Clustered de novo start-loss variants in GLUL result in a developmental and epileptic encephalopathy via stabilization of glutamine synthetase.

Glutamine synthetase (GS), encoded by GLUL, catalyzes the conversion of glutamate to glutamine. GS is pivotal for the generation of the neurotransmitters glutamate and gamma-aminobutyric acid and is the primary mechanism of ammonia detoxification in the brain. GS levels are regulated post-translationally by an N-terminal degron that enables the ubiquitin-mediated degradation of GS in a glutamine-induced manner. GS deficiency in humans is known to lead to neurological defects and death in infancy, yet how dysregulation of the degron-mediated control of GS levels might affect neurodevelopment is unknown. We ascertained nine individuals with severe developmental delay, seizures, and white matter abnormalities but normal plasma and cerebrospinal fluid biochemistry with de novo variants in GLUL. Seven out of nine were start-loss variants and two out of nine disrupted 5' UTR splicing resulting in splice exclusion of the initiation codon. Using transfection-based expression systems and mass spectrometry, these variants were shown to lead to translation initiation of GS from methionine 18, downstream of the N-terminal degron motif, resulting in a protein that is stable and enzymatically competent but insensitive to negative feedback by glutamine. Analysis of human single-cell transcriptomes demonstrated that GLUL is widely expressed in neuro- and glial-progenitor cells and mature astrocytes but not in post-mitotic neurons. One individual with a start-loss GLUL variant demonstrated periventricular nodular heterotopia, a neuronal migration disorder, yet overexpression of stabilized GS in mice using in utero electroporation demonstrated no migratory deficits. These findings underline the importance of tight regulation of glutamine metabolism during neurodevelopment in humans.

De novo missense variants in exon 9 of SEPHS1 cause a neurodevelopmental condition with developmental delay, poor growth, hypotonia, and dysmorphic features.

Selenophosphate synthetase (SEPHS) plays an essential role in selenium metabolism. Two mammalian SEPHS paralogues, SEPHS1 and SEPHS2, share high sequence identity and structural homology with SEPHS. Here, we report nine individuals from eight families with developmental delay, growth and feeding problems, hypotonia, and dysmorphic features, all with heterozygous missense variants in SEPHS1. Eight of these individuals had a recurrent variant at amino acid position 371 of SEPHS1 (p.Arg371Trp, p.Arg371Gln, and p.Arg371Gly); seven of these variants were known to be de novo. Structural modeling and biochemical assays were used to understand the effect of these variants on SEPHS1 function. We found that a variant at residue Trp352 results in local structural changes of the C-terminal region of SEPHS1 that decrease the overall thermal stability of the enzyme. In contrast, variants of a solvent-exposed residue Arg371 do not impact enzyme stability and folding but could modulate direct protein-protein interactions of SEPSH1 with cellular factors in promoting cell proliferation and development. In neuronal SH-SY5Y cells, we assessed the impact of SEPHS1 variants on cell proliferation and ROS production and investigated the mRNA expression levels of genes encoding stress-related selenoproteins. Our findings provided evidence that the identified SEPHS1 variants enhance cell proliferation by modulating ROS homeostasis. Our study supports the hypothesis that SEPHS1 plays a critical role during human development and provides a basis for further investigation into the molecular mechanisms employed by SEPHS1. Furthermore, our data suggest that variants in SEPHS1 are associated with a neurodevelopmental disorder.

PIGO-CDG: A case study with a new genotype, expansion of the phenotype, literature review, and nosological considerations.

The phosphatidylinositol glycan anchor biosynthesis class O protein (PIGO) enzyme is an important step in the biosynthesis of glycosylphosphatidylinositol (GPI), which is essential for the membrane anchoring of several proteins. Bi-allelic pathogenic variants in PIGO lead to a congenital disorder of glycosylation (CDG) characterized by global developmental delay, an increase in serum alkaline phosphatase levels, congenital anomalies including anorectal, genitourinary, and limb malformations in most patients; this phenotype has been alternately called "Mabry syndrome" or "hyperphosphatasia with impaired intellectual development syndrome 2." We report a 22-month-old female with PIGO deficiency caused by novel PIGO variants. In addition to the Mabry syndrome phenotype, our patient's clinical picture was complicated by intermittent hypoglycemia with signs of functional hyperinsulinism, severe secretory diarrhea, and osteopenia with a pathological fracture, thus, potentially expanding the known phenotype of this disorder, although more studies are necessary to confirm these associations. We also provide an updated review of the literature, and propose unifying the nomenclature of PIGO deficiency as "PIGO-CDG," which reflects its pathophysiology and position in the broad scope of metabolic disorders and congenital disorders of glycosylation.

