A novel cardiomyopathy phenotype linked to missense mutation of CHD7
Loss-of-function of the chromatin remodeler CHD7 causes CHARGE syndrome, characterized by variable penetrance and diverse abnormalities.  However, establishing genotype-phenotype correlations has been challenging, as most CHD7 inactivating mutations are null alleles.  Through CHD7 missense variant analysis at potential phosphorylation sites, we identified T730 (T720 in mice) as a critical residue associated with pathogenesis.  Using a CHD7 T730 missense mutation (Chd7T720A) and a frameshift null allele (Chd7fs) in a mouse model, we found that Chd7fs/fs mice were non-viable, while Chd7fs/+ mice exhibited haploinsufficiency-related circling behavior.  Notably, Chd7fs/T720A mice died before postnatal day 2, indicating the Chd7T720A allele is hypomorphic.  Micro-CT analysis at E18.5 revealed heterozygous mice primarily exhibited hypertrophic cardiomyopathy (HCM), while homozygous mice developed both HCM and dilated cardiomyopathy (DCM).  RNA-seq analysis of neonatal Chd7T720A/T720A hearts revealed a disrupted transcriptome, which in males and females was characterized by downregulation of mitochondrial energy metabolism genes and enrichment of ETS family transcription factor targets.  We further identified GSK3ß, GSK3a, HIPK1, and DYRK2 as candidate kinases for this site, suggesting a regulatory role in CHD7.  This missense mutation causing developmental heart abnormalities establishes the first genotype-phenotype correlation for CHD7, and offers new insights into CHARGE syndrome pathogenesis. Overall design: Mouse hearts from neonatal mice at postnatal day 0 (P0) were immediately processed for total RNA extraction.  The study included three biological replicates for each experimental group, encompassing male and female hearts of Chd7+/+, Chd7T720A/+, and Chd7T720A/T720A mice.