patient cells. All three compounds significantly increased TPI protein levels in patient cells. As expected, since the mutant protein retains essentially wild type activity, the increase in TPI protein levels also resulted in a significant increase in TPI activity. These results establish as a TPI Df allele, demonstrate that reduced stability of the mutant protein underlies pathogenesis akin to other disease-causing alleles, and suggest that recently discovered developing therapies will likely function broadly and should be developed as potential TPI Df therapies.