Efficacy and safety of a synthetic biotic for treatment of phenylketonuria: a phase 2 clinical trial.

Despite available treatment options, many patients with phenylketonuria (PKU) cannot achieve target plasma phenylalanine (Phe) levels1. We previously modified Escherichia coli Nissle 1917 to metabolize Phe in the gut after oral administration (SYNB1618) and designed a second strain (SYNB1934) with enhanced activity of phenylalanine ammonia lyase2,3. In a 14-day open-label dose-escalation study (Synpheny-1, NCT04534842 ), we test a primary endpoint of change from baseline in labeled Phe (D5-Phe AUC0-24; D5-Phe area under the curve (AUC) over 24 hours after D5-Phe administration) in plasma after D5-Phe challenge in adult participants with screening Phe of greater than 600 µM. Secondary endpoints were the change from baseline in fasting plasma Phe and the incidence of treatment-emergent adverse events. A total of 20 participants (ten male and ten female) were enrolled and 15 completed the study treatment. Here, we show that both strains lower Phe levels in participants with PKU: D5-Phe AUC0-24 was reduced by 43% from baseline with SYNB1934 and by 34% from baseline with SYNB1618. SYNB1934 led to a decrease in fasting plasma Phe of 40% (95% CI, -52, -24). There were no serious adverse events or infections. Four participants discontinued because of adverse events, and one withdrew during the baseline period. We show that synthetic biotics can metabolize Phe in the gut, lower post-prandial plasma Phe levels and lower fasting plasma Phe in patients with PKU.

Biochemical characterization of patients with dihydrolipoamide dehydrogenase deficiency.

Dihydrolipoamide dehydrogenase (DLD; E3) oxidizes lipoic acid. Restoring the oxidized state allows lipoic acid to act as a necessary electron sink for the four mitochondrial keto-acid dehydrogenases: pyruvate dehydrogenase, alpha-ketoglutarate dehydrogenase, branched-chain α-keto-acid dehydrogenase, and 2-oxoadipate dehydrogenase. DLD deficiency (DLDD) is caused by biallelic pathogenic variants in DLD. Three major forms have been described: encephalopathic, hepatic, and myopathic, although DLDD patients exhibit overlapping phenotypes. Hyperlactatemia, hyperexcretion of tricarboxylic acid cycle (TCA) metabolites and branched-chain keto acids, increased plasma branched-chain amino acids and allo-isoleucine are intermittent metabolic abnormalities reported in patients with DLDD. However, the diagnostic performance of these metabolites has never been studied. Therefore, we sought to systematically evaluate the diagnostic utility of these biomarkers for DLDD. We retrospectively analyzed the results of biochemical testing of six unrelated DLDD patients, including values obtained during both well visits and acute decompensation episodes. Elevation of branched-chain amino acid concentrations was not consistently observed. We found that five of six patients in our cohort had a maximum lifetime value of allo-isoleucine of 6 µmol/L, showing that alloisoleucine elevations even during illness may be subtle. Urine organic acid analysis (UOA) during acute decompensation episodes was abnormal in all cases; however, the pattern of abnormalities had high intersubject variability. No single biomarker was universally present, even in patients experiencing metabolic decompensation. We also observed novel biochemical associations: three patients had hyperexcretion of TCA cycle metabolites during crisis; in two patients, 2-ketoadipic and 2-hydroxyadipic acids, by products of lysine degradation, were detected. We propose that these result from 2-oxoadipate dehydrogenase deficiency, an underappreciated biochemical abnormality in DLD. Given the diversity of biochemical profiles among the patients with DLDD, we conclude that accurate biochemical diagnosis relies on a high index of suspicion and multipronged biochemical analysis, including both plasma amino acid and urine organic acid quantitation during decompensation. Biochemical diagnosis during the well state is challenging. We emphasize the critical importance of multiple simultaneous biochemical tests for diagnosis and monitoring of DLDD. We also highlight the under-recognized role of DLD in the lysine degradation pathway. Larger cohorts of patients are needed to establish a correlation between the biochemical pattern and clinical outcomes, as well as a genotype-phenotype correlation.

