Clinical delineation, sex differences, and genotype-phenotype correlation in pathogenic KDM6A variants causing X-linked Kabuki syndrome type 2

Next generation phenotyping for diagnosis and phenotype-genotype correlations in Kabuki syndrome

The field of dysmorphology has been changed by the use Artificial Intelligence (AI) and the development of Next Generation Phenotyping (NGP). The aim of this study was to propose a new NGP model for predicting KS (Kabuki Syndrome) on 2D facial photographs and distinguish KS1 (KS type 1, KMT2D-related) from KS2 (KS type 2, KDM6A-related). We included retrospectively and prospectively, from 1998 to 2023, all frontal and lateral pictures of patients with a molecular confirmation of KS. After automatic preprocessing, we extracted geometric and textural features. After incorporation of age, gender, and ethnicity, we used XGboost (eXtreme Gradient Boosting), a supervised machine learning classifier. The model was tested on an independent validation set. Finally, we compared the performances of our model with DeepGestalt (Face2Gene). The study included 1448 frontal and lateral facial photographs from 6 centers, corresponding to 634 patients (527 controls, 107 KS); 82 (78%) of KS patients had a variation in the KMT2D gene (KS1) and 23 (22%) in the KDM6A gene (KS2). We were able to distinguish KS from controls in the independent validation group with an accuracy of 95.8% (78.9-99.9%, p < 0.001) and distinguish KS1 from KS2 with an empirical Area Under the Curve (AUC) of 0.805 (0.729-0.880, p < 0.001). We report an automatic detection model for KS with high performances (AUC 0.993 and accuracy 95.8%). We were able to distinguish patients with KS1 from KS2, with an AUC of 0.805. These results outperform the current commercial AI-based solutions and expert clinicians.

KMT2D Deficiency Causes Sensorineural Hearing Loss in Mice and Humans

Individuals with Kabuki syndrome type 1 (KS1) often have hearing loss recognized in middle childhood. Current clinical dogma suggests that this phenotype is caused by frequent infections due to the immune deficiency in KS1 and/or secondary to structural abnormalities of the ear. To clarify some aspects of hearing loss, we collected information on hearing status from 21 individuals with KS1 and found that individuals have both sensorineural and conductive hearing loss, with the average age of presentation being 7 years. Our data suggest that while ear infections and structural abnormalities contribute to the observed hearing loss, these factors do not explain all loss. Using a KS1 mouse model, we found hearing abnormalities from hearing onset, as indicated by auditory brainstem response measurements. In contrast to mouse and human data for CHARGE syndrome, a disorder possessing overlapping clinical features with KS and a well-known cause of hearing loss and structural inner ear abnormalities, there are no apparent structural abnormalities of the cochlea in KS1 mice. The KS1 mice also display diminished distortion product otoacoustic emission levels, which suggests outer hair cell dysfunction. Combining these findings, our data suggests that KMT2D dysfunction causes sensorineural hearing loss compounded with external factors, such as infection.

Developmental transcriptomic patterns can be altered by transgenic overexpression of Uty

The genetic material encoded on X and Y chromosomes provides the foundation by which biological sex differences are established. Epigenetic regulators expressed on these sex chromosomes, including Kdm6a (Utx), Kdm5c, and Ddx3x have far-reaching impacts on transcriptional control of phenotypic sex differences. Although the functionality of UTY (Kdm6c, the Y-linked homologue of UTX), has been supported by more recent studies, its role in developmental sex differences is not understood. Here we test the hypothesis that UTY is an important transcriptional regulator during development that could contribute to sex-specific phenotypes and disease risks across the lifespan. We generated a random insertion Uty transgenic mouse (Uty-Tg) to overexpress Uty. By comparing transcriptomic profiles in developmental tissues, placenta and hypothalamus, we assessed potential UTY functional activity, comparing Uty-expressing female mice (XX + Uty) with wild-type male (XY) and female (XX) mice. To determine if Uty expression altered physiological or behavioral outcomes, adult mice were phenotypically examined. Uty expression masculinized female gene expression patterns in both the placenta and hypothalamus. Gene ontology (GO) and gene set enrichment analysis (GSEA) consistently identified pathways including immune and synaptic signaling as biological processes associated with UTY. Interestingly, adult females expressing Uty gained less weight and had a greater glucose tolerance compared to wild-type male and female mice when provided a high-fat diet. Utilizing a Uty-overexpressing transgenic mouse, our results provide novel evidence as to a functional transcriptional role for UTY in developing tissues, and a foundation to build on its prospective capacity to influence sex-specific developmental and health outcomes.

