PTPN4 germline variants result in aberrant neurodevelopment and growth.

Protein-tyrosine phosphatases (PTPs) are pleomorphic regulators of eukaryotic cellular responses to extracellular signals that function by modulating the phosphotyrosine of specific proteins. A handful of PTPs have been implicated in germline and somatic human disease. Using exome sequencing, we identified missense and truncating variants in PTPN4 in six unrelated individuals with varying degrees of intellectual disability or developmental delay. The variants occurred de novo in all five subjects in whom segregation analysis was possible. Recurring features include postnatal growth deficiency or excess, seizures, and, less commonly, structural CNS, heart, or skeletal anomalies. PTPN4 is a widely expressed protein tyrosine phosphatase that regulates neuronal cell homeostasis by protecting neurons against apoptosis. We suggest that pathogenic variants in PTPN4 confer risk for growth and cognitive abnormalities in humans.

Disruption of CTNND2, encoding delta-catenin, causes a penetrant attention deficit disorder and myopia.

Attention deficit hyperactivity disorder (ADHD) is a common and highly heritable neurodevelopmental disorder with poorly understood pathophysiology and genetic mechanisms. A balanced chromosomal translocation interrupts CTNND2 in several members of a family with profound attentional deficit and myopia, and disruption of the gene was found in a separate unrelated individual with ADHD and myopia. CTNND2 encodes a brain-specific member of the adherens junction complex essential for postsynaptic and dendritic development, a site of potential pathophysiology in attentional disorders. Therefore, we propose that the severe and highly penetrant nature of the ADHD phenotype in affected individuals identifies CTNND2 as a potential gateway to ADHD pathophysiology similar to the DISC1 translocation in psychosis or AUTS2 in autism.

Concise Review: Induced Pluripotent Stem Cell Models for Neuropsychiatric Diseases.

The major neuropsychiatric conditions of schizophrenia, affective disorders, and infantile autism are characterized by chronic symptoms of episodic, stable, or progressive nature that result in significant morbidity. Symptomatic treatments are the mainstay but do not resolve the underlying disease processes, which are themselves poorly understood. The prototype psychotropic drugs are of variable efficacy, with therapeutic mechanisms of action that are still uncertain. Thus, neuropsychiatric disorders are ripe for new technologies and approaches with the potential to revolutionize mechanistic understanding and drive the development of novel targeted treatments. The advent of methods to produce patient-derived stem cell models and three-dimensional organoids with the capacity to differentiate into neurons and the various neuronal cellular lineages mark such an advance. We discuss numerous techniques involved, their applications, and areas that require further optimization. Stem Cells Translational Medicine 2017;6:2062-2070.

Redefining the MED13L syndrome.

Congenital cardiac and neurodevelopmental deficits have been recently linked to the mediator complex subunit 13-like protein MED13L, a subunit of the CDK8-associated mediator complex that functions in transcriptional regulation through DNA-binding transcription factors and RNA polymerase II. Heterozygous MED13L variants cause transposition of the great arteries and intellectual disability (ID). Here, we report eight patients with predominantly novel MED13L variants who lack such complex congenital heart malformations. Rather, they depict a syndromic form of ID characterized by facial dysmorphism, ID, speech impairment, motor developmental delay with muscular hypotonia and behavioral difficulties. We thereby define a novel syndrome and significantly broaden the clinical spectrum associated with MED13L variants. A prominent feature of the MED13L neurocognitive presentation is profound language impairment, often in combination with articulatory deficits.

Monoallelic expression of the human FOXP2 speech gene.

The recent descriptions of widespread random monoallelic expression (RMAE) of genes distributed throughout the autosomal genome indicate that there are more genes subject to RMAE on autosomes than the number of genes on the X chromosome where X-inactivation dictates RMAE of X-linked genes. Several of the autosomal genes that undergo RMAE have independently been implicated in human Mendelian disorders. Thus, parsing the relationship between allele-specific expression of these genes and disease is of interest. Mutations in the human forkhead box P2 gene, FOXP2, cause developmental verbal dyspraxia with profound speech and language deficits. Here, we show that the human FOXP2 gene undergoes RMAE. Studying an individual with developmental verbal dyspraxia, we identify a deletion 3 Mb away from the FOXP2 gene, which impacts FOXP2 gene expression in cis. Together these data suggest the intriguing possibility that RMAE impacts the haploinsufficiency phenotypes observed for FOXP2 mutations.

