A family harboring an MLKL loss of function variant implicates impaired necroptosis in diabetes

Maturity-onset diabetes of the young, MODY, is an autosomal dominant disease with incomplete penetrance. In a family with multiple generations of diabetes and several early onset diabetic siblings, we found the previously reported P33T PDX1 damaging mutation. Interestingly, this substitution was also present in a healthy sibling. In contrast, a second very rare heterozygous damaging mutation in the necroptosis terminal effector, MLKL, was found exclusively in the diabetic family members. Aberrant cell death by necroptosis is a cause of inflammatory diseases and has been widely implicated in human pathologies, but has not yet been attributed functions in diabetes. Here, we report that the MLKL substitution observed in diabetic patients, G316D, results in diminished phosphorylation by its upstream activator, the RIPK3 kinase, and no capacity to reconstitute necroptosis in two distinct MLKL−/− human cell lines. This MLKL mutation may act as a modifier to the P33T PDX1 mutation, and points to a potential role of impairment of necroptosis in diabetes. Our findings highlight the importance of family studies in unraveling MODY’s incomplete penetrance, and provide further support for the involvement of dysregulated necroptosis in human disease.

Characterization of Early-Onset Finger Osteoarthritis-Like Condition Using Patient-Derived Induced Pluripotent Stem Cells

Early osteoarthritis (OA)-like symptoms are difficult to study owing to the lack of disease samples and animal models. In this study, we generated induced pluripotent stem cell (iPSC) lines from a patient with a radiographic early-onset finger osteoarthritis (efOA)-like condition in the distal interphalangeal joint and her healthy sibling. We differentiated those cells with similar genetic backgrounds into chondrogenic pellets (CPs) to confirm efOA. CPs generated from efOA-hiPSCs (efOA-CPs) showed lower levels of COL2A1, which is a key marker of hyaline cartilage after complete differentiation, for 21 days. Increase in pellet size and vacuole-like morphologies within the pellets were observed in the efOA-CPs. To analyze the changes occurred during the development of vacuole-like morphology and the increase in pellet size in efOA-CPs, we analyzed the expression of OA-related markers on day 7 of differentiation and showed an increase in the levels of COL1A1, RUNX2, VEGFA, and AQP1 in efOA-CPs. IL-6, MMP1, and MMP10 levels were also increased in the efOA-CPs. Taken together, we present proof-of-concept regarding disease modeling of a unique patient who showed OA-like symptoms.

QOL-38. USE OF COMPUTERIZED NEUROPSYCHOLOGICAL MEASURES TO ASSESS COGNITIVE MORBIDITY IN SURVIVORS OF CHILDHOOD BRAIN TUMORS

Treatment of central nervous system (CNS) tumors in pediatric populations is associated with significant cognitive morbidity. Documentation of neuropsychological deficits is vital to treatment and educational planning. We investigated the feasibility and utility of a computerized neuropsychological measure (NIH Toolbox Cognitive Battery) in differentiating individuals who received tumor treatment from healthy controls. Participants included pediatric CNS tumor survivors (N = 85; Mean Age = 13.47; SD = 4.76) at least 1-year post-completion of treatment and healthy sibling controls (N = 20; Mean Age = 10.2; SD = 3.21) who completed the NIH Toolbox. Ninety-eight percent of the participants enrolled completed the computerized tasks. The overall logistical regression model, with NIH Toolbox tests as predictors, was statistically significant [χ2 (7, N = 105) = 26.176; p < .001] and improved correct group classification from 81% to 82.9%. Picture Sequencing (β = -0.059; Wald = 6.942; p = .008) and Flanker (β = -0.083; Wald = 7.473; p = .006) were both statistically significant and negatively predictive of membership in the treatment group. For each 1 unit increase in standard score on measures of working memory and inhibition, odds of membership in the treatment group decreased by 6.2% and 8.7%, respectively. Consistent with the literature, worse performance on computerized measures of cognitive functioning mediated by executive functioning was correlated with a history of brain tumor treatment. Further investigation will focus on comparing computerized neuropsychological tools to traditional comprehensive neuropsychological evaluations and clarifying the trajectory of these deficits across recovery.