Identification of a KDM6A somatic mutation responsible for Kabuki syndrome by excluding a conflicting KMT2D germline variant through episignature analysis

Kabuki syndrome (KS) is a congenital disorder caused by mutations in either KMT2D on chromosome 12 or KDM6A on chromosome X, encoding a lysine methyltransferase and a lysine demethylase, respectively. A 9-year-4-month-old male patient with a normal karyotype presented with KS and autism spectrum disorder. Genetic testing for KS was conducted by Sanger sequencing and episignature analysis using DNA methylation array data. The patient had a mosaic stop-gain variant in KDM6A and a heterozygous missense variant (rs201078160) in KMT2D. The KDM6A variant is expected to be deleterious. The KMT2D variant pathogenicity has been inconsistently reported in the ClinVar database. Using biobanking resources, we identified two heterozygous individuals possessing the rs201078160 variant. In a subsequent episignature analysis, the KS patient showed the KS episignature, but two control individuals with the rs201078160 variant did not. Our results indicate that the mosaic stop-gained variant in KDM6A, but not the rs201078160 variant in KMT2D, is responsible for the KS phenotype in the patient. This study further demonstrated the utility of DNA methylation information in diagnosing rare genetic diseases and emphasized the importance of a reference dataset containing both genotype and DNA methylation information.

X Chromosome Factor Kdm6a Enhances Cognition Independent of Its Demethylase Function in the Aging XY Male Brain

Males exhibit shorter life span and more cognitive deficits, in the absence of dementia, in aging human populations. In mammals, the X chromosome is enriched for neural genes and is a major source of biologic sex difference, in part, because males show decreased expression of select X factors (XY). While each sex (XX and XY) harbors one active X due to X chromosome inactivation in females, some genes, such as Kdm6a, transcriptionally escape silencing in females-resulting in lower transcript levels in males. Kdm6a is a known histone demethylase (H3K27me2/3) with multiple functional domains that is linked with synaptic plasticity and cognition. Whether elevating Kdm6a could benefit the aged male brain and whether this requires its demethylase function remains unknown. We used lentiviral-mediated overexpression of the X factor in the hippocampus of aging male mice and tested their cognition and behavior in the Morris water-maze. We found that acutely increasing Kdm6a-in a form without demethylase function-selectively improved learning and memory, in the aging XY brain, without altering total activity or anxiety-like measures. Further understanding the demethylase-independent downstream mechanisms of Kdm6a may lead to novel therapies for treating age-induced cognitive deficits in both sexes.

Congenital hyperinsulinemic hypoglycemia (HH) requiring treatment as the presenting feature of Kabuki syndrome

Kabuki syndrome is a congenital condition characterized by a set of facial dysmorphic features that often help the clinician to suspect the diagnosis. However, more insidious symptoms can rarely occur, such as manifestations of hypoglycemia in newborns with congenital hyperinsulinism hypoglycemia, especially when a variant of the KDM6A gene is found. In those cases, a treatment with diazoxide can be started and can be replaced with lanreotide if a satisfying glycemic control is not achieved. We report the case of a female patient born at 37 weeks of gestational age, without any obvious facial dysmorphic features, after a non-complicated pregnancy, that presented with feeding difficulties, drowsiness, and irritability revealing a hyperinsulinemic hypoglycemia. Further testing at 6 months old found a KDM6A mutation. The patient was initially treated by diazoxide alone, but its dosage had to be lowered because of the occurrence of treatment side effects, and lanreotide had been added to maintain acceptable blood sugar levels. A congenital hyperinsulinemia hypoglycemia revealed heterozygous truncating variant in the KDM6A gene, also known as X-linked Kabuki syndrome in a newborn. In cases of neonatal hypoglycemia, the first-line therapy is diazoxide. Our report shows that analogues of somatostatin such as lanreotide should be considered if the diazoxide regimen is not tolerated.

