Anatomical and functional abnormalities on MRI in kabuki syndrome

Molecular insights of KMT2D and clinical aspects of Kabuki syndrome type 1

BACKGROUND

Kabuki syndrome type 1 (KS1), a rare multisystem congenital disorder, presents with characteristic facial features, intellectual disability, persistent fetal fingertip pads, skeletal abnormalities, and postnatal growth delays. KS1 results from pathogenic variants in the KMT2D gene, which encodes a histone methyltransferase protein involved in chromatin remodeling, promoter and enhancer regulation, and scaffold formation during early development. KMT2D also mediates cell signaling pathways, responding to external stimuli and organizing effector protein assembly. Research on KMT2D's molecular mechanisms in KS1 has primarily focused on its histone methyltransferase activity, leaving a gap in understanding the methyltransferase-independent roles in KS1 clinical manifestations.

METHODS

This scoping review examines KMT2D's role in gene expression regulation across various species, cell types, and contexts. We analyzed human pathogenic KMT2D variants using publicly available databases and compared them to research organism models of KS1. We also conducted a systematic search of healthcare and governmental databases for clinical trials, studies, and therapeutic approaches.

RESULTS

Our review highlights KMT2D's critical roles beyond methyltransferase activity in diverse cellular contexts and conditions. We identified six distinct groups of KMT2D as a cell signaling mediator, including evidence of methyltransferase-dependent and -independent activity. A comprehensive search of the literature, clinical databases, and public registries emphasizes the need for basic research on KMT2D's functional complexity and longitudinal studies of KS1 patients to establish objective outcome measurements for therapeutic development.

CONCLUSION

We discuss how KMT2D's role in translating external cellular communication can partly explain the clinical heterogeneity observed in KS1 patients. Additionally, we summarize the current molecular diagnostic approaches and clinical trials targeting KS1. This review is a resource for patient advocacy groups, researchers, and physicians to support KS1 diagnosis and therapeutic development.

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.

Development of prefrontal cortex

During evolution, the cerebral cortex advances by increasing in surface and the introduction of new cytoarchitectonic areas among which the prefrontal cortex (PFC) is considered to be the substrate of highest cognitive functions. Although neurons of the PFC are generated before birth, the differentiation of its neurons and development of synaptic connections in humans extend to the 3rd decade of life. During this period, synapses as well as neurotransmitter systems including their receptors and transporters, are initially overproduced followed by selective elimination. Advanced methods applied to human and animal models, enable investigation of the cellular mechanisms and role of specific genes, non-coding regulatory elements and signaling molecules in control of prefrontal neuronal production and phenotypic fate, as well as neuronal migration to establish layering of the PFC. Likewise, various genetic approaches in combination with functional assays and immunohistochemical and imaging methods reveal roles of neurotransmitter systems during maturation of the PFC. Disruption, or even a slight slowing of the rate of neuronal production, migration and synaptogenesis by genetic or environmental factors, can induce gross as well as subtle changes that eventually can lead to cognitive impairment. An understanding of the development and evolution of the PFC provide insight into the pathogenesis and treatment of congenital neuropsychiatric diseases as well as idiopathic developmental disorders that cause intellectual disabilities.

Clinical heterogeneity of Kabuki syndrome in a cohort of Italian patients and review of the literature

Kabuki syndrome (KS) is a well-recognized disorder characterized by postnatal growth deficiency, dysmorphic facial features, skeletal anomalies, and intellectual disability. The syndrome is caused by KMT2D gene mutations or less frequently KDM6A gene mutations or deletions. We report a systematic evaluation of KS patients from Campania region of Italy; data were also compared with literature ones. We collected data of 15 subjects (8 males and 7 females with age range 10-26 years; mean age 16.9 years) with confirmed diagnosis of KS, representing the entire cohort of patients from Campania Region. Each patient performed biochemical testing and instrumental investigation. Neuro-intellectual development, cranio-facial dysmorphisms, and multisystem involvement data were collected retrospectively. For each category, type of defects and frequency of the anomalies were analyzed. Our observation shows that KS patients from Campania region have some particular and previously underscored, neurological and immunological findings. We found high prevalence of EEG's abnormalities (43%) and MRI brain abnormalities (60%). Microcephaly resulted more common in our series (33%), if compared with major cohorts described in literature. Biochemical features of immunodeficiency and autoimmune diseases including thyroid autoimmunity, polyserositis, and vitiligo were observed with high prevalence (54.5%). Low immunoglobulins levels were a frequent finding. Lymphocyte class investigation showed significantly reduced CD8 levels in one patient.Conclusions: These data confirm great heterogeneity of clinical manifestations in KS and suggest to introduce further clinical diagnostic criteria in order to perform a correct and precocious diagnosis. What is Known • Kabuki syndrome is characterized by growth deficiency, dysmorphic facial features, skeletal anomalies, and intellectual disability • Immune dysfunction is a common finding but autoimmune diseases are rarely seen • Neurological features are common What is New • Some particular facial features could help gestalt diagnosis (hypertelorism, broad nasal bridge, micrognathia, tooth agenesis, cutaneous haemangiomas and strabismus) • Higher prevalence of autoimmune disorders than previously reported • Particular neurological features are present in this cohort (EEG and MRI brain abnormalities).

