Christodoulou, John

Abstract There are ~100 genes or copy number variants (CNVs) used in genetic testing for Autism Spectrum Disorder (ASD, or autism). These genes are protein-coding, and the associated phenotypes often extend beyond socio-behavioral traits seen in autism including cognitive/medical complexities, epilepsy, and ADHD. Here, we characterize 27 males with ASD through whole genome sequencing (WGS), delineating X-chromosome microdeletions that implicate the long non-coding RNA (lncRNA) PTCHD1-AS as an ASD-susceptibility gene (OR=2.56, p=0.01). Two Ptchd1-as knockout (KO) murine models, created by removing the evolutionarily conserved exon-3, show ASD-like features in males, increasing repetitive behaviors and impairing typical social behavior and communication without overt cognitive comorbidities or ADHD-like behaviors. Hippocampus-dependent synaptic function, complex learning, and locomotor activity are unaffected in KO mice. Native nuclear-enriched mouse Ptchd1-as showed sustained expression from post-natal day-7 onward in the dorsal striatum, a predominantly GABAergic brain region implicated in ASD. Multi-omics revealed transcriptomic alterations in striatal oligodendrocyte, astrocyte and neurons impacting myelination and plasticity pathways. Disrupting Ptchd1-as led to reductions in conventional Protein Kinase-C, altered Src and GSK3α/β phosphorylation, and an enhancement of synaptic plasticity (long-term potentiation and long-term depression). Together, these findings implicate striatal molecular and circuit level dysregulation via Ptchd1-as in ASD etiology.

Humans with monogenic inborn errors responsible for extreme disease phenotypes can reveal essential physiological pathways. We investigated germline mutations in GNAI2 , which encodes G αi2 , a key component in heterotrimeric G protein signal transduction usually thought to regulate adenylyl cyclase–mediated cyclic adenosine monophosphate (cAMP) production. Patients with activating G αi2 mutations had clinical presentations that included impaired immunity. Mutant G αi2 impaired cell migration and augmented responses to T cell receptor (TCR) stimulation. We found that mutant G αi2 influenced TCR signaling by sequestering the guanosine triphosphatase (GTPase)–activating protein RASA2, thereby promoting RAS activation and increasing downstream extracellular signal–regulated kinase (ERK)/mitogen-activated protein kinase (MAPK) and phosphatidylinositol 3-kinase (PI3K)–AKT S6 signaling to drive cellular growth and proliferation.

Abstract Pathogenic variants in ALG13 ( ALG13 UDP‐N‐acetylglucosaminyltransferase subunit ) cause an X‐linked congenital disorder of glycosylation (ALG13‐CDG) where individuals have variable clinical phenotypes that include developmental delay, intellectual disability, infantile spasms, and epileptic encephalopathy. Girls with a recurrent de novo c.3013C>T; p.(Asn107Ser) variant have normal transferrin glycosylation. Using a highly sensitive, semi‐quantitative flow injection‐electrospray ionization‐quadrupole time‐of‐flight mass spectrometry (ESI‐QTOF/MS) N‐glycan assay, we report subtle abnormalities in N‐glycans that normally account for <0.3% of the total plasma glycans that may increase up to 0.5% in females with the p.(Asn107Ser) variant. Among our 11 unrelated ALG13‐CDG individuals, one male had abnormal serum transferrin glycosylation. We describe seven previously unreported subjects including three novel variants in ALG13 and report a milder neurodevelopmental course. We also summarize the molecular, biochemical, and clinical data for the 53 previously reported ALG13‐CDG individuals. We provide evidence that ALG13 pathogenic variants may mildly alter N‐linked protein glycosylation in both female and male subjects, but the underlying mechanism remains unclear.

Abstract Asparagine‐linked glycosylation 13 homolog ( ALG13 ) encodes a nonredundant, highly conserved, X‐linked uridine diphosphate (UDP)‐ N ‐acetylglucosaminyltransferase required for the synthesis of lipid linked oligosaccharide precursor and proper N‐linked glycosylation. De novo variants in ALG13 underlie a form of early infantile epileptic encephalopathy known as EIEE36, but given its essential role in glycosylation, it is also considered a congenital disorder of glycosylation (CDG), ALG13‐CDG. Twenty‐four previously reported ALG13‐CDG cases had de novo variants, but surprisingly, unlike most forms of CDG, ALG13‐CDG did not show the anticipated glycosylation defects, typically detected by altered transferrin glycosylation. Structural homology modeling of two recurrent de novo variants, p.A81T and p.N107S, suggests both are likely to impact the function of ALG13. Using a corresponding ALG13‐deficient yeast strain, we show that expressing yeast ALG13 with either of the highly conserved hotspot variants rescues the observed growth defect, but not its glycosylation abnormality. We present molecular and clinical data on 29 previously unreported individuals with de novo variants in ALG13 . This more than doubles the number of known cases. A key finding is that a vast majority of the individuals presents with West syndrome, a feature shared with other CDG types. Among these, the initial epileptic spasms best responded to adrenocorticotropic hormone or prednisolone, while clobazam and felbamate showed promise for continued epilepsy treatment. A ketogenic diet seems to play an important role in the treatment of these individuals.