Mono and biallelic variants in HCN2 cause severe neurodevelopmental disorders.

Hyperpolarization activated Cyclic Nucleotide (HCN) gated channels are crucial for various neurophysiological functions, including learning and sensory functions, and their dysfunction are responsible for brain disorders, such as epilepsy. To date, HCN2 variants have only been associated with mild epilepsy and recently, one monoallelic missense variant has been linked to developmental and epileptic encephalopathy. Here, we expand the phenotypic spectrum of HCN2- related disorders by describing twenty-one additional individuals from fifteen unrelated families carrying HCN2 variants. Seventeen individuals had developmental delay/intellectual disability (DD/ID), two had borderline DD/ID, and one had borderline DD. Ten individuals had epilepsy with DD/ID, with median age of onset of 10 months, and one had epilepsy with normal development. Molecular diagnosis identified thirteen different pathogenic HCN2 variants, including eleven missense variants affecting highly conserved amino acids, one frameshift variant, and one in-frame deletion. Seven variants were monoallelic of which five occurred de novo, one was not maternally inherited, one was inherited from a father with mild learning disabilities, and one was of unknown inheritance. The remaining six variants were biallelic, with four homozygous and two compound heterozygous variants. Functional studies using two-electrode voltage-clamp recordings in Xenopus laevis oocytes were performed on three monoallelic variants, p.(Arg324His), p.(Ala363Val), and p.(Met374Leu), and three biallelic variants, p.(Leu377His), p.(Pro493Leu) and p.(Gly587Asp). The p.(Arg324His) variant induced a strong increase of HCN2 conductance, while p.(Ala363Val) and p.(Met374Leu) displayed dominant negative effects, leading to a partial loss of HCN2 channel function. By confocal imaging, we found that the p.(Leu377His), p.(Pro493Leu) and p.(Gly587Asp) pathogenic variants impaired membrane trafficking, resulting in a complete loss of HCN2 elicited currents in Xenopus oocytes. Structural 3D-analysis in depolarized and hyperpolarized states of HCN2 channels, revealed that the pathogenic variants p.(His205Gln), p.(Ser409Leu), p.(Arg324Cys), p.(Asn369Ser) and p.(Gly460Asp) modify molecular interactions altering HCN2 function. Taken together, our data broadens the clinical spectrum associated with HCN2 variants, and disclose that HCN2 is involved in developmental encephalopathy with or without epilepsy.

DHDDS and NUS1: A Converging Pathway and Common Phenotype.

BACKGROUND: Variants in dehydrodolichol diphosphate synthetase (DHDDS) and nuclear undecaprenyl pyrophosphate synthase 1 (NUS1) cause a neurodevelopmental disorder, classically with prominent epilepsy. Recent reports suggest a complex movement disorder and an overlapping phenotype has been postulated due to their combined role in dolichol synthesis. CASES: We describe three patients with heterozygous variants in DHDDS and five with variants affecting NUS1. They bear a remarkably similar phenotype of a movement disorder dominated by multifocal myoclonus. Diagnostic clues include myoclonus exacerbated by action and facial involvement, and slowly progressive or stable, gait ataxia with disproportionately impaired tandem gait. Myoclonus is confirmed with neurophysiology, including EMG of facial muscles. LITERATURE REVIEW: Ninety-eight reports of heterozygous variants in DHDDS, NUS1 and chromosome 6q22.1 structural alterations spanning NUS1, confirm the convergent phenotype of hypotonia at birth, developmental delay, multifocal myoclonus, ataxia, dystonia and later parkinsonism with or without generalized epilepsy. Other features include periodic exacerbations, stereotypies, anxiety, and dysmorphisms. Although their gene products contribute to dolichol biosynthesis, a key step in N-glycosylation, transferrin isoform profiles are typically normal. Imaging is normal or non-specific. CONCLUSIONS: Recognition of their shared phenotype may expedite diagnosis through chromosomal microarray and by including DHDDS/NUS1 in movement disorder gene panels.

Biallelic loss-of-function variants in RABGAP1 cause a novel neurodevelopmental syndrome.

