A De Novo Missense Variant in EZH1 Associated With Developmental Delay Exhibits Functional Deficits in Drosophila melanogaster

Authors

Sharayu V Jangam
Lauren C Briere
Kristy L Jay
Jonathan C Andrews
Melissa A Walker
Lance H Rodan
Frances A High
Undiagnosed Diseases Network
Shinya Yamamoto
David A Sweetser
Michael F Wangler

Publication Date

8-9-2023

Journal

Genetics

DOI

10.1093/genetics/iyad110

PMID

37314226

PMCID

PMC10411565

PubMedCentral® Posted Date

6-14-2023

PubMedCentral® Full Text Version

Post-print

Published Open-Access

yes

Keywords

Abnormalities, Multiple, Enhancer of Zeste Homolog 2 Protein, Drosophila melanogaster, Craniofacial Abnormalities, Drosophila, Humans, Histones, Congenital Hypothyroidism, Animals, Hand Deformities, Congenital, Polycomb Repressive Complex 2, Drosophila melanogaster, EZH1, E(z), H3K27-trimethylation, rare undiagnosed disease, polycomb repressive complex 2, patterning defect, missense, developmental delay

Abstract

EZH1, a polycomb repressive complex-2 component, is involved in a myriad of cellular processes. EZH1 represses transcription of downstream target genes through histone 3 lysine27 (H3K27) trimethylation (H3K27me3). Genetic variants in histone modifiers have been associated with developmental disorders, while EZH1 has not yet been linked to any human disease. However, the paralog EZH2 is associated with Weaver syndrome. Here we report a previously undiagnosed individual with a novel neurodevelopmental phenotype identified to have a de novo missense variant in EZH1 through exome sequencing. The individual presented in infancy with neurodevelopmental delay and hypotonia and was later noted to have proximal muscle weakness. The variant, p.A678G, is in the SET domain, known for its methyltransferase activity, and an analogous somatic or germline mutation in EZH2 has been reported in patients with B-cell lymphoma or Weaver syndrome, respectively. Human EZH1/2 are homologous to fly Enhancer of zeste (E(z)), an essential gene in Drosophila, and the affected residue (p.A678 in humans, p.A691 in flies) is conserved. To further study this variant, we obtained null alleles and generated transgenic flies expressing wildtype [E(z)WT] and the variant [E(z)A691G]. When expressed ubiquitously the variant rescues null-lethality similar to the wildtype. Overexpression of E(z)WT induces homeotic patterning defects but notably the E(z)A691G variant leads to dramatically stronger morphological phenotypes. We also note a dramatic loss of H3K27me2 and a corresponding increase in H3K27me3 in flies expressing E(z)A691G, suggesting this acts as a gain-of-function allele. In conclusion, here we present a novel EZH1 de novo variant associated with a neurodevelopmental disorder. Furthermore, we found that this variant has a functional impact in Drosophila.