A Novel Intronic KMT2D Variant as a Cause of Kabuki Syndrome: A Case Report

Kabuki syndrome (KS) is an autosomal dominant genetic disorder in which most cases are caused by de novo mutations. KS type 1 is caused by mutations in KMT2D (OMIM: #147920) and is more common. KS type 2 is caused by mutations in KDM6A (OMIM: #300867). Both genes encode proteins that modify histones and are involved in epigenetic regulation. The enzyme histone-lysine N-methyltransferase 2D, the product of KMT2D, is expressed in most adult tissues and is essential for early embryonic development. The main clinical manifestations of KS include dysmorphic facial features, such as elongated palpebral fissures, eversion of the lateral third of the lower eyelids, and short nasal columella with a broad and depressed nasal tip. Additionally, patients also present with skeletal abnormalities, dermatoglyphic features, mild-to-moderate intellectual disability, hearing loss, and postnatal growth deficiency. We describe an 11-year-old girl from Colombia, who presented with characteristic clinical signs of KS. Genetic studies showed a KMT2D intronic variant (KMT2D NM_003482.3: c.511‐2A> T) as a cause of KS.

Volume of hippocampal subfields and cognitive deficits in neuromyelitis optica spectrum disorders

BACKGROUND

Aquaporin-4 (AQP4) water channel is involved in hippocampal plasticity and is the target of neuromyelitis optica spectrum disorders (NMOSD) autoimmunity. We measured volumes of hippocampal subfields and their association with cognitive performance in AQP4-seropositive NMOSD patients.

METHODS

Global and regional hippocampal volumes were derived from 28 AQP4-seropositive NMOSD patients and 101 healthy controls (HC) from 3D-T1-weighted images. Normalized brain volumes were also calculated. A neuropsychological evaluation, including the Brief Repeatable Battery of Neuropsychological Tests, was performed in patients. Based on HC data, we estimated mean z-scores of volumes in the whole NMOSD group and compared them according to the status of global and domain-selective cognitive impairment.

RESULTS

Global cognitive impairment was detected in 46.4% of NMOSD patients, with attentive (60.7%) and executive (21.4%) domains being the most affected. NMOSD patients had left hippocampal atrophy at global (p = 0.012) and regional level (fimbria, Cornu Ammonis [CA] 3, molecular layer, dentate gyrus [DG], and subicular complex, p values ranging between 0.033 and <0.001). On the right side the fimbria and hippocampal tail were atrophic (p = 0.024 for both). Cognitively impaired patients showed atrophy in the left CA3 and CA4 (p = 0.025-0.028), while patients presenting verbal and visual memory impairment had significant CA3 and DG atrophy. Those patients with attentive or executive impairment had preserved brain and hippocampal volumes.

CONCLUSIONS

NMOSD patients showed hippocampal atrophy associated with verbal and visual memory impairment. Such damage did not explain attention and executive function alterations, which were the most common cognitive deficits in this population.

Brain perfusion magnetic resonance imaging using pseudocontinuous arterial spin labeling in 314 dogs and cats

Background

Arterial spin labeling (ASL) is a noninvasive brain perfusion magnetic resonance imaging (MRI) technique that has not been assessed in clinical veterinary medicine.

Hypothesis/Objectives

To test the feasibility of ASL using a 1.5 Tesla scanner and provide recommendations for optimal quantification of cerebral blood flow (CBF) in dogs and cats.

Animals

Three hundred fourteen prospectively selected client‐owned dogs and cats.

Methods

Each animal underwent brain MRI including morphological sequences and ≥1 ASL sequences using different sites of blood labeling and postlabeling delays (PLD). Calculated ASL success rates were compared. The CBF was quantified in animals that had morphologically normal brain MRI results and parameters of ASL optimization were investigated.

Results

Arterial spin labeling was easily implemented with an overall success rate of 95% in animals with normal brain MRI. Technical recommendations included (a) positioning of the imaging slab at the foramen magnum and (b) selected PLD of 1025 ms in cats and dogs <7 kg, 1525 ms in dogs 7 to 38 kg, and 2025 ms in dogs >38 kg. In 37 dogs, median optimal CBF in the cortex and thalamic nuclei were 114 and 95 mL/100 g/min, respectively. In 28 cats, median CBF in the cortex and thalamic nuclei were 113 and 114 mL/100 g/min, respectively.