Function of rhodopsin in temperature discrimination in Drosophila.

Many animals, including the fruit fly, are sensitive to small differences in ambient temperature. The ability of Drosophila larvae to choose their ideal temperature (18°C) over other comfortable temperatures (19° to 24°C) depends on a thermosensory signaling pathway that includes a heterotrimeric guanine nucleotide-binding protein (G protein), a phospholipase C, and the transient receptor potential TRPA1 channel. We report that mutation of the gene (ninaE) encoding a classical G protein-coupled receptor (GPCR), Drosophila rhodopsin, eliminates thermotactic discrimination in the comfortable temperature range. This role for rhodopsin in thermotaxis toward 18°C was light-independent. Introduction of mouse melanopsin restored normal thermotactic behavior in ninaE mutant larvae. We propose that rhodopsins represent a class of evolutionarily conserved GPCRs that are required for initiating thermosensory signaling cascades.

A novel hypomorphic MECP2 point mutation is associated with a neuropsychiatric phenotype.

The MECP2 gene on Xq28 encodes a transcriptional repressor, which binds to and modulates expression of active genes. Mutations in MECP2 cause classic or preserved speech variant Rett syndrome and intellectual disability in females and early demise or marked neurodevelopmental handicap in males. The consequences of a hypomorphic Mecp2 allele were recently investigated in a mouse model, which developed obesity, motor, social, learning, and behavioral deficits, predicting a human neurobehavioral syndrome. Here, we describe mutation analysis of a nondysmorphic female proband and her father who presented with primarily neuropsychiatric manifestations and obesity with relative sparing of intelligence, language, growth, and gross motor skills. We identified and characterized a novel missense mutation (c.454C>G; p.P152A) in the critical methyl-binding domain of MeCP2 that disrupts MeCP2 functional activity. We show that a gradient of impairment is present when the p.P152A mutation is compared with an allelic p.P152R mutation, which causes classic Rett syndrome and another Rett syndrome-causing mutation, such that protein-heterochromatin binding observed by immunofluorescence and immunoblotting is wild-type > P152A > P152R > T158 M, consistent with the severity of the observed phenotype. Our findings provide evidence for very mild phenotypes in humans associated with partial reduction of MeCP2 function arising from subtle variation in MECP2.

A novel mutation in JARID1C/SMCX in a patient with autism spectrum disorder (ASD).

We describe a nondysmorphic patient with developmental delay and autism spectrum disorder who has a missense mutation in the Jumonji AT-rich interactive domain 1C (JARID1C) gene. This child first presented at 30 months of age with stereotyped and repetitive behaviors, impairment in social reciprocity and in the use of multiple nonverbal behaviors, and developmental delay primarily in the language domain. A diagnosis of autism was made and subsequently confirmed at the current age of 47 months. Cytogenetic and fragile X studies were normal. Mutational analysis revealed a novel missense mutation in exon 16 of the JARID1C gene that results in an arginine to tryptophan substitution at amino acid 766 (R766W). Sequence alignment analysis with multiple available eukaryotic sequences including the homologous proteins of mouse and zebrafish demonstrated that the affected amino acid is conserved. JARID1C has not previously been implicated in autism susceptibility. Recent novel molecular evidence suggests that it is a histone demethylase specific for di- and trimethylated histone 3 lysine 4 (H3K4) and functions as a transcriptional repressor by fostering REST-mediated neuronal gene regulation. The JARID1C-regulated genes SCN2A, CACNA1H, BDNF, and SLC18A1 have previously been associated with autism and cognitive dysfunction. This patient brings the total number of reported JARID1C mutations to 14. This presentation both extends the range of neurocognitive phenotypes attributable to mutations in this gene and illustrates the importance of molecular studies and DNA sequence analysis for accurate diagnosis of monogenic causes of autism.