Céline Helsmoortel

Summary: We investigated the interaction between osmotic stress and auxin signaling in leaf growth regulation. Therefore, we grew Arabidopsis thaliana seedlings on agar media supplemented with mannitol to impose osmotic stress and 1‐naphthaleneacetic acid (NAA), a synthetic auxin. We performed kinematic analysis and flow‐cytometry to quantify the effects on cell division and expansion in the first leaf pair, determined the effects on auxin homeostasis and response (DR5::β‐glucuronidase), performed a next‐generation sequencing transcriptome analysis and investigated the response of auxin‐related mutants. Mannitol inhibited cell division and expansion. NAA increased the effect of mannitol on cell division, but ameliorated its effect on expansion. In proliferating cells, NAA and mannitol increased free IAA concentrations at the cost of conjugated IAA and stimulated DR5 promotor activity. Transcriptome analysis shows a large overlap between NAA and osmotic stress‐induced changes, including upregulation of auxin synthesis, conjugation, transport and TRANSPORT INHIBITOR RESPONSE1 (TIR1) and AUXIN RESPONSE FACTOR (ARF) response genes, but downregulation of Aux/IAA response inhibitors. Consistently, arf7/19 double mutant lack the growth response to auxin and show a significantly reduced sensitivity to osmotic stress. Our results show that osmotic stress inhibits cell division during leaf growth of A. thaliana at least partly by inducing the auxin transcriptional response.

Whole genome sequencing of a severely affected dizygotic twin with an autism spectrum disorder and intellectual disability revealed a compound heterozygous mutation in the HTR7 gene as the only variation not detected in control databases. Each parent carries one allele of the mutation, which is not present in an unaffected stepsister. The HTR7 gene encodes the 5-HT7 serotonin receptor that is involved in brain development, synaptic transmission, and plasticity. The paternally inherited p.W60C variant is situated at an evolutionary conserved nucleotide and predicted damaging by Polyphen2. A mutation akin to the maternally inherited pV286I mutation has been reported to significantly affect the binding characteristics of the receptor. Therefore, the observed sequence alterations provide a first suggestive link between a genetic abnormality in the HTR7 gene and a neurodevelopmental disorder. © 2016 Wiley Periodicals, Inc.

Intellectual disability (ID), characterized by an intellectual performance of at least 2 SD (standard deviations) below average is a frequent, lifelong disorder with a prevalence of 2–3%. Today, only for at most half of patients a diagnosis is made. Knowing the cause of the ID is important for patients and their relatives, as it allows for appropriate medical care, prognosis on further development of the disorder, familial counselling or access to support groups. Whole‐exome sequencing (WES) now offers the possibility to identify the genetic cause for patients for which all previously available genetic tests, including karyotyping, specific gene analysis, or microarray analysis did not reveal causative abnormalities. However, data analysis of WES experiments is challenging. Here we present an analysis workflow implementable in any laboratory, requiring no bioinformatics knowledge. We demonstrated its feasibility on a cohort of 10 patients, in which we found a conclusive diagnosis in 3 and a likely diagnosis in 2 more patients. Of the three conclusive diagnoses, one was a clinically suspected mutation missed by Sanger sequencing, and one was an atypical presentation of a known monogenic disorder, highlighting two essential strengths of WES‐based diagnostics.

Mutations inADNPwere recently identified as a frequent cause of syndromic autism, characterized by deficits in social communication and interaction and restricted, repetitive behavioral patterns. Based on its functional domains,ADNPis a presumed transcription factor. The gene interacts closely with the SWI/SNF complex by direct and experimentally verified binding of its C‐terminus to three of its core components. A detailed and systematic clinical assessment of the symptoms observed in our patients allows a detailed comparison with the symptoms observed in other SWI/SNF disorders. While the mutational mechanism of the first 10 patients identified suggested a gain of function mechanism, an 11th patient reported here is predicted haploinsufficient. The latter observation may raise hope for therapy, as addition of NAP, a neuroprotective octapeptide named after the first three amino acids of the sequence NAPVSPIQ, has been reported by others to ameliorate some of the cognitive abnormalities observed in a knockout mouse model. It is concluded that detailed clinical and molecular studies on larger cohorts of patients are necessary to establish a better insight in the genotype phenotype correlation and in the mutational mechanism.

Frank Kooy, Nathalie Van der Aa and colleagues report that de novo mutations in ADNP cause a syndrome characterized by autism, intellectual disability and facial dysmorphisms. ADNP encodes a transcription factor that interacts with components of the SWI/SNF chromatin remodeling complex. Despite the high heritability of autism spectrum disorders (ASD), characterized by persistent deficits in social communication and interaction and restricted, repetitive patterns of behavior, interests or activities1, a genetic diagnosis can be established in only a minority of patients. Known genetic causes include chromosomal aberrations, such as the duplication of the 15q11-13 region, and monogenic causes, as in Rett and fragile-X syndromes. The genetic heterogeneity within ASD is striking, with even the most frequent causes responsible for only 1% of cases at the most. Even with the recent developments in next-generation sequencing, for the large majority of cases no molecular diagnosis can be established2,3,4,5,6,7. Here, we report ten patients with ASD and other shared clinical characteristics, including intellectual disability and facial dysmorphisms caused by a mutation in ADNP, a transcription factor involved in the SWI/SNF remodeling complex. We estimate this gene to be mutated in at least 0.17% of ASD cases, making it one of the most frequent ASD-associated genes known to date.

AnkyrinG, encoded by the ANK3 gene, is involved in neuronal development and signaling. It has previously been implicated in bipolar disorder and schizophrenia by association studies. Most recently, de novo missense mutations in this gene were identified in autistic patients. However, the causative nature of these mutations remained controversial. Here, we report inactivating mutations in the Ankyrin 3 (ANK3) gene in patients with severe cognitive deficits. In a patient with a borderline intelligence, severe attention deficit hyperactivity disorder (ADHD), autism and sleeping problems, all isoforms of the ANK3 gene, were disrupted by a balanced translocation. Furthermore, in a consanguineous family with moderate intellectual disability (ID), an ADHD-like phenotype and behavioral problems, we identified a homozygous truncating frameshift mutation in the longest isoform of the same gene, which represents the first reported familial mutation in the ANK3 gene. The causality of ANK3 mutations in the two families and the role of the gene in cognitive function were supported by memory defects in a Drosophila knockdown model. Thus we demonstrated that ANK3 plays a role in intellectual functioning. In addition, our findings support the suggested association of ANK3 with various neuropsychiatric disorders and illustrate the genetic and molecular relation between a wide range of neurodevelopmental disorders.