NCOG-72. DIFFERENTIAL EFFECTS OF SURGERY AND CHEMOTHERAPY ON CHILDREN WITH POSTERIOR FOSSA BRAIN TUMORS

BACKGROUND Few neuroimaging studies of children with brain tumors treated with chemotherapy without radiation exist, and the neuropsychological effects of chemotherapy remain unclear. We aimed to differentiate the effects of surgery and chemotherapy on brain microstructure and cognition. METHODS Twenty-eight children with a history of posterior fossa tumor (17 treated with surgery alone; 11 treated with surgery + chemotherapy), and 21 sibling controls (n= 49) underwent diffusion tensor imaging (DTI) and neuropsychological assessment a mean of 4.5 (surgery group) to 9 years (surgery + chemotherapy group) after treatment. Psychometric measures focused on general intelligence, executive functions, processing speed, learning and memory, and social-emotional functioning. Age at diagnosis and time since diagnosis were covariates in the analyses. Group differences in DTI findings and psychometric scores, and correlations between psychometric scores and DTI results were examined. RESULTS Mean fractional anisotropy (FA) in the prefrontal cortex, white matter tracts, hippocampus, putamen, globus pallidus, thalamus, and pons were significantly (z≥ 2SD) lower in children treated with surgery + chemotherapy compared to those treated with surgery alone. In neuropsychological evaluation, the patient groups differed only in receptive vocabulary (p= 0.05), with children treated with surgery + chemotherapy scoring lower. Both patient groups scored lower than healthy sibling controls on measures of visuoconstructional reasoning (p= 0.02) and delayed visual (p= 0.02) and spatial memory (p= 0.01). Lower FA in the uncinate fasciculus and higher FA in the right thalamus associated with higher scores on general intelligence (p= 0.003, p= 0.002), and higher FA in the right thalamus associated with higher scores on spatial learning (p= 0.01) and memory (p= 0.01) in children treated with surgery + chemotherapy. CONCLUSIONS Chemotherapy is associated with injury to the microstructure of white and gray matter and neuropsychological deficits not seen in children with posterior fossa tumors treated with surgery alone.

Hearing the Voice of a Shadow Child: Healthy Siblings Experience of Cystic Fibrosis and Other Life-Threatening Conditions

Cystic fibrosis (CF) is a chronic, life-threatening disease, similar to other chronic life-disrupting pediatric conditions, and this creates physical and psychosocial problems for parents and the healthy sibling/s of the sick child, who often become sibling carers. It is feared that, despite good intentions, professionals fail to hear the authentic voice of those intimately involved, especially these sibling carers, who can feel they became a “shadow child.” This study is a partnership between an academic and a former CF sibling carer, who wrote a “fairy story” for his children about the Uncle they never knew. It is an effort to hear the “voice of shadow children” who can feel left behind and unseen as families and professionals focus upon their ill sibling.

Lower estimated bone strength and impaired bone microarchitecture in children with type 1 diabetes

IntroductionPatients with type 1 diabetes has an increased risk of fracture. We wished to evaluate estimated bone strength in children and adolescents with type 1 diabetes and assess peripheral bone geometry, volumetric bone mineral density (vBMD) and microarchitecture.Research design and methodsIn a cross-sectional study, high-resolution peripheral quantitative CT (HR-pQCT) was performed of the radius and tibia in 84 children with type 1 diabetes and 55 healthy sibling controls. Estimated bone strength was assessed using a microfinite element analysis solver. Multivariate regression analyses were performed adjusting for age, sex, height and body mass index.ResultsThe median age was 13.0 years in the diabetes group vs 11.5 years in healthy sibling controls. The median (range) diabetes duration was 4.2 (0.4−15.9) years; median (range) latest year Hb1Ac was 7.8 (5.9−11.8) % (61.8 (41−106) mmol/mol). In adjusted analyses, patients with type 1 diabetes had reduced estimated bone strength in both radius, β −390.6 (−621.2 to −159.9) N, p=0.001, and tibia, β −891.9 (−1321 to −462.9) N, p<0.001. In the radius and tibia, children with type 1 diabetes had reduced cortical area, trabecular vBMD, trabecular number and trabecular bone volume fraction and increased trabecular inhomogeneity, adjusted p<0.05 for all. Latest year HbA1c was negatively correlated with bone microarchitecture (radius and tibia), trabecular vBMD and estimated bone strength (tibia).ConclusionChildren with type 1 diabetes had reduced estimated bone strength. This reduced bone strength could partly be explained by reduced trabecular bone mineral density, adverse microarchitecture and reduced cortical area. We also found increasing latest year HbA1c to be associated with several adverse changes in bone parameters. HR-pQCT holds potential to identify early adverse bone changes and to explain the increased fracture risk in young patients with type 1 diabetes.

A Family Case of Congenital Myasthenic Syndrome-22 Induced by Different Combinations of Molecular Causes in Siblings

Congenital myasthenic syndrome-22 (CMS22, OMIM 616224) is a very rare recessive hereditary disorder. At the moment, ten CMS22 patients are described, with the disorder caused by nine different Loss-of-Function mutations and 14 gross deletions in the PREPL gene. The materials for our study were DNA samples of five family members: two patients with myasthenia, their healthy sibling and parents. Clinical exome analysis was carried out for one patient, then the whole family was checked for target variants with Sanger sequencing, quantitative multiplex ligation-dependent probe amplification, and chromosome 2 microsatellite markers study. To determine the functional significance of the splicing variant, we applied the minigene assay. The cause of the proband’s disorder is a compound heterozygous state of two previously non-described pathogenic PREPL variants: a c.1528C>T (p.(Arg510Ter)) nonsense mutation and a c.2094G>T pseudo-missense variant, which, simultaneously with a p.(Lys698Asn) amino acid substitution, affects splicing, leading to exon 14 skipping in mRNA. The second patient’s disorder was caused by a homozygous nonsense c.1528C>T (p.(Arg510Ter)) mutation due to maternal uniparental disomy (UPD) of chromosome 2. In this study, we describe a unique case, in which two siblings with a rare disorder have different pathologic genotypes.