The clinical and molecular spectrum of the KDM6B-related neurodevelopmental disorder

De novo variants are a leading cause of neurodevelopmental disorders (NDDs), but because every monogenic NDD is different and usually extremely rare, it remains a major challenge to understand the complete phenotype and genotype spectrum of any morbid gene. According to OMIM, heterozygous variants in KDM6B cause "neurodevelopmental disorder with coarse facies and mild distal skeletal abnormalities." Here, by examining the molecular and clinical spectrum of 85 reported individuals with mostly de novo (likely) pathogenic KDM6B variants, we demonstrate that this description is inaccurate and potentially misleading. Cognitive deficits are seen consistently in all individuals, but the overall phenotype is highly variable. Notably, coarse facies and distal skeletal anomalies, as defined by OMIM, are rare in this expanded cohort while other features are unexpectedly common (e.g., hypotonia, psychosis, etc.). Using 3D protein structure analysis and an innovative dual Drosophila gain-of-function assay, we demonstrated a disruptive effect of 11 missense/in-frame indels located in or near the enzymatic JmJC or Zn-containing domain of KDM6B. Consistent with the role of KDM6B in human cognition, we demonstrated a role for the Drosophila KDM6B ortholog in memory and behavior. Taken together, we accurately define the broad clinical spectrum of the KDM6B-related NDD, introduce an innovative functional testing paradigm for the assessment of KDM6B variants, and demonstrate a conserved role for KDM6B in cognition and behavior. Our study demonstrates the critical importance of international collaboration, sharing of clinical data, and rigorous functional analysis of genetic variants to ensure correct disease diagnosis for rare disorders.

Insights into the genotype-phenotype relationship of ocular manifestations in Kabuki syndrome

We aim to assess if genotype-phenotype correlations are present within ocular manifestations of Kabuki syndrome (KS) among a large multicenter cohort. We conducted a retrospective, medical record review including clinical history and comprehensive ophthalmological examinations of a total of 47 individuals with molecularly confirmed KS and ocular manifestations at Boston Children's Hospital and Cincinnati Children's Hospital Medical Center. We assessed information regarding ocular structural, functional, and adnexal elements as well as pertinent associated phenotypic features associated with KS. For both type 1 KS (KS1) and type 2 KS (KS2), we observed more severe eye pathology in nonsense variants towards the C-terminus of each gene, KMT2D and KDM6A, respectively. Furthermore, frameshift variants appeared to be not associated with structural ocular elements. Between both types of KS, ocular structural elements were more frequently identified in KS1 compared with KS2, which only involved the optic disc in our cohort. These results reinforce the need for a comprehensive ophthalmologic exam upon diagnosis of KS and regular follow-up exams. The specific genotype may allow risk stratification of the severity of the ophthalmologic manifestation. However, additional studies involving larger cohorts are needed to replicate our observations and conduct powered analyses to more formally risk-stratify based on genotype, highlighting the importance of multicenter collaborations in rare disease research.

Dynamic changes in intestinal microbiota and metabolite composition of pre-weaned beef calves

Gut microbes and their metabolites are essential for maintaining host health and production. The intestinal microflora of pre-weaned calves gradually tends to mature with growth and development and has high plasticity, but few studies have explored the dynamic changes of intestinal microbiota and metabolites in pre-weaned beef calves. In this study, we tracked the dynamics of faecal microbiota in 13 new-born calves by 16S rRNA gene sequencing and analysed changes in faecal amino acid levels using metabolomics. Calves were divided into the relatively high average daily gain group (HA) and the relatively low average daily gain group (LA) for comparison. The results demonstrated that the alpha diversity of the faecal microbiota increased with calf growth and development. The abundance of Porphyromonadaceae bacterium DJF B175 increased in the HA group, while that of Lactobacillus reuteri decreased. The results of the LEfSe analysis showed that the microbiota of faeces of HA calves at eight weeks of age was enriched with P. bacterium DJF B175, while Escherichia coli and L. reuteri were enriched in the microbiota of faeces of LA calves. Besides, the total amino acid concentration decreased significantly in the eighth week compared with that in the first week (P < 0.05). Overall, even under the same management conditions, microorganisms and their metabolites interact to play different dynamic regulatory roles. Our results provide new insights into changes in the gut microbiota and metabolites of pre-weaned calves.