Rapid Characterization of the Functional and Pharmacological Consequences of Cantú Syndrome KATP Channel Mutations in Intact Cells.

Gain-of-function of KATP channels, resulting from mutations in either KCNJ8 (encoding inward rectifier sub-family 6 [Kir6.1]) or ABCC9 (encoding sulphonylurea receptor [SUR2]), cause Cantú syndrome (CS), a channelopathy characterized by excess hair growth, coarse facial appearance, cardiomegaly, and lymphedema. Here, we established a pipeline for rapid analysis of CS mutation consequences in Landing pad HEK 293 cell lines stably expressing wild type (WT) and mutant human Kir6.1 and SUR2B. Thallium-influx and cell membrane potential, reported by fluorescent Tl-sensitive Fluozin-2 and voltage-sensitive bis-(1,3-dibutylbarbituric acid)trimethine oxonol (DiBAC4(3)) dyes, respectively, were used to assess channel activity. In the Tl-influx assay, CS-associated Kir6.1 mutations increased sensitivity to the ATP-sensitive potassium (KATP) channel activator, pinacidil, but there was strikingly little effect of pinacidil for any SUR2B mutations, reflecting unexpected differences in the molecular mechanisms of Kir6.1 versus SUR2B mutations. Compared with the Tl-influx assay, the DiBAC4(3) assay presents more significant signal changes in response to subtle KATP channel activity changes, and all CS mutants (both Kir6.1 and SUR2B), but not WT channels, caused marked hyperpolarization, demonstrating that all mutants were activated under ambient conditions in intact cells. Most SUR2 CS mutations were markedly inhibited by <100 nM glibenclamide, but sensitivity to inhibition by glibenclamide, repaglinide, and PNU37883A was markedly reduced for Kir6.1 CS mutations. Understanding functional consequences of mutations can help with disease diagnosis and treatment. The analysis pipeline we have developed has the potential to rapidly identify mutational consequences, aiding future CS diagnosis, drug discovery, and individualization of treatment. SIGNIFICANCE STATEMENT: We have developed new fluorescence-based assays of channel activities and drug sensitivities of Cantú syndrome (CS) mutations in human Kir6.1/SUR2B-dependent KATP channels, showing that Kir6.1 mutations increase sensitivity to potassium channel openers, while SUR2B mutations markedly reduce K channel opener (KCO) sensitivity. However, both Kir6.1 and SUR2B CS mutations are both more hyperpolarized than WT cells under basal conditions, confirming pathophysiologically relevant gain-of-function, validating DiBAC4(3) fluorescence to characterize hyperpolarization induced by KATP channel activity under basal, non KCO-activated conditions.

Postmortem diagnosis of very long chain acyl-CoA dehydrogenase (VLCAD) deficiency in a neonate with sudden cardiac death.

Very long chain acyl-CoA dehydrogenase (VLCAD) deficiency is an autosomal recessive long chain fatty acid ß-oxidation disorder with a variable clinical spectrum, ranging from an acute neonatal presentation with cardiac and hepatic failure to childhood or adult onset of symptoms with hepatomegaly or rhabdomyolysis provoked by illness or exertion. Neonatal cardiac arrest or sudden unexpected death can be the presenting phenotype in some patients, emphasizing the importance of early clinical suspicion and intervention. We report a patient who had a cardiac arrest and died at one day of age. Following her death, the newborn screen reported biochemical evidence of VLCAD deficiency, which was confirmed with pathologic findings at autopsy and by molecular genetic testing.

Electrophysiology of human iPSC-derived vascular smooth muscle cells and cell autonomous consequences of Cantu Syndrome mutations.

