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Dysfunction of the endoplasmic reticulum (ER) in insulin-producing beta cells results in cell loss and diabetes mellitus. Here we report on five individuals from three different consanguineous families with infancy-onset diabetes mellitus and severe neurodevelopmental delay caused by a homozygous p.(Arg371Ser) mutation in FICD. The FICD gene encodes a bifunctional Fic domain-containing enzyme that regulates the ER Hsp70 chaperone, BiP, via catalysis of two antagonistic reactions: inhibitory AMPylation and stimulatory deAMPylation of BiP. Arg371 is a conserved residue in the Fic domain active site. The FICDR371S mutation partially compromises BiP AMPylation in vitro but eliminates all detectable deAMPylation activity. Overexpression of FICDR371S or knock-in of the mutation at the FICD locus of stressed CHO cells results in inappropriately elevated levels of AMPylated BiP and compromised secretion. These findings, guided by human genetics, highlight the destructive consequences of de-regulated BiP AMPylation and raise the prospect of tuning FICD's antagonistic activities towards therapeutic ends., Supported by a Wellcome Trust Principal Research Fellowship to D.R. (Wellcome 200848/Z/16/Z). A Diabetes UK RD Lawrence fellowship to E.D.F. (Grant number 19_0005971), and a Wellcome Trust Senior Research Fellowship to S.E.F. (105636/Z/14/Z). M.N.W. is in receipt of an Independent Fellowship from the Exeter Diabetes Centre of Excellence funded by Research England’s Expanding Excellence in England (E3) fund

To facilitate early deployment of whole-genome sequencing (WGS) for severely ill children, a standardized pipeline for WGS analysis with timely turnaround and primary care pediatric uptake is needed. We developed a bioinformatics pipeline for comprehensive gene-agnostic trio WGS analysis of children suspected of having an undiagnosed monogenic disease that included detection and interpretation of primary genetic mechanisms of disease, including SNVs/indels, CNVs/SVs, uniparental disomy (UPD), imprinted genes, short tandem repeat expansions, mobile element insertions, SMN1/2 copy number calling, and mitochondrial genome variants. We assessed primary care practitioner experience and competence in a large cohort of 521 families (comprising 90% WGS trios). Children were identified by primary practitioners for recruitment, and we used the UK index of multiple deprivation to confirm lack of patient socio-economic status ascertainment bias. Of the 521 children sequenced, 176 (34%) received molecular diagnoses, with rates as high as 45% for neurology clinics. Twenty-three of the diagnosed cases (13%) required bespoke methods beyond routine SNV/CNV analysis. In our multidisciplinary clinician user experience assessment, both pediatricians and clinical geneticists expressed strong support for rapid WGS early in the care pathway, but requested further training in determining patient selection, consenting, and variant interpretation. Rapid trio WGS provides an efficacious single-pass screening test for children when deployed by primary practitioners in clinical settings that carry high a priori risk for rare pediatric disease presentations.

Mesencephalic astrocyte-derived neurotrophic factor (MANF) is an endoplasmic reticulum (ER)-resident protein that plays a crucial role in attenuating ER stress responses. Although MANF is indispensable for the survival and function of mouse β-cells, its precise role in human β-cell development and function is unknown. In this study, we show that lack of MANF in humans results in diabetes due to increased ER stress, leading to impaired β-cell function. We identified two patients from different families with childhood diabetes and a neurodevelopmental disorder associated with homozygous loss-of-function mutations in the MANF gene. To study the role of MANF in human β-cell development and function, we knocked out the MANF gene in human embryonic stem cells and differentiated them into pancreatic endocrine cells. Loss of MANF induced mild ER stress and impaired insulin-processing capacity of β-cells in vitro. Upon implantation to immunocompromised mice, the MANF knockout grafts presented elevated ER stress and functional failure, particularly in recipients with diabetes. By describing a new form of monogenic neurodevelopmental diabetes syndrome caused by disturbed ER function, we highlight the importance of adequate ER stress regulation for proper human β-cell function and demonstrate the crucial role of MANF in this process. Funding: the genetic studies were funded by Wellcome Trust awarded to Kashyp Patel (grant 110082/Z/15/Z). Kashyp Patel is a Wellcome trust Fellow (grant 219606/Z/19/Z). A.T.H. is a Wellcome Trust Senior Investigator (WT098395/Z/12/Z). The experimental studies were funded by the Academy of Findland (grant 297466 and MetaStem Center of Excellence grant 312437), the Sigrid Jusélius Foundation, the Novo Nordisk Foundation and the JDRF (Grant 2-SRA-2018-496-A-B, PI Mart Saarma, co-PI TO)

Summary Objective Hyperinsulinaemic hypoglycaemia (HH) can occur in isolation or more rarely feature as part of a syndrome. Screening for mutations in the “syndromic” HH genes is guided by phenotype with genetic testing used to confirm the clinical diagnosis. As HH can be the presenting feature of a syndrome, it is possible that mutations will be missed as these genes are not routinely screened in all newly diagnosed individuals. We investigated the frequency of pathogenic variants in syndromic genes in infants with HH who had not been clinically diagnosed with a syndromic disorder at referral for genetic testing. Design We used genome sequencing data to assess the prevalence of mutations in syndromic HH genes in an international cohort of patients with HH of unknown genetic cause. Patients We undertook genome sequencing in 82 infants with HH without a clinical diagnosis of a known syndrome at referral for genetic testing. Measurements Within this cohort, we searched for the genetic aetiologies causing 20 different syndromes where HH had been reported as a feature. Results We identified a pathogenic KMT2D variant in a patient with HH diagnosed at birth, confirming a genetic diagnosis of Kabuki syndrome. Clinical data received following the identification of the mutation highlighted additional features consistent with the genetic diagnosis. Pathogenic variants were not identified in the remainder of the cohort. Conclusions Pathogenic variants in the syndromic HH genes are rare; thus, routine testing of these genes by molecular genetics laboratories is unlikely to be justified in patients without syndromic phenotypes.

Objective Rare genetic disorders resulting in prenatal or neonatal death are genetically heterogeneous, but testing is often limited by the availability of fetal DNA, leaving couples without a potential prenatal test for future pregnancies. We describe our novel strategy of exome sequencing parental DNA samples to diagnose recessive monogenic disorders in an audit of the first 50 couples referred. Method Exome sequencing was carried out in a consecutive series of 50 couples who had 1 or more pregnancies affected with a lethal or prenatal‐onset disorder. In all cases, there was insufficient DNA for exome sequencing of the affected fetus. Heterozygous rare variants (MAF, What's already known about this topic? Exome sequencing is used routinely for postnatal diagnosis of rare disorders with a diagnostic yield of 20 to 40%.Insufficient quantity or quality of DNA restricts the use of exome sequencing for diagnosing lethal fetal disorders.Couples are counselled for a likely 25% recurrence risk, but without a genetic diagnosis, no molecular prenatal test is possible.A parental exome sequencing strategy has been applied successfully in a small number of couples. What does this study add? We show that exome sequencing of parental DNA samples is an effective way to diagnose lethal or prenatal‐onset disorders with a diagnostic yield of 52% in an audit of 50 consecutive cases.Testing can be carried out in the prenatal period to guide management of an ongoing pregnancy or for use in subsequent pregnancies to allow couples the option of a prenatal or preimplantation genetic test.