PURPOSE: RABGAP1 is a GTPase-activating protein implicated in a variety of cellular and molecular processes, including mitosis, cell migration, vesicular trafficking, and mTOR signaling. There are no known Mendelian diseases caused by variants in RABGAP1. METHODS: Through GeneMatcher, we identified 5 patients from 3 unrelated families with homozygous variants in the RABGAP1 gene found on exome sequencing. We established lymphoblastoid cells lines derived from an affected individual and her parents and performed RNA sequencing and functional studies. Rabgap1 knockout mice were generated and phenotyped. RESULTS: We report 5 patients presenting with a common constellation of features, including global developmental delay/intellectual disability, microcephaly, bilateral sensorineural hearing loss, and seizures, as well as overlapping dysmorphic features. Neuroimaging revealed common features, including delayed myelination, white matter volume loss, ventriculomegaly, and thinning of the corpus callosum. Functional analysis of patient cells revealed downregulated mTOR signaling and abnormal localization of early endosomes and lysosomes. Rabgap1 knockout mice exhibited several features in common with the patient cohort, including microcephaly, thinning of the corpus callosum, and ventriculomegaly. CONCLUSION: Collectively, our results provide evidence of a novel neurodevelopmental syndrome caused by biallelic loss-of-function variants in RABGAP1.

PPA2-associated sudden cardiac death: extending the clinical and allelic spectrum in 20 new families.

PURPOSE: Biallelic hypomorphic variants in PPA2, encoding the mitochondrial inorganic pyrophosphatase 2 protein, have been recently identified in individuals presenting with sudden cardiac death, occasionally triggered by alcohol intake or a viral infection. Here we report 20 new families harboring PPA2 variants. METHODS: Synthesis of clinical and molecular data concerning 34 individuals harboring five previously reported PPA2 variants and 12 novel variants, 11 of which were functionally characterized. RESULTS: Among the 34 individuals, only 6 remain alive. Twenty-three died before the age of 2 years while five died between 14 and 16 years. Within these 28 cases, 15 died of sudden cardiac arrest and 13 of acute heart failure. One case was diagnosed prenatally with cardiomyopathy. Four teenagers drank alcohol before sudden cardiac arrest. Progressive neurological signs were observed in 2/6 surviving individuals. For 11 variants, recombinant PPA2 enzyme activities were significantly decreased and sensitive to temperature, compared to wild-type PPA2 enzyme activity. CONCLUSION: We expand the clinical and mutational spectrum associated with PPA2 dysfunction. Heart failure and sudden cardiac arrest occur at various ages with inter- and intrafamilial phenotypic variability, and presentation can include progressive neurological disease. Alcohol intake can trigger cardiac arrest and should be strictly avoided.

Liver transplantation in children with inborn errors of metabolism: 30 years experience in NSW, Australia.

BACKGROUND: Inborn errors of metabolism (IEM) are a diverse group of genetic disorders that can result in significant morbidity and sometimes death. Metabolic management can be challenging and burdensome for families. Liver transplantation (LT) is increasingly being considered a treatment option for some IEMs. IEMs are now considered the second most common reason for pediatric LT. AIM: To review the data of all children with an IEM who had LT at The Children's Hospital at Westmead (CHW), NSW, Australia between January 1986 and January 2019. METHODS: Retrospective data collected from the medical records and genetic files included patient demographics, family history, parental consanguinity, method of diagnosis of IEM, hospital and intensive care unit admissions, age at LT, graft type, clinical outcomes and metabolic management pre and post-LT. RESULTS: Twenty-four LT were performed for 21 patients. IEM diagnoses were MSUD (n = 4), UCD (n = 8), OA (n = 6), TYR type I (n = 2) and GSD Ia (n = 1). Three patients had repeat transplants due to complications. Median age at transplant was 6.21 years (MSUD), 0.87 years (UCD), 1.64 years (OA) and 2.2 years (TYR I). Two patients died peri-operatively early in the series, one died 3 months after successful LT due to septicemia. Eighteen LTs have been performed since 2008 in comparison to six LT prior to 2008. Dietary management was liberalized post LT for all patients. CONCLUSIONS: Referral for LT for IEMs has increased over the last 33 years, with the most referrals in the last 10 years. Early LT has resulted in improved clinical outcomes and patient survival.

Short-acting erythropoiesis-stimulating agents for anaemia in predialysis patients.