Objective: Cantu Syndrome (CS), a multisystem disease with a complex cardiovascular phenotype, is caused by GoF variants in the Kir6.1/SUR2 subunits of ATP-sensitive potassium (K ATP ) channels, and is characterized by low systemic vascular resistance, as well as tortuous, dilated vessels, and decreased pulse-wave velocity. Thus, CS vascular dysfunction is multifactorial, with distinct hypomyotonic and hyperelastic components. To dissect whether such complexities arise cell-autonomously within vascular smooth muscle cells (VSMCs), or as secondary responses to the pathophysiological milieu, we assessed electrical properties and gene expression in human induced pluripotent stem cell-derived VSMCs (hiPSC-VSMCs), differentiated from control and CS patient-derived hiPSCs, and in native mouse control and CS VSMCs. Approach and Results: Whole-cell voltage-clamp of isolated aortic and mesenteric VSMCs isolated from wild type (WT) and Kir6.1[V65M] (CS) mice revealed no difference in voltage-gated K + (K v ) or Ca 2+ currents. K v and Ca 2+ currents were also not different between validated hiPSC-VSMCs differentiated from control and CS patient-derived hiPSCs. Pinacidil-sensitive K ATP currents in control hiPSC-VSMCs were consistent with those in WT mouse VSMCs, and were considerably larger in CS hiPSC-VSMCs. Consistent with lack of any compensatory modulation of other currents, this resulted in membrane hyperpolarization, explaining the hypomyotonic basis of CS vasculopathy. Increased compliance and dilation in isolated CS mouse aortae, was associated with increased elastin mRNA expression. This was consistent with higher levels of elastin mRNA in CS hiPSC-VSMCs, suggesting that the hyperelastic component of CS vasculopathy is a cell-autonomous consequence of vascular K ATP GoF. Conclusions: The results show that hiPSC-VSMCs reiterate expression of the same major ion currents as primary VSMCs, validating the use of these cells to study vascular disease. The results further indicate that both the hypomyotonic and hyperelastic components of CS vasculopathy are cell-autonomous phenomena driven by K ATP overactivity within VSMCs.

Effects of TP63 mutations on keratinocyte adhesion and migration.

The goal of this study was to investigate the molecular mechanisms responsible for the formation of skin erosions in patients affected by Ankyloblepharon-ectodermal defects-cleft lip/palate syndrome (AEC). This ectodermal dysplasia is caused by mutations in the TP63 gene, which encodes several transcription factors that control epidermal development and homeostasis. We generated induced pluripotent stem cells (iPSC) from AEC patients and corrected the TP63 mutations using genome editing tools. Three pairs of the resulting conisogenic iPSC lines were differentiated into keratinocytes (iPSC-K). We identified a significant downregulation of key components of hemidesmosomes and focal adhesions in AEC iPSC-K compared to their gene-corrected counterparts. Further, we demonstrated reduced AEC iPSC-K migration, suggesting the possibility that a process critical for cutaneous wound healing might be impaired in AEC patients. Next, we generated chimeric mice expressing a TP63-AEC transgene and confirmed a downregulation of these genes in transgene-expressing cells in vivo. Finally, we also observed these abnormalities in AEC patient skin. Our findings suggest that integrin defects in AEC patients might weaken the adhesion of keratinocytes to the basement membrane. We propose that reduced expression of extracellular matrix adhesion receptors, potentially in conjunction with previously identified desmosomal protein defects, contribute to skin erosions in AEC.

Clinical, neuroradiological, and molecular characterization of mitochondrial threonyl-tRNA-synthetase (TARS2)-related disorder.

