The clathrin adaptor complex responsible for somatodendritic protein sorting

Usmani-Riazuddin syndrome can have a recognizable phenotype: Report of a novel AP1G1 variant

Usmani-Riazuddin syndrome (USRISR, MIM# 619548; USRISD, MIM#619467) is a very rare genetic condition. recently associated with deleterious variants in AP1G1 (MIM* 603533). It is characterized by multisystemic involvement including intellectual disability, speech and developmental delay, behavioral anomalies, muscular tone disorders, seizures, limb defects, and unspecified facial gestalt. In this report, we describe this syndrome for the second time, in association to a novel AP1G1 variant identified in a toddler with multisystemic involvement including intellectual disability, speech and developmental delay, behavioral anomalies, arrhythmias, hearing loss, skin changes, and limb defects. Next generation sequencing (NGS) analysis through clinical exome disclosed AP1G1: c.1969C>G (p.Leu657Val), de novo, likely pathogenic variant, according to ACMG classification criteria. Proband's facial features resembled the spectrum of chromatinopathies. Clinical pictures were analyzed and a clinical overlap was supported by DeepGestalt analysis (www.face2gene.com). The system identified 6 chromatin disorders out of 30 possible diagnoses. The remaining 24 included 9 miscellaneous cryptic chromosomal abnormalities (excluded due to normal microarray study). To the best of our knowledge, this is the first description of likely distinctive facial features in a patient with Usmani-Riazuddin syndrome. Further multicentric analyses are needed for a better definition of this aspect.

De novo and bi-allelic variants in AP1G1 cause neurodevelopmental disorder with developmental delay, intellectual disability, and epilepsy

Adaptor protein (AP) complexes mediate selective intracellular vesicular trafficking and polarized localization of somatodendritic proteins in neurons. Disease-causing alleles of various subunits of AP complexes have been implicated in several heritable human disorders, including intellectual disabilities (IDs). Here, we report two bi-allelic (c.737C>A [p.Pro246His] and c.1105A>G [p.Met369Val]) and eight de novo heterozygous variants (c.44G>A [p.Arg15Gln], c.103C>T [p.Arg35Trp], c.104G>A [p.Arg35Gln], c.229delC [p.Gln77Lys^∗11], c.399_400del [p.Glu133Aspfs^∗37], c.747G>T [p.Gln249His], c.928-2A>C [p.?], and c.2459C>G [p.Pro820Arg]) in AP1G1, encoding gamma-1 subunit of adaptor-related protein complex 1 (AP1γ1), associated with a neurodevelopmental disorder (NDD) characterized by mild to severe ID, epilepsy, and developmental delay in eleven families from different ethnicities. The AP1γ1-mediated adaptor complex is essential for the formation of clathrin-coated intracellular vesicles. In silico analysis and 3D protein modeling simulation predicted alteration of AP1γ1 protein folding for missense variants, which was consistent with the observed altered AP1γ1 levels in heterologous cells. Functional studies of the recessively inherited missense variants revealed no apparent impact on the interaction of AP1γ1 with other subunits of the AP-1 complex but rather showed to affect the endosome recycling pathway. Knocking out ap1g1 in zebrafish leads to severe morphological defect and lethality, which was significantly rescued by injection of wild-type AP1G1 mRNA and not by transcripts encoding the missense variants. Furthermore, microinjection of mRNAs with de novo missense variants in wild-type zebrafish resulted in severe developmental abnormalities and increased lethality. We conclude that de novo and bi-allelic variants in AP1G1 are associated with neurodevelopmental disorder in diverse populations.