Xp11.3 microdeletion causing Norrie disease and X-linked Kabuki syndrome

Purpose

To describe a novel case of Norrie disease and X-linked Kabuki syndrome caused by a microdeletion encompassing multiple genes on the X chromosome.

Observations

A 3-day-old boy born at full term had bilateral retrolental fibrovascular plaques. Surgery with lensectomy and vitrectomy revealed bilateral, closed funnel retinal detachments consistent with a clinical diagnosis of Norrie disease. In addition, the baby had congenital heart defects, hearing loss, and dysmorphic facies. His mother carried a clinical diagnosis of Kabuki syndrome. Genetic testing of the baby revealed an Xp11.3 microdeletion that included the NDP and KDM6A genes, confirming the baby had both Norrie disease and X-linked Kabuki syndrome. The mother was found via ultrawide-field fluorescein angiography to have asymptomatic peripheral retinal vascular anomalies, consistent with NDP-associated familial exudative vitreoretinopathy (FEVR).

Conclusions and importance

This is the first reported case of Norrie disease together with X-linked Kabuki syndrome. Contiguous gene deletions may explain some of the variable systemic involvement in Norrie disease.

Molecular characterization of an embryonal rhabdomyosarcoma occurring in a patient with Kabuki syndrome: report and literature review in the light of tumor predisposition syndromes

Kabuki syndrome is a well-recognized syndrome characterized by facial dysmorphism and developmental delay/intellectual disability and in the majority of patients a germline variant in KMT2D is found. As somatic KMT2D variants can be found in 5-10% of tumors a tumor predisposition in Kabuki syndrome is discussed. So far less than 20 patients with Kabuki syndrome and a concomitant malignancy have been published. Here we report on a female patient with Kabuki syndrome and a c.2558_2559delCT germline variant in KMT2D who developed an embryonal rhabdomyosarcoma (ERMS) at 10 years. On tumor tissue we performed DNA-methylation profiling and exome sequencing (ES). Copy number analyses revealed aneuploidies typical for ERMS including (partial) gains of chromosomes 2, 3, 7, 8, 12, 15, and 20 and 3 focal deletions of chromosome 11p. DNA methylation profiling mapped the case to ERMS by a DNA methylation-based sarcoma classifier. Sequencing suggested gain of the wild-type KMT2D allele in the trisomy 12. Including our patient literature review identified 18 patients with Kabuki syndrome and a malignancy. Overall, the landscape of malignancies in patients with Kabuki syndrome was reminiscent of that of the pediatric population in general. Histopathological and molecular data were only infrequently reported and no report included next generation sequencing and/or DNA-methylation profiling. Although we found no strong arguments pointing towards KS as a tumor predisposition syndrome, based on the small numbers any relation cannot be fully excluded. Further planned studies including profiling of additional tumors and long term follow-up of KS-patients into adulthood could provide further insights.

A narrative review on pathogenetic mechanisms of hyperinsulinemic hypoglycemia in Kabuki syndrome

Objective. Kabuki syndrome (KS) is associated with hyperinsulinemic hypoglycemia (HH) in 0.3-4% of patients, thus exceeding the prevalence in the general population. HH association is stronger for KS type 2 (KDM6A-KS, OMIM #300867) than KS type 1 (KMT2D-KS, OMIM #147920). Both the disease-associated genes, KMD6A and KMT2D, modulate the chromatin dynamic. As such, KS is considered to be the best characterized pediatric chromatinopathy. However, the exact pathogenetic mechanisms leading to HH in this syndrome remain still unclear. Methods. We selected on the electronic database PubMed all articles describing or hypothesizing the mechanisms underlying the dysregulated insulin secretion in KS. Results. The impact on the gene expression due to the KDM6A or KMT2D function loss may lead to a deregulated pancreatic β-cell differentiation during embryogenesis. Moreover, both KMT2D gene and KDM6A gene are implicated in promoting the transcription of essential pancreatic β-cell genes and in regulating the metabolic pathways instrumental for insulin release. Somatic KMT2D or KDM6A mutations have also been described in several tumor types, including insulinoma, and have been associated with metabolic pathways promoting pancreatic cell proliferation. Conclusions. The impact of pathogenic variants in KDM6A and KDM2D genes on β-cell insulin release remains to be fully clarified. Understanding this phenomenon may provide valuable insight into the physiological mechanisms of insulin release and into the pathological cascade causing hyperinsulinism in KS. The identification of these molecular targets may open new therapeutic opportunities based on epigenetic modifiers.