PURPOSE: Biallelic variants in TARS2, encoding the mitochondrial threonyl-tRNA-synthetase, have been reported in a small group of individuals displaying a neurodevelopmental phenotype but with limited neuroradiological data and insufficient evidence for causality of the variants. METHODS: Exome or genome sequencing was carried out in 15 families. Clinical and neuroradiological evaluation was performed for all affected individuals, including review of 10 previously reported individuals. The pathogenicity of TARS2 variants was evaluated using in vitro assays and a zebrafish model. RESULTS: We report 18 new individuals harboring biallelic TARS2 variants. Phenotypically, these individuals show developmental delay/intellectual disability, regression, cerebellar and cerebral atrophy, basal ganglia signal alterations, hypotonia, cerebellar signs, and increased blood lactate. In vitro studies showed that variants within the TARS2301-381 region had decreased binding to Rag GTPases, likely impairing mTORC1 activity. The zebrafish model recapitulated key features of the human phenotype and unraveled dysregulation of downstream targets of mTORC1 signaling. Functional testing of the variants confirmed the pathogenicity in a zebrafish model. CONCLUSION: We define the clinico-radiological spectrum of TARS2-related mitochondrial disease, unveil the likely involvement of the mTORC1 signaling pathway as a distinct molecular mechanism, and establish a TARS2 zebrafish model as an important tool to study variant pathogenicity.

Jansen-de Vries syndrome: Expansion of the PPM1D clinical and phenotypic spectrum in 34 families.

Jansen-de Vries syndrome (JdVS) is a neurodevelopmental condition attributed to pathogenic variants in Exons 5 and 6 of PPM1D. As the full phenotypic spectrum and natural history remain to be defined, we describe a large cohort of children and adults with JdVS. This is a retrospective cohort study of 37 individuals from 34 families with disease-causing variants in PPM1D leading to JdVS. Clinical data were provided by treating physicians and/or families. Of the 37 individuals, 27 were male and 10 female, with median age 8.75 years (range 8 months to 62 years). Four families document autosomal dominant transmission, and 32/34 probands were diagnosed via exome sequencing. The facial gestalt, including a broad forehead and broad mouth with a thin and tented upper lip, was most recognizable between 18 and 48 months of age. Common manifestations included global developmental delay (35/36, 97%), hypotonia (25/34, 74%), short stature (14/33, 42%), constipation (22/31, 71%), and cyclic vomiting (6/35, 17%). Distinctive personality traits include a hypersocial affect (21/31, 68%) and moderate-to-severe anxiety (18/28, 64%). In conclusion, JdVS is a clinically recognizable neurodevelopmental syndrome with a characteristic personality and distinctive facial features. The association of pathogenic variants in PPM1D with cyclic vomiting bears not only medical attention but also further pathogenic and mechanistic evaluation.

Abrogation of MAP4K4 protein function causes congenital anomalies in humans and zebrafish.

We report 21 families displaying neurodevelopmental differences and multiple congenital anomalies while bearing a series of rare variants in mitogen-activated protein kinase kinase kinase kinase 4 (MAP4K4). MAP4K4 has been implicated in many signaling pathways including c-Jun N-terminal and RAS kinases and is currently under investigation as a druggable target for multiple disorders. Using several zebrafish models, we demonstrate that these human variants are either loss-of-function or dominant-negative alleles and show that decreasing Map4k4 activity causes developmental defects. Furthermore, MAP4K4 can restrain hyperactive RAS signaling in early embryonic stages. Together, our data demonstrate that MAP4K4 negatively regulates RAS signaling in the early embryo and that variants identified in affected humans abrogate its function, establishing MAP4K4 as a causal locus for individuals with syndromic neurodevelopmental differences.

Effects of TP63 Mutations on Keratinocyte Adhesion and Migration.

The goal of this study was to investigate the molecular mechanisms responsible for the formation of skin erosions in patients affected by Ankyloblepharon-ectodermal defects-cleft lip/palate syndrome (AEC). This ectodermal dysplasia is caused by mutations in the TP63 gene, which encodes several transcription factors that control epidermal development and homeostasis. We generated induced pluripotent stem cells (iPSC) from AEC patients and corrected the TP63 mutations using genome editing tools. Three pairs of the resulting conisogenic iPSC lines were differentiated into keratinocytes (iPSC-K). We identified a significant downregulation of key components of hemidesmosomes and focal adhesions in AEC iPSC-K compared to their gene-corrected counterparts. Further, we demonstrated reduced iPSC-K migration, suggesting the possibility that a process critical for cutaneous wound healing might be impaired in AEC patients. Next, we generated chimeric mice expressing a TP63-AEC transgene and confirmed a downregulation of these genes in transgene-expressing cells in vivo. Finally, we also observed these abnormalities in AEC patient skin. Our findings suggest that integrin defects in AEC patients might weaken the adhesion of keratinocytes to the basement membrane. We propose that reduced expression of extracellular matrix adhesion receptors, potentially in conjunction with previously identified desmosomal protein defects, contribute to skin erosions in AEC.

