An Crepel

SCAMP5, NBEA and AMISYN: three candidate genes for autism involved in secretion of large dense-core vesicles

Autism is a neurodevelopmental disorder characterized by impaired social reciprocity, impaired communication and stereotypical behaviors. Despite strong evidence for a genetic basis, few susceptibility genes have been identified. Here, we describe the positional cloning of SCAMP5, CLIC4 and PPCDC as candidate genes for autism, starting from a person with idiopathic, sporadic autism carrying a de novo chromosomal translocation. One of these genes, SCAMP5 is silenced on the derivative chromosome, and encodes a brain-enriched protein involved in membrane trafficking, similar to the previously identified candidate genes NBEA and AMISYN. Gene silencing of Nbea, Amisyn and Scamp5 in mouse beta-TC3 cells resulted in a 2-fold increase in stimulated secretion of large dense-core vesicles (LDCVs), while overexpression suppressed secretion. Moreover, ultrastructural analysis of blood platelets from the patients with haploinsufficieny of one of the three candidate genes, showed morphological abnormalities of dense-core granules, which closely resemble LDCVs. Taken together, this study shows that in three independent patients with autism three different negative regulators of LDCV secretion are affected, respectively, suggesting that in at least a subgroup of patients the regulation of neuronal vesicle trafficking may be involved in the pathogenesis of autism.

DISC1 duplication in two brothers with autism and mild mental retardation

Crepel A, Breckpot J, Fryns J‐P, De la Marche W, Steyaert J, Devriendt K, Peeters H. DISC1 duplication in two brothers with autism and mild mental retardation.

Narrowing the critical deletion region for autism spectrum disorders on 16p11.2.

Narrowing the Critical Deletion Region for Autism Spectrum Disorders on 16p11.2 An Crepel, Jean Steyaert, Wouter De la Marche, Veerle De Wolf, Jean-Pierre Fryns, Ilse Noens, Koen Devriendt, and Hilde Peeters* Center for Human Genetics, Clinical Genetics, K.U.Leuven, Leuven, Belgium Department of Child and Adolescent Psychiatry, UPC-K.U.Leuven, Leuven, Belgium Department of Clinical Genetics, Academic Hospital Maastricht, and Research Institute Growth & Development (GROW), Maastricht University, Maastricht, The Netherlands Center for Parenting, Child Welfare and Disabilities, Department of Educational Sciences, University of Leuven, Leuven, Belgium Psychiatric and Neurodevelopmental Genetics Unit, Massachusetts General Hospital, Boston, Massachusetts

Position effect leading to haploinsufficiency in a mosaic ring chromosome 14 in a boy with autism

We describe an individual with autism and a coloboma of the eye carrying a mosaicism for a ring chromosome consisting of an inverted duplication of proximal chromosome 14. Of interest, the ring formation was associated with silencing of the amisyn gene present in two copies on the ring chromosome and located at 300 kb from the breakpoint. This observation lends further support for a locus for autism on proximal chromosome 14. Moreover, this case suggests that position effects need to be taken into account, when analyzing genotype–phenotype correlations based on chromosomal imbalances.

Platelet defects in congenital variant of Rett syndrome patients with FOXG1 mutations or reduced expression due to a position effect at 14q12

The Forkhead box G1 (FOXG1) gene encodes a transcriptional repressor essential for early development of the telencephalon. Intragenic mutations and gene deletions leading to haploinsufficiency cause the congenital variant of Rett syndrome. We here describe Rett syndrome-like patients, three of them carrying a balanced translocation with breakpoint in the chromosome 14q12 region, and one patient having a 14q12 microdeletion excluding the FOXG1 gene. The hypothesis of long-range FOXG1-regulatory elements in this region was supported by our finding of reduced FOXG1 mRNA and protein levels in platelets and skin fibroblasts from these cases. Given that FOXG1 is not only expressed in brain but also in platelets, we have studied platelet morphology in these patients and two additional patients with FOXG1 mutations. Electron microscopy of their platelets showed some enlarged, rounder platelets with often abnormal alpha, and fewer dense granules. Platelet function studies were possible in one 14q12 translocation patient with a prolonged Ivy bleeding time and a patient with a heterozygous FOXG1 c.1248C>G mutation (p.Tyr416X). Both have a prolonged PFA-100 occlusion time with collagen and epinephrine and reduced aggregation responses to low dose of ADP and epinephrine. Dense granule ATP secretion was normal for strong agonists but absent for epinephrine. In conclusion, our study shows that by using platelets functional evidence of cis-regulatory elements in the 14q12 region result in reduced FOXG1 levels in patients’ platelets having translocations or deletions in that region. These platelet functional abnormalities deserve further investigation regarding a non-transcriptional regulatory role for FOXG1 in these anucleated cells.

Association of CDH11 with non-syndromic ASD.

We report a sporadic patient with Autism Spectrum Disorder (ASD), mild intellectual disability and attention deficit hyperactivity disorder (ADHD) with a de novo partial deletion of CADHERIN 11 (CDH11). The deletion is associated with one of the breakpoints of a de novo complex chromosomal rearrangement 46,XY,t(3;16;5)(q29;q22;q15)inv4(p14;q21)ins(4;5)(q21;q14.3q15). Cadherins are cell adhesion molecules involved in synaptic plasticity. Since genetic evidence points towards a role for cadherins in ASD, we studied the possible contribution of CDH11 to ASD. A case‐control association study for 14 SNP variants in 519 ASD cases and 1,192 controls showed significant overrepresentation of rs7187376C/C genotypes in the patient group [P = 0.0049 (Chi‐square = 7.90 1 df) and O.R. 3.88 C.I. = 1.403–10.733]. There was no association for C/T versus T/T [P = 0.6772 (Chi‐square = 0.17 1 df)] nor was there association at the allelic level [P = 0.4373 (Chi‐square = 0.6 1 df)]. In addition to the association of common variants in CDH11 with ASD, we studied the possible contribution of rare variants by sequencing CDH11 in 247 patients, and found three novel variants in the coding region of CDH1, of which two variants were unlikely to be causal. Targeted CNV screening in these 247 patients did not reveal copy number variation in CDH11. In conclusion, the data provide evidence for the involvement of CDH11 in ASD which is consistent with the association of other cadherins with ASD and neuropsychiatric diseases.

A complex Xp11.22 deletion in a patient with syndromic autism: Exploration of FAM120C as a positional candidate gene for autism

We present a male patient with sporadic Aarskog syndrome, cleft palate, mild intellectual disability, and autism spectrum disorder (ASD). A submicroscopic discontiguous deletion was detected on chromosome Xp11.2 encompassing FGD1, FAM120C, and PHF8. That the deletion encompassed FGD1 (exons 2–8) explains the Aarskog features while the deletion of PHF8 most likely explains the cleft palate and mild intellectual disability. We identify FAM120C as a novel X‐linked candidate gene for autism for two reasons: first, a larger deletion encompassing FAM120C segregates with autism in a previously reported family and second, there is recent evidence that FAM120C interacts with CYFIP1, part of the FMRP (Fragile X Mental Retardation Protein) network. In the current study, resequencing of FAM120C in 87 Belgian male patients with autism spectrum disorder identified no novel mutations. Expression of Fam120c in mouse tissues showed enriched expression in pituitary, cerebellum, cortex, and pancreatic islets of Langerhans. Additionally, we found a cortical expression pattern of Fam120c similar to that of Fmr1. In conclusion, FAM120C is a novel candidate gene for autism spectrum disorder based on genetic evidence and the brain expression pattern. Thereby we highlight a role for FMRP network genes in ASD.