BACKGROUND: The benefits of erythropoiesis-stimulating agents (ESA) for chronic kidney disease (CKD) patients have been previously demonstrated. However, the efficacy and safety of short-acting epoetins administered at larger doses and reduced frequency as well as of new epoetins and biosimilars remains uncertain. OBJECTIVES: This review aimed to evaluate the benefits and harms of different routes, frequencies and doses of epoetins (epoetin alpha, epoetin beta and other short-acting epoetins) for anaemia in adults and children with CKD not receiving dialysis. SEARCH METHODS: We searched the Cochrane Kidney and Transplant Specialised Register to 12 September 2016 through contact with the Information Specialist using search terms relevant to this review. Studies contained in the Specialised Register are identified through search strategies specifically designed for CENTRAL, MEDLINE, and EMBASE; handsearching conference proceedings; and searching the International Clinical Trials Register (ICTRP) Search Portal and ClinicalTrials.gov. SELECTION CRITERIA: We included randomised control trials (RCTs) comparing different frequencies, routes, doses and types of short-acting ESAs in CKD patients. DATA COLLECTION AND ANALYSIS: Two authors independently assessed study eligibility and four authors assessed risk of bias and extracted data. Results were expressed as risk ratio (RR) or risk differences (RD) with 95% confidence intervals (CI) for dichotomous outcomes. For continuous outcomes the mean difference (MD) with 95% confidence intervals (CI) was used. Statistical analyses were performed using the random-effects model. MAIN RESULTS: We identified 14 RCTs (2616 participants); nine studies were multi-centre and two studies involved children. The risk of bias was high in most studies; only three studies demonstrated adequate random sequence generation and only two studies were at low risk of bias for allocation concealment. Blinding of participants and personnel was at low risk of bias in one study. Blinding of outcome assessment was judged at low risk in 13 studies as the outcome measures were reported as laboratory results and therefore unlikely to be influenced by blinding. Attrition bias was at low risk of bias in eight studies while selective reporting was at low risk in six included studies.Four interventions were compared: epoetin alpha or beta at different frequencies using the same total dose (six studies); epoetin alpha at the same frequency and different total doses (two studies); epoetin alpha administered intravenously versus subcutaneous administration (one study); epoetin alpha or beta versus other epoetins or biosimilars (five studies). One study compared both different frequencies of epoetin alpha at the same total dose and at the same frequency using different total doses.Data from only 7/14 studies could be included in our meta-analyses. There were no significant differences in final haemoglobin (Hb) levels when dosing every two weeks was compared with weekly dosing (4 studies, 785 participants: MD -0.20 g/dL, 95% CI -0.33 to -0.07), when four weekly dosing was compared with two weekly dosing (three studies, 671 participants: MD -0.16 g/dL, 95% CI -0.43 to 0.10) or when different total doses were administered at the same frequency (four weekly administration: one study, 144 participants: MD 0.17 g/dL 95% CI -0.19 to 0.53).Five studies evaluated different interventions. One study compared epoetin theta with epoetin alpha and found no significant differences in Hb levels (288 participants: MD -0.02 g/dL, 95% CI -0.25 to 0.21). One study found significantly higher pain scores with subcutaneous epoetin alpha compared with epoetin beta. Two studies (165 participants) compared epoetin delta with epoetin alpha, with no results available since the pharmaceutical company withdrew epoetin delta for commercial reasons. The fifth study comparing the biosimilar HX575 with epoetin alpha was stopped after patients receiving HX575 subcutaneously developed anti-epoetin antibodies and no results were available.Adverse events were poorly reported in all studies and did not differ significantly within comparisons. Mortality was only detailed adequately in four studies and only one study included quality of life data. AUTHORS' CONCLUSIONS: Epoetin alpha given at higher doses for extended intervals (two or four weekly) is non-inferior to more frequent dosing intervals in maintaining final Hb levels with no significant differences in adverse effects in non-dialysed CKD patients. However the data are of low methodological quality so that differences in efficacy and safety cannot be excluded. Further large, well designed, RCTs with patient-centred outcomes are required to assess the safety and efficacy of large doses of the shorter acting ESAs, including biosimilars of epoetin alpha, administered less frequently compared with more frequent administration of smaller doses in children and adults with CKD not on dialysis.