Newborn screening for mucopolysaccharidosis type II: Lessons learned.

We describe our experience with population-based newborn screening for mucopolysaccharidosis type II (MPS II) in 586,323 infants by measurement of iduronate-2-sulfatase activity in dried blood spots between December 12, 2017 and April 30, 2022. A total of 76 infants were referred for diagnostic testing, 0.01% of the screened population. Of these, eight cases of MPS II were diagnosed for an incidence of 1 in 73,290. At least four of the eight cases detected had an attenuated phenotype. In addition, cascade testing revealed a diagnosis in four extended family members. Fifty-three cases of pseudodeficiency were also identified, for an incidence of 1 in 11,062. Our data suggest that MPS II may be more common than previously recognized with a higher prevalence of attenuated cases.

TELO2-related syndrome (You-Hoover-Fong syndrome): Description of 14 new affected individuals and review of the literature.

You-Hoover-Fong syndrome (YHFS) is an autosomal recessive condition caused by pathogenic variants in the TELO2 gene. Affected individuals were reported to have global developmental delay, intellectual disability, microcephaly, dysmorphic facial features, ocular involvement including cortical visual impairment, strabismus, cataract and rotatory nystagmus, movement disorder, hypertonia and spasticity, balance disturbance and ataxia, and abnormal sleep pattern. Other features reported include poor growth, cleft palate, cardiac malformations, epilepsy, scoliosis, and hearing loss. To date, 12 individuals with YHFS have been reported in the literature. Here we describe 14 new individuals with YHFS from 10 families. Their clinical presentation provides additional support of the phenotype recognized previously and delineates the clinical spectrum associated with YHFS syndrome. In addition, we present a review of the literature including follow-up data on four previously reported individuals with YHFS.

Novel LIAS variants in a patient with epilepsy and profound developmental disabilities.

Multiple mitochondrial enzymes employ lipoic acid as a coenzyme. Pathogenic variants in LIAS, encoding lipoic acid synthase (LIAS), are associated with autosomal recessive LIAS-related disorder (OMIM# 614462). This disorder is characterized by infantile-onset hypotonia, profound psychomotor delay, epileptic encephalopathy, nonketotic hyperglycinemia, and lactic acidosis. We present the case of a 20-year-old female who experienced developmental deficits at the age of 6 months and began to have seizures at 3 years of age. Exome sequencing revealed compound heterozygous novel variants in LIAS, designated c.277delC (p.Leu93Ter) and c.542A > T (p.Asp181Val). The p.Leu93Ter variant is predicted to cause loss of function due to the severe truncation of the encoded protein. To examine the p.Asp181Val variant, functional analysis was performed using Baker's yeast (Saccharomyces cerevisiae) lacking LIP5, the homologue of human LIAS. Wild-type LIAS promoted oxidative growth of the lip5∆ yeast strain. In contrast, lip5∆ yeast expressing p.Asp181Val exhibited poor growth, similar to known pathogenic variants, p.Asp215Glu and p.Met310Thr. Our work has expanded the phenotypic and genotypic spectrum of LIAS-related disorder and established the use of the yeast model as a system for functional study of novel missense variants in LIAS.

Protocol for the Phase 2 EDELIFE Trial Investigating the Efficacy and Safety of Intra-Amniotic ER004 Administration to Male Subjects with X-Linked Hypohidrotic Ectodermal Dysplasia.