Syndromic forms of congenital hyperinsulinism

Congenital hyperinsulinism (CHI), also called hyperinsulinemic hypoglycemia (HH), is a very heterogeneous condition and represents the most common cause of severe and persistent hypoglycemia in infancy and childhood. The majority of cases in which a genetic cause can be identified have monogenic defects affecting pancreatic β-cells and their glucose-sensing system that regulates insulin secretion. However, CHI/HH has also been observed in a variety of syndromic disorders. The major categories of syndromes that have been found to be associated with CHI include overgrowth syndromes (e.g. Beckwith-Wiedemann and Sotos syndromes), chromosomal and monogenic developmental syndromes with postnatal growth failure (e.g. Turner, Kabuki, and Costello syndromes), congenital disorders of glycosylation, and syndromic channelopathies (e.g. Timothy syndrome). This article reviews syndromic conditions that have been asserted by the literature to be associated with CHI. We assess the evidence of the association, as well as the prevalence of CHI, its possible pathophysiology and its natural course in the respective conditions. In many of the CHI-associated syndromic conditions, the mechanism of dysregulation of glucose-sensing and insulin secretion is not completely understood and not directly related to known CHI genes. Moreover, in most of those syndromes the association seems to be inconsistent and the metabolic disturbance is transient. However, since neonatal hypoglycemia is an early sign of possible compromise in the newborn, which requires immediate diagnostic efforts and intervention, this symptom may be the first to bring a patient to medical attention. As a consequence, HH in a newborn or infant with associated congenital anomalies or additional medical issues remains a differential diagnostic challenge and may require a broad genetic workup.

Sex-biased and parental allele-specific gene regulation by KDM6A

Background

KDM6A is a demethylase encoded by a gene with female-biased expression due to escape from X inactivation. Its main role is to facilitate gene expression through removal of the repressive H3K27me3 mark, with evidence of some additional histone demethylase-independent functions. KDM6A mutations have been implicated in congenital disorders such as Kabuki Syndrome, as well as in sex differences in cancer.

Methods

Kdm6a was knocked out using CRISPR/Cas9 gene editing in F1 male and female mouse embryonic stem cells (ES) derived from reciprocal crosses between C57BL6 x Mus castaneus. Diploid and allelic RNA-seq analyses were done to compare gene expression between wild-type and Kdm6a knockout (KO) clones. The effects of Kdm6a KO on sex-biased gene expression were investigated by comparing gene expression between male and female ES cells. Changes in H3K27me3 enrichment and chromatin accessibility at promoter regions of genes with expression changes were characterized by ChIP-seq and ATAC-seq followed by diploid and allelic analyses.

Results

We report that Kdm6a KO in male and female embryonic stem (ES) cells derived from F1 hybrid mice cause extensive gene dysregulation, disruption of sex biases, and specific parental allele effects. Among the dysregulated genes are candidate genes that may explain abnormal developmental features of Kabuki syndrome caused by KDM6A mutations in human. Strikingly, Kdm6a knockouts result in a decrease in sex-biased expression and in preferential downregulation of the maternal alleles of a number of genes. Most promoters of dysregulated genes show concordant epigenetic changes including gain of H3K27me3 and loss of chromatin accessibility, but there was less concordance when considering allelic changes.

Conclusions

Our study reveals new sex-related roles of KDM6A in the regulation of developmental genes, the maintenance of sex-biased gene expression, and the differential expression of parental alleles.