Conclusions and Clinical Importance

Our survey of brain perfusion ASL‐MRI demonstrated the feasibility of ASL at 1.5 Tesla, suggested technical recommendations and provided CBF values that should be helpful in the characterization of various brain diseases in dogs and cats.

Kabuki Syndrome-Clinical Review with Molecular Aspects

Kabuki syndrome (KS) is a rare developmental disorder principally comprised of developmental delay, hypotonia and a clearly defined dysmorphism: elongation of the structures surrounding the eyes, a shortened and depressed nose, thinning of the upper lip and thickening of the lower lip, large and prominent ears, hypertrichosis and scoliosis. Other characteristics include poor physical growth, cardiac, gastrointestinal and renal anomalies as well as variable behavioral issues, including autistic features. De novo or inherited pathogenic/likely pathogenic variants in the KMT2D gene are the most common cause of KS and account for up to 75% of patients. Variants in KDM6A cause up to 5% of cases (X-linked dominant inheritance), while the etiology of about 20% of cases remains unknown. Current KS diagnostic criteria include hypotonia during infancy, developmental delay and/or intellectual disability, typical dysmorphism and confirmed pathogenic/likely pathogenic variant in KMT2D or KDM6A. Care for KS patients includes the control of physical and psychomotor development during childhood, rehabilitation and multi-specialist care. This paper reviews the current clinical knowledge, provides molecular and scientific links and sheds light on the treatment of Kabuki syndrome individuals.

Lacrimal Puncta Agenesis in Kabuki Syndrome

Kabuki syndrome (KS) is a rare congenital disorder characterized by multiple systemic anomalies and facial characteristics. Here, the authors present the first case, to the best of the authors' knowledge, of bilateral lacrimal puncta agenesis in a patient with KS.#8232;The proband patient was a 29-year-old woman diagnosed with this syndrome, brought to our office due to recurrent conjunctivitis where agenesia of lacrimal puncta was observed. Therapeutic options were exposed but, as the concomitant medication (topiramate) produced ocular dryness, conservative treatment was decided. Diagnosis of KS is challenging because it is a complex syndrome with many associated findings. The authors recommend taking into account the agenesis of lacrimal points in the differential diagnosis of KS if it is associated with other phenotypic alterations as well as including lacrimal examination in patients with KS diagnosis. The authors emphasize the importance of individualizing treatment since drugs used for the systematic management of these patients can influence tear symptoms.

Inhibition of KDM1A activity restores adult neurogenesis and improves hippocampal memory in a mouse model of Kabuki syndrome

Kabuki syndrome (KS) is a rare cause of intellectual disability primarily caused by loss-of-function mutations in lysine-specific methyltransferase 2D (KMT2D), which normally adds methyl marks to lysine 4 on histone 3. Previous studies have shown that a mouse model of KS (Kmt2d^+/βGeo) demonstrates disruption of adult neurogenesis and hippocampal memory. Proof-of-principle studies have shown postnatal rescue of neurological dysfunction following treatments that promote chromatin opening; however, these strategies are non-specific and do not directly address the primary defect of histone methylation. Since lysine-specific demethylase 1A (LSD1/KDM1A) normally removes the H3K4 methyl marks added by KMT2D, we hypothesized that inhibition of KDM1A demethylase activity may ameliorate molecular and phenotypic defects stemming from KMT2D loss. To test this hypothesis, we evaluated a recently developed KDM1A inhibitor (TAK-418) in Kmt2d^+/βGeo mice. We found that orally administered TAK-418 increases the numbers of newly born doublecortin (DCX)⁺ cells and processes in the hippocampus in a dose-dependent manner. We also observed TAK-418-dependent rescue of histone modification defects in hippocampus both by western blot and chromatin immunoprecipitation sequencing (ChIP-seq). Treatment rescues gene expression abnormalities including those of immediate early genes such as FBJ osteosarcoma oncogene (Fos) and FBJ osteosarcoma oncogene homolog B (Fosb). After 2 weeks of TAK-418, Kmt2d^+/βGeo mice demonstrated normalization of hippocampal memory defects. In summary, our data suggest that KDM1A inhibition is a plausible treatment strategy for KS and support the hypothesis that the epigenetic dysregulation secondary to KMT2D dysfunction plays a major role in the postnatal neurological disease phenotype in KS.

Hypoglycemia and Dandy-Walker variant in a Kabuki syndrome patient: a case report

Background

Kabuki syndrome (KS) is a rare congenital condition with cardinal manifestations of typical facial features, developmental delays, skeletal anomalies, abnormal dermatoglyphic presentations, and mild to moderate intellectual disability. Pathogenic variants in two epigenetic modifier genes, KMT2D and KDM6A, are responsible for KS1 and KS2, respectively.

