Neuroimaging in Kabuki syndrome and another KMT2D-related disorder

Newly recognized orbital malformations in kabuki syndrome: A case report

Kabuki syndrome (KS) is a rare congenital disorder with distinctive characteristics. Herein, we describe a KS patient carrying a novel mutation in the KMT2D gene, c.11785C > T (p.Gln3929*). The patient presented with typical eyelid deformities, including eversion of the lateral lower eyelids, long palpebral fissures, hypertelorism, and medial epicanthus. Orbital computed tomography revealed orbital bone malformation with temporally and inferiorly displaced zygomatic bone. The bilateral orbits were shallow with an enlarged angle between the lateral walls. Zygomatic and maxillary bone dysplasia were also observed. Orbital bone anomalies are thought to be one of the characteristics of KS.

KMT2D preferentially binds mRNAs of the genes it regulates, suggesting a role in RNA processing

Histone lysine methyltransferases (HKMTs) perform vital roles in cellular life by controlling gene expression programs through the posttranslational modification of histone tails. Since many of them are intimately involved in the development of different diseases, including several cancers, understanding the molecular mechanisms that control their target recognition and activity is vital for the treatment and prevention of such conditions. RNA binding has been shown to be an important regulatory factor in the function of several HKMTs, such as the yeast Set1 and the human Ezh2. Moreover, many HKMTs are capable of RNA binding in the absence of a canonical RNA binding domain. Here, we explored the RNA binding capacity of KMT2D, one of the major H3K4 monomethyl transferases in enhancers, using RNA immunoprecipitation followed by sequencing. We identified a broad range of coding and non-coding RNAs associated with KMT2D and confirmed their binding through RNA immunoprecipitation and quantitative PCR. We also showed that a separated RNA binding region within KMT2D is capable of binding a similar RNA pool, but differences in the binding specificity indicate the existence of other regulatory elements in the sequence of KMT2D. Analysis of the bound mRNAs revealed that KMT2D preferentially binds co-transcriptionally to the mRNAs of the genes under its control, while also interacting with super enhancer- and splicing-related non-coding RNAs. These observations, together with the nuclear colocalization of KMT2D with differentially phosphorylated forms of RNA Polymerase II suggest a so far unexplored role of KMT2D in the RNA processing of the nascent transcripts.

Conductive Hearing Loss in Children

A variety of congenital and acquired disorders result in pediatric conductive hearing loss. Malformations of the external auditory canal are invariably associated with malformations of the middle ear space and ossicles. Isolated ossicular malformations are uncommon. Syndromes associated with external and middle ear malformations are frequently associated with abnormal development of first and second pharyngeal arch derivatives. Chronic inflammatory disorders include cholesteatoma, cholesterol granuloma, and tympanosclerosis.

Peripheral blood DNA methylation and neuroanatomical responses to HDACi treatment that rescues neurological deficits in a Kabuki syndrome mouse model

BACKGROUND

Recent findings from studies of mouse models of Mendelian disorders of epigenetic machinery strongly support the potential for postnatal therapies to improve neurobehavioral and cognitive deficits. As several of these therapies move into human clinical trials, the search for biomarkers of treatment efficacy is a priority. A potential postnatal treatment of Kabuki syndrome type 1 (KS1), caused by pathogenic variants in KMT2D encoding a histone-lysine methyltransferase, has emerged using a mouse model of KS1 (Kmt2d+/βGeo). In this mouse model, hippocampal memory deficits are ameliorated following treatment with the histone deacetylase inhibitor (HDACi), AR-42. Here, we investigate the effect of both Kmt2d+/βGeo genotype and AR-42 treatment on neuroanatomy and on DNA methylation (DNAm) in peripheral blood. While peripheral blood may not be considered a "primary tissue" with respect to understanding the pathophysiology of neurodevelopmental disorders, it has the potential to serve as an accessible biomarker of disease- and treatment-related changes in the brain.

METHODS

Half of the KS1 and wildtype mice were treated with 14 days of AR-42. Following treatment, fixed brain samples were imaged using MRI to calculate regional volumes. Blood was assayed for genome-wide DNAm at over 285,000 CpG sites using the Illumina Infinium Mouse Methylation array. DNAm patterns and brain volumes were analyzed in the four groups of animals: wildtype untreated, wildtype AR-42 treated, KS1 untreated and KS1 AR-42 treated.

RESULTS

We defined a DNAm signature in the blood of KS1 mice, that overlapped with the human KS1 DNAm signature. We also found a striking 10% decrease in total brain volume in untreated KS1 mice compared to untreated wildtype, which correlated with DNAm levels in a subset KS1 signature sites, suggesting that disease severity may be reflected in blood DNAm. Treatment with AR-42 ameliorated DNAm aberrations in KS1 mice at a small number of signature sites.

CONCLUSIONS

As this treatment impacts both neurological deficits and blood DNAm in mice, future KS clinical trials in humans could be used to assess blood DNAm as an early biomarker of therapeutic efficacy.

Re: "Next generation sequencing in neonatology: what does it mean for the next generation?"

Available evidence does not support limiting the use of rapid or ultra-rapid exome or genome sequencing in critically ill neonates to cases of predicted high diagnostic yield. Such testing is best positioned to improve neonatal care when test utilization is conceptualized within the total care of the family with a goal of rapid resolution of the diagnostic odyssey.

Chromatin Structure and Dynamics: Focus on Neuronal Differentiation and Pathological Implication

Chromatin structure is an essential regulator of gene expression. Its state of compaction contributes to the regulation of genetic programs, in particular during differentiation. Epigenetic processes, which include post-translational modifications of histones, DNA methylation and implication of non-coding RNA, are powerful regulators of gene expression. Neurogenesis and neuronal differentiation are spatio-temporally regulated events that allow the formation of the central nervous system components. Here, we review the chromatin structure and post-translational histone modifications associated with neuronal differentiation. Studying the impact of histone modifications on neuronal differentiation improves our understanding of the pathophysiological mechanisms of chromatinopathies and opens up new therapeutic avenues. In addition, we will discuss techniques for the analysis of histone modifications on a genome-wide scale and the pathologies associated with the dysregulation of the epigenetic machinery.