Genetics and Epigenetics of the X and Y Chromosomes in the Sexual Differentiation of the Brain

For many decades to date, neuroendocrinologists have delved into the key contribution of gonadal hormones to the generation of sex differences in the developing brain and the expression of sex-specific physiological and behavioral phenotypes in adulthood. However, it was not until recent years that the role of sex chromosomes in the matter started to be seriously explored and unveiled beyond gonadal determination. Now we know that the divergent evolutionary process suffered by X and Y chromosomes has determined that they now encode mostly dissimilar genetic information and are subject to different epigenetic regulations, characteristics that together contribute to generate sex differences between XX and XY cells/individuals from the zygote throughout life. Here we will review and discuss relevant data showing how particular X- and Y-linked genes and epigenetic mechanisms controlling their expression and inheritance are involved, along with or independently of gonadal hormones, in the generation of sex differences in the brain.

Epigenetic modifier Kdm6a/Utx controls the specification of hypothalamic neuronal subtypes in a sex-dependent manner

Kdm6a is an X-chromosome-linked H3K27me2/3 demethylase that promotes chromatin accessibility and gene transcription and is critical for tissue/cell-specific differentiation. Previous results showed higher Kdm6a levels in XX than in XY hypothalamic neurons and a female-specific requirement for Kdm6a in mediating increased axogenesis before brain masculinization. Here, we explored the sex-specific role of Kdm6a in the specification of neuronal subtypes in the developing hypothalamus. Hypothalamic neuronal cultures were established from sex-segregated E14 mouse embryos and transfected with siRNAs to knockdown Kdm6a expression (Kdm6a-KD). We evaluated the effect of Kdm6a-KD on Ngn3 expression, a bHLH transcription factor regulating neuronal sub-specification in hypothalamus. Kdm6a-KD decreased Ngn3 expression in females but not in males, abolishing basal sex differences. Then, we analyzed Kdm6a-KD effect on Ascl1, Pomc, Npy, Sf1, Gad1, and Th expression by RT-qPCR. While Kdm6a-KD downregulated Ascl1 in both sexes equally, we found sex-specific effects for Pomc, Npy, and Th. Pomc and Th expressed higher in female than in male neurons, and Kdm6a-KD reduced their levels only in females, while Npy expressed higher in male than in female neurons, and Kdm6a-KD upregulated its expression only in females. Identical results were found by immunofluorescence for Pomc and Npy neuropeptides. Finally, using ChIP-qPCR, we found higher H3K27me3 levels at Ngn3, Pomc, and Npy promoters in male neurons, in line with Kdm6a higher expression and demethylase activity in females. At all three promoters, Kdm6a-KD induced an enrichment of H3K27me3 only in females. These results indicate that Kdm6a plays a sex-specific role in controlling the expression of transcription factors and neuropeptides critical for the differentiation of hypothalamic neuronal populations regulating food intake and energy homeostasis.

From Genotype to Phenotype-A Review of Kabuki Syndrome

Kabuki syndrome (KS) is a rare neuro-developmental disorder caused by variants in genes of histone modification, including KMT2D and KDM6A. This review assesses our current understanding of KS, which was originally named Niikawa-Kuroki syndrome, and aims to guide surveillance and medical care of affected individuals as well as identify gaps in knowledge and unmet patient needs. Ovid MEDLINE and EMBASE databases were searched from 1981 to 2021 to identify reports related to genotype and systems-based phenotype characterization of KS. A total of 2418 articles were retrieved, and 152 were included in this review, representing a total of 1369 individuals with KS. Genotype, phenotype, and the developmental and behavioral profile of KS are reviewed. There is a continuous clinical phenotype spectrum associated with KS with notable variability between affected individuals and an emerging genotype-phenotype correlation. The observed clinical variability may be attributable to differences in genotypes and/or unknown genetic and epigenetic factors. Clinical management is symptom oriented, fragmented, and lacks established clinical care standards. Additional research should focus on enhancing understanding of the burden of illness, the impact on quality of life, the adult phenotype, life expectancy and development of standard-of-care guidelines.

