Epilepsy in KAT6A syndrome: Description of two individuals and revision of the literature

The winged helix domain of MORF binds CpG islands and the TAZ2 domain of p300

Acetylation of histones by lysine acetyltransferases (KATs) provides a fundamental mechanism by which chromatin structure and transcriptional programs are regulated. Here, we describe a dual binding activity of the first winged helix domain of human MORF KAT (MORFWH1) that recognizes the TAZ2 domain of p300 KAT (p300TAZ2) and CpG rich DNA sequences. Structural and biochemical studies identified distinct DNA and p300TAZ2 binding sites, allowing MORFWH1 to independently engage either ligand. Genomic data show that MORF/MOZWH1 colocalizes with H3K18ac, a product of enzymatic activity of p300, on CpG rich promoters of target genes. Our findings suggest a functional cooperation of MORF and p300 KATs in transcriptional regulation.

Fetal hepatic calcification in severe KAT6A (Arboleda-Tham) syndrome

Arboleda-Tham syndrome (ARTHS, MIM 616268) is a rare genetic disease, due to a pathogenic variant of Lysine (K) Acetyltransferase 6A (KAT6A) with autosomal dominant inheritance. Firstly described in 2015, ARTHS is one of the more common causes of undiagnosed syndromic intellectual disability. Due to extreme phenotypic variability, ARTHS clinical diagnosis is challenging, mostly at early stage of the disease. Moreover, because of the wide and unspecific spectrum of ARTHS, identification of the syndrome during prenatal life rarely occurs. Therefore, reported cases of KAT6A syndrome have been identified primarily through clinical or research exome sequencing in a gene-centric approach. In order to expands the genotypic and phenotypic spectrum of ARTHS, we describe prenatal and postnatal findings in a patient with a novel frameshift KAT6A pathogenic variant, displaying a severe phenotype with previously unreported clinical features.

MORF and MOZ acetyltransferases target unmethylated CpG islands through the winged helix domain

Human acetyltransferases MOZ and MORF are implicated in chromosomal translocations associated with aggressive leukemias. Oncogenic translocations involve the far amino terminus of MOZ/MORF, the function of which remains unclear. Here, we identified and characterized two structured winged helix (WH) domains, WH1 and WH2, in MORF and MOZ. WHs bind DNA in a cooperative manner, with WH1 specifically recognizing unmethylated CpG sequences. Structural and genomic analyses show that the DNA binding function of WHs targets MORF/MOZ to gene promoters, stimulating transcription and H3K23 acetylation, and WH1 recruits oncogenic fusions to HOXA genes that trigger leukemogenesis. Cryo-EM, NMR, mass spectrometry and mutagenesis studies provide mechanistic insight into the DNA-binding mechanism, which includes the association of WH1 with the CpG-containing linker DNA and binding of WH2 to the dyad of the nucleosome. The discovery of WHs in MORF and MOZ and their DNA binding functions could open an avenue in developing therapeutics to treat diseases associated with aberrant MOZ/MORF acetyltransferase activities.

The clinical spectrum of a nonsense mutation in KAT6A: a case report

KAT6A syndrome is an autosomal dominant genetic disorder associated with intellectual disability due to mutations in the lysine acetyltransferase 6A (KAT6A) gene. There are some differences in phenotype between KAT6A gene variants. This current case report describes a 1-month-old male infant that had a nonsense mutation in the KAT6A gene. Neither of his parents had the mutation. The proband had feeding difficulties and a physical examination revealed the following: moderate dysphagia, hypoplastic laryngeal cartilage, poor audio-visual response, poor head-up ability, no active grasping awareness, microcephaly, high arched palate and he was significantly behind other children of the same age. Echocardiography showed that the foramen ovale was not closed. He was diagnosed with atrial septal defect (ASD) when 2 years old. The patient received ASD repair at 32 months of age. Head colour Doppler ultrasonography and brain magnetic resonance imaging showed cysts in the right ventricle and choroid plexus, which returned to normal at 2 years of age. This current case demonstrates that immediate surgery should be considered in newborns with KAT6A syndrome presenting with a heart malformation. A new KAT6A syndrome phenotype is described in this current case report, which requires early diagnosis and treatment.