Variants associated with meconium ileus in cystic fibrosis (CF) were identified in 3,763 patients by GWAS. Five SNPs at two loci near SLC6A14 (min P=1.28×10−12 at rs3788766), chr Xq23-24 and SLC26A9 (min P=9.88×10−9 at rs4077468), chr 1q32.1 accounted for ~5% of the phenotypic variability, and were replicated in an independent patient collection (n=2,372; P=0.001 and 0.0001 respectively). By incorporating that disease-causing mutations in CFTR alter electrolyte and fluid flux across epithelia into an hypothesis-driven genome-wide analysis (GWAS-HD), we identified the same SLC6A14 and SLC26A9 associated SNPs, while establishing evidence for the involvement of SNPs in a third solute carrier gene, SLC9A3. In addition, GWAS-HD provided evidence of association between meconium ileus and multiple constituents of the apical plasma membrane where CFTR resides (P=0.0002, testing 155 apical genes jointly and replicated, P=0.022). These findings suggest that modulating activities of apical membrane constituents could complement current therapeutic paradigms for cystic fibrosis.

Exome sequencing has markedly enhanced the discovery of genes implicated in Mendelian disorders, particularly for individuals in whom a known clinical entity could not be assigned. This has led to the recognition that phenotypic heterogeneity resulting from allelic mutations occurs more commonly than previously appreciated. Here, we report that missense variants in CDC42, a gene encoding a small GTPase functioning as an intracellular signaling node, underlie a clinically heterogeneous group of phenotypes characterized by variable growth dysregulation, facial dysmorphism, and neurodevelopmental, immunological, and hematological anomalies, including a phenotype resembling Noonan syndrome, a developmental disorder caused by dysregulated RAS signaling. In silico, in vitro, and in vivo analyses demonstrate that mutations variably perturb CDC42 function by altering the switch between the active and inactive states of the GTPase and/or affecting CDC42 interaction with effectors, and differentially disturb cellular and developmental processes. These findings reveal the remarkably variable impact that dominantly acting CDC42 mutations have on cell function and development, creating challenges in syndrome definition, and exemplify the importance of functional profiling for syndrome recognition and delineation.

No abstract

Certain mutations can cause proteins to accumulate in neurons, leading to neurodegeneration. We recently showed, however, that upregulation of a wild-type protein, Ataxin1, caused by haploinsufficiency of its repressor, the RNA-binding protein Pumilio1 (PUM1), also causes neurodegeneration in mice. We therefore searched for human patients with PUM1 mutations. We identified eleven individuals with either PUM1 deletions or de novo missense variants who suffer a developmental syndrome (Pumilio1-associated developmental disability, ataxia, and seizure; PADDAS). We also identified a milder missense mutation in a family with adult-onset ataxia with incomplete penetrance (Pumilio1-related cerebellar ataxia, PRCA). Studies in patient-derived cells revealed that the missense mutations reduced PUM1 protein levels by ∼25% in the adult-onset cases and by ∼50% in the infantile-onset cases; levels of known PUM1 targets increased accordingly. Changes in protein levels thus track with phenotypic severity, and identifying posttranscriptional modulators of protein expression should identify new candidate disease genes.

VPS13 protein family members VPS13A through VPS13C have been associated with various recessive movement disorders. We describe the first disease association of rare recessive VPS13D variants including frameshift, missense, and partial duplication mutations with a novel complex, hyperkinetic neurological disorder. The clinical features include developmental delay, a childhood onset movement disorder (chorea, dystonia, or tremor), and progressive spastic ataxia or paraparesis. Characteristic brain magnetic resonance imaging shows basal ganglia or diffuse white matter T2 hyperintensities as seen in Leigh syndrome and choreoacanthocytosis. Muscle biopsy in 1 case showed mitochondrial aggregates and lipidosis, suggesting mitochondrial dysfunction. These findings underline the importance of the VPS13 complex in neurological diseases and a possible role in mitochondrial function. Ann Neurol 2018;83:1089-1095.

Whole exome sequencing (WES) can be used to efficiently identify de novo genetic variants associated with genetically heterogeneous conditions including intellectual disabilities. We have performed WES for 4102 (1847 female; 2255 male) intellectual disability/developmental delay cases and we report five patients with a neurodevelopmental disorder associated with developmental delay, intellectual disability, behavioral problems, hypotonia, speech problems, microcephaly, pachygyria and dysmorphic features in whom we have identified de novo missense and canonical splice site mutations in CSNK2A1, the gene encoding CK2α, the catalytic subunit of protein kinase CK2, a ubiquitous serine/threonine kinase composed of two regulatory (β) and two catalytic (α and/or α') subunits. Somatic mutations in CSNK2A1 have been implicated in various cancers; however, this is the first study to describe a human condition associated with germline mutations in any of the CK2 subunits.

Lung disease is the major cause of morbidity and mortality in cystic fibrosis (CF), an autosomal recessive disease caused by mutations in CFTR. In CF, chronic infection and dysregulated neutrophilic inflammation lead to progressive airway destruction. The severity of CF lung disease has significant heritability, independent of CFTR genotype1. To identify genetic modifiers, we performed a genome-wide single nucleotide polymorphism (SNP) scan in one cohort of CF patients, replicating top candidates in an independent cohort. This approach identified IFRD1 as a modifier of CF lung disease severity. IFRD1 is a histone deacetylase (HDAC)-dependent transcriptional co-regulator expressed during terminal neutrophil differentiation. Neutrophils, but not macrophages, from Ifrd1-deficient mice exhibited blunted effector function, associated with decreased NF-κB p65 transactivation. In vivo, IFRD1 deficiency caused delayed bacterial clearance from the airway, but also less inflammation and disease—a phenotype primarily dependent on hematopoietic cell expression, or lack of expression, of IFRD1. In humans, IFRD1 polymorphisms were significantly associated with variation in neutrophil effector function. These data suggest that IFRD1 modulates the pathogenesis of CF lung disease through regulation of neutrophil effector function.

Protein phosphatase 2A (PP2A) is a heterotrimeric protein serine/threonine phosphatase and is involved in a broad range of cellular processes. PPP2R5D is a regulatory B subunit of PP2A and plays an important role in regulating key neuronal and developmental regulation processes such as PI3K/AKT and GSK3β-mediated cell growth, chromatin remodeling and gene transcriptional regulation. Using WES, we identified four de novo variants in PPP2R5D in a total of seven unrelated individuals with ID and other shared clinical characteristics, including autism spectrum disorder, macrocephaly, hypotonia, seizures and dysmorphic features. Among the four variant, two have been previously reported, and two are novel. All four amino acids are highly conserved among the PP2A subunit family, and all change a negatively charged acidic glutamic acid (E) to a positively charged basic lysine (K), and are predicted to disrupt the PP2A subunits binding and impair the dephosphorylation capacity. Our data provides further support for PPP2R5D as a genetic cause of ID.