X-linked hypohidrotic ectodermal dysplasia (XLHED) is a rare genetic disorder characte-rised by abnormal development of the skin and its appendages, such as hair and sweat glands, the teeth, and mucous glands of the airways, resulting in serious, sometimes life-threatening complications like hyperthermia or recurrent respiratory infections. It is caused by pathogenic variants of the ectodysplasin A gene (EDA). Most affected males are hemizygous for EDA null mutations that lead to the absence or inactivity of the signalling protein ectodysplasin A1 (EDA1) and, thus, to the full-blown phenotype with inability to perspire and few if any teeth. There are currently no long-term treatment options for XLHED. ER004 represents a first-in-class protein replacement molecule designed for specific, high-affinity binding to the endogenous EDA1 receptor (EDAR). Its proposed mechanism of action is the replacement of missing EDA1 in yet unborn patients with XLHED. Once bound to EDAR, ER004 activates the EDA/NFκB signalling pathway, which triggers the transcription of genes involved in the normal development of multiple tissues. Following preclinical studies, named-patient use cases demonstrated significant potential of ER004 in affected males treated in utero during the late second and third trimesters of pregnancy. In order to confirm these results, we started the EDELIFE trial, a prospective, open-label, genotype-match controlled, multicentre clinical study to investigate the efficacy and safety of intra-amniotic ER004 administration as a prenatal treatment for male subjects with XLHED. This article summarises the rationale, the study protocol, ethical issues of the trial, and potential pitfalls.

A Unique High-Output Cardiac Hypertrophy Phenotype Arising From Low Systemic Vascular Resistance in Cantu Syndrome.

Background Cardiomegaly caused by left ventricular hypertrophy is a risk factor for development of congestive heart failure, classically associated with decreased systolic and/or diastolic ventricular function. Less attention has been given to the phenotype of left ventricular hypertrophy with enhanced ventricular function and increased cardiac output, which is potentially associated with high-output heart failure. Lack of recognition may pose diagnostic ambiguity and management complexities. Methods and Results We sought to systematically characterize high-output cardiac hypertrophy in subjects with Cantu syndrome (CS), caused by gain-of-function variants in ABCC9, which encodes cardiovascular KATP (ATP-sensitive potassium) channel subunits. We studied the cardiovascular phenotype longitudinally in 31 subjects with CS with confirmed ABCC9 variants (median [interquartile range] age 8 years [3-32 years], body mass index 19.9 [16.5-22.9], 16 male subjects). Subjects with CS presented with significant left ventricular hypertrophy (left ventricular mass index 86.7 [57.7-103.0] g/m2 in CS, n=30; 26.6 [24.1-32.8] g/m2 in controls, n=17; P<0.0001) and low blood pressure (systolic 94.5 [90-103] mm Hg in CS, n=17; 109 [98-115] mm Hg in controls, n=17; P=0.0301; diastolic 60 [56-66] mm Hg in CS, n=17; 69 [65-72] mm Hg in control, n=17; P=0.0063). Most (21/31) subjects with CS exhibited eccentric hypertrophy with normal left ventricular wall thickness. Congestive heart failure symptoms were evident in 4 of the 5 subjects with CS aged >40 years on long-term follow-up. Conclusions The data define the natural history of high-output cardiac hypertrophy resulting from decreased systemic vascular resistance in subjects with CS, a defining population for long-term consequences of high-output hypertrophy caused by low systemic vascular resistance, and the potential for progression to high-output heart failure.

SLITRK2 variants associated with neurodevelopmental disorders impair excitatory synaptic function and cognition in mice.

SLITRK2 is a single-pass transmembrane protein expressed at postsynaptic neurons that regulates neurite outgrowth and excitatory synapse maintenance. In the present study, we report on rare variants (one nonsense and six missense variants) in SLITRK2 on the X chromosome identified by exome sequencing in individuals with neurodevelopmental disorders. Functional studies showed that some variants displayed impaired membrane transport and impaired excitatory synapse-promoting effects. Strikingly, these variations abolished the ability of SLITRK2 wild-type to reduce the levels of the receptor tyrosine kinase TrkB in neurons. Moreover, Slitrk2 conditional knockout mice exhibited impaired long-term memory and abnormal gait, recapitulating a subset of clinical features of patients with SLITRK2 variants. Furthermore, impaired excitatory synapse maintenance induced by hippocampal CA1-specific cKO of Slitrk2 caused abnormalities in spatial reference memory. Collectively, these data suggest that SLITRK2 is involved in X-linked neurodevelopmental disorders that are caused by perturbation of diverse facets of SLITRK2 function.