Case presentation

A Chinese girl had persistent neonatal hypoglycemia and Dandy-Walker variant. Whole-exome sequencing identified a novel single nucleotide deletion in KMT2D (NM_003482.3 c.12165del p.(Glu4056Serfs*10)) that caused frameshift and premature termination. The mutation was de novo. According to the American College of Medical Genetics and Genomics (ACMG) guidelines, this variant is considered pathogenic. The patient was diagnosed with KS by molecular testing.

Conclusion

A single novel mutation in KMT2D was identified in a KS patients with hypoglycemia and Dandy-Walker variant in the neonatal stage. A molecular test was conducted to diagnose KS at an early stage.

Holoprosencephaly in Kabuki syndrome

Kabuki syndrome is a rare, multi-systemic disorder of chromatin regulation due to mutations in either KMT2D or KDM6A that encode a H3K4 methyltransferase and an H3K27 demethylase, respectively. The associated clinical phenotype is a direct result of temporal and spatial changes in gene expression in various tissues including the brain. Although mild to moderate intellectual disability is frequently recognized in individuals with Kabuki syndrome, the identification of brain anomalies, mostly involving the hippocampus and related structures remains an exception. Recently, the first two cases with alobar holoprosencephaly and mutations in KMT2D have been reported in the medical literature. We identified a de novo, pathogenic KMT2D variant (c.6295C > T; p.R2099X) using trio whole-exome sequencing in a 2-year-old female with lobar holoprosencephaly, microcephaly and cranio-facial features of Kabuki syndrome. This report expands the spectrum of brain anomalies associated with Kabuki syndrome underscoring the important role of histone modification for early brain development.

Kabuki syndrome: novel pathogenic variants, new phenotypes and review of literature

Objective

This study describes 5 novel variants of 7 KMT2D/KDM6A gene and summarizes the clinical manifestations and the mutational spectrum of 47 Chinese Kabuki syndrome (KS) patients.

Methods

Blood samples were collected for whole-exome sequencing (WES) for 7 patients and their parents if available. Phenotypic and genotypic spectra of 40 previously published unrelated Chinese KS patients were summarized.

Result

Genetic sequencing identified six KMT2D variants (c.3926delC, c.5845delC, c.6595delT, c.12630delG, c.16294C > T, and c.16442delG) and one KDM6A variant (c.2668-2671del). Of them, 4 variants (c.3926delC, c.5845delC, c.12630delG, and c.16442delG) in KMT2D gene and the variant (c.2668-2671del) in KDM6A gene were novel. Combining with previously published Chinese KS cases, the patients presented with five cardinal manifestations including facial dysmorphism, intellectual disability, growth retardation, fingertip pads and skeletal abnormalities. In addition, 29.5% (5/17) patients had brain abnormalities, such as hydrocephalus, cerebellar vermis dysplasia, thin pituitary and white matter myelination delay, corpus callosum hypoplasia and Dandy-Walker malformation.

Conclusion

In this report, five novel variants in KMT2D/KDM6A genes are described. A subset of Chinese KS patients presented with brain abnormalities that were not previously reported. Our study expands the mutational and phenotypic spectra of KS.

Precocious neuronal differentiation and disrupted oxygen responses in Kabuki syndrome

Chromatin modifiers act to coordinate gene expression changes critical to neuronal differentiation from neural stem/progenitor cells (NSPCs). Lysine-specific methyltransferase 2D (KMT2D) encodes a histone methyltransferase that promotes transcriptional activation and is frequently mutated in cancers and in the majority (>70%) of patients diagnosed with the congenital, multisystem intellectual disability disorder Kabuki syndrome 1 (KS1). Critical roles for KMT2D are established in various non-neural tissues, but the effects of KMT2D loss in brain cell development have not been described. We conducted parallel studies of proliferation, differentiation, transcription, and chromatin profiling in KMT2D-deficient human and mouse models to define KMT2D-regulated functions in neurodevelopmental contexts, including adult-born hippocampal NSPCs in vivo and in vitro. We report cell-autonomous defects in proliferation, cell cycle, and survival, accompanied by early NSPC maturation in several KMT2D-deficient model systems. Transcriptional suppression in KMT2D-deficient cells indicated strong perturbation of hypoxia-responsive metabolism pathways. Functional experiments confirmed abnormalities of cellular hypoxia responses in KMT2D-deficient neural cells and accelerated NSPC maturation in vivo. Together, our findings support a model in which loss of KMT2D function suppresses expression of oxygen-responsive gene programs important to neural progenitor maintenance, resulting in precocious neuronal differentiation in a mouse model of KS1.