Comparison of methylation episignatures in KMT2B- and KMT2D-related human disorders

Aim & methods: To investigate peripheral blood methylation episignatures in KMT2B-related dystonia (DYT-KMT2B), the authors undertook genome-wide methylation profiling of ∼2 M CpGs using a next-generation sequencing-based assay and compared the findings with those in controls and patients with KMT2D-related Kabuki syndrome type 1 (KS1). Results: A total of 1812 significantly differentially methylated CpG positions (false discovery rate < 0.05) were detected in DYT-KMT2B samples compared with controls. Multi-dimensional scaling analysis showed that the 10 DYT-KMT2B samples clustered together and separately from 29 controls and 10 with pathogenic variants in KMT2D. The authors found that most differentially methylated CpG positions were specific to one disorder and that all (DYT-KMT2B) and most (Kabuki syndrome type 1) methylation alterations in CpG islands were gain of methylation events. Conclusion: Using sensitive methylation profiling methodology, the authors replicated recent reports of a methylation episignature for DYT-KMT2B. These findings will facilitate the development of episignature-based assays to improve diagnostic accuracy.

Hyperinsulinism

Congenital or monogenic hyperinsulinism (HI) is a group of rare genetic disorders characterized by dysregulated insulin secretion and is the most common cause of persistent hypoglycemia in children. Knowledge of normal glucose homeostasis allows for a better understanding of the underlying pathophysiology of hyperinsulinemic hypoglycemia, facilitating timely diagnosis and management. The goal of management is to prevent cerebral insults secondary to hypoglycemia, which can result in poor neurologic outcomes and intellectual disability. Responsiveness to diazoxide, the first-line pharmacologic therapy for persistent hypoglycemia, is also the first step to distinguishing the different genotypic causes of monogenic hyperinsulinism. Early genetic testing becomes necessary when monogenic HI is strongly considered. Knowledge of specific gene mutations allows the determination of a clinical prognosis and definite therapeutic options, such as identifying those with focal forms of hyperinsulinism, who may attain a complete cure through surgical removal of specific affected parts of the pancreas. However, the lack of identifiable cause in a considerable number of patients identified with HI suggests there may be other genetic loci that are yet to be discovered. Furthermore, continued research is needed to explore new forms of therapy, particularly in severe, diazoxide-nonresponsive cases.

DNA methylation episignature testing improves molecular diagnosis of Mendelian chromatinopathies

PURPOSE

Chromatinopathies include more than 50 disorders caused by disease-causing variants of various components of chromatin structure and function. Many of these disorders exhibit unique genome-wide DNA methylation profiles, known as episignatures. In this study, the methylation profile of a large cohort of individuals with chromatinopathies was analyzed for episignature detection.

METHODS

DNA methylation data was generated on extracted blood samples from 129 affected individuals with the Illumina Infinium EPIC arrays and analyzed using an established bioinformatic pipeline.

RESULTS

The DNA methylation profiles matched and confirmed the sequence findings in both the discovery and validation cohorts. Twenty-five affected individuals carrying a variant of uncertain significance, did not show a methylation profile matching any of the known episignatures. Three additional variant of uncertain significance cases with an identified KDM6A variant were re-classified as likely pathogenic (n = 2) or re-assigned as Wolf-Hirschhorn syndrome (n = 1). Thirty of the 33 Next Generation Sequencing negative cases did not match a defined episignature while three matched Kabuki syndrome, Rubinstein-Taybi syndrome and BAFopathy respectively.

CONCLUSION

With the expanding clinical utility of the EpiSign assay, DNA methylation analysis should be considered part of the testing cascade for individuals presenting with clinical features of Mendelian chromatinopathy disorders.

Sex Bias and Autoimmune Diseases

Sex bias in immune function has been well-described, and women have been shown to counter immunologically stimulating phenomena such as infection, malignancy, and trauma with more protective responses than men. Heightened immunity in women may also result in a predisposition for loss of self-tolerance and development of autoimmunity, reflected by the overwhelming female sex bias of patients with autoimmune diseases. In this review, we discuss the postulated evolutionary etiologies for sexual dimorphism in immunity. We also review the molecular mechanisms underlying divergent immune responses in men and women, including sex hormone effects, X chromosome dosage, and autosomal sex-biased genes. With increasing evidence that autoimmune disease susceptibility is influenced by numerous hormonal and genetic factors, a comprehensive understanding of these topics may facilitate the development of much-needed targeted therapeutics.