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In the present study, we aimed to establish and characterize a mature cortical spheroid model system for Kleefstra syndrome (KS) using patient-derived iPSC. We identified key differences in the growth behavior of KS spheroids determined by reduced proliferation marked by low Ki67 and high E-cadherin expression. Conversely, in the spheroid-based neurite outgrowth assay KS outperformed the control neurite outgrowth due to higher BDNF expression. KS spheroids were highly enriched in VGLUT1/2-expressing glutamatergic and ChAT-expressing cholinergic neurons, while TH-positive catecholamine neurons were significantly underrepresented. Furthermore, high NMDAR1 expression was also detected in the KS spheroid, similarly to other patients-derived neuronal cultures, denoting high NMDAR1 expression as a general, KS-specific marker. Control and KS neuronal progenitors and neurospheres were exposed to different toxicants (paraquat, rotenone, bardoxolone, and doxorubicin), and dose-response curves were assessed after acute exposure. Differentiation stage and compound-specific differences were detected with KS neurospheres being the most sensitive to paraquat. Altogether this study describes a robust 3D model system expressing the disease-specific markers and recapitulating the characteristic pathophysiological traits. This platform is suitable for testing developing brain-adverse environmental effects interactions, drug development, and screening towards individual therapeutic strategies. [ABSTRACT FROM AUTHOR]

Objective: Kleefstra Syndrome (KS) is a rare genetic disorder caused by a deletion at 9q34.3. Studies showed that various heart defects are observed in 41–43% of patients and abnormal features on brain imaging in 58–63%. To date, the prenatal phenotype in KS has yet to be defined. Case report: We present the first prenatal diagnosis and chromosomal microarray analysis (CMA) of a case of 9q34.3 microdeletion in a fetus with increased amniotic fluid, supported by abnormal prenatal ultrasound findings, and confirmed via autopsy. CMA revealed a 2.1 Mb 9q34.3 microdeletion encompassing an OMIM gene of EHMT1, which is consistent with the diagnosis of Kleefstra syndrome and 9q subtelomeric deletion syndrome. Conclusion: When a fetus with normal karyotype presents with polyhydramnios or abnormalities noted during second-trimester prenatal ultrasound screening, CMA analysis can be considered as the next step to rule out or confirm the diagnosis of chromosomal or other genetic aberrations.

Abstract In the present study, we aimed to establish and characterize a mature cortical spheroid model system for Kleefstra syndrome (KS) using patient-derived iPSC. We identified key differences in the growth behavior of KS spheroids determined by reduced proliferation marked by low Ki67 and high E-cadherin expression. Conversely, in the spheroid-based neurite outgrowth assay KS outperformed the control neurite outgrowth due to higher BDNF expression. KS spheroids were highly enriched in VGLUT1/2-expressing glutamatergic and ChAT-expressing cholinergic neurons, while TH-positive catecholamine neurons were significantly underrepresented. Furthermore, high NMDAR1 expression was also detected in the KS spheroid, similarly to other patients-derived neuronal cultures, denoting high NMDAR1 expression as a general, KS-specific marker. Control and KS neuronal progenitors and neurospheres were exposed to different toxicants (paraquat, rotenone, bardoxolone, and doxorubicin), and dose-response curves were assessed after acute exposure. Differentiation stage and compound-specific differences were detected with KS neurospheres being the most sensitive to paraquat. Altogether this study describes a robust 3D model system expressing the disease-specific markers and recapitulating the characteristic pathophysiological traits. This platform is suitable for testing developing brain-adverse environmental effects interactions, drug development, and screening towards individual therapeutic strategies.

Trithorax-related H3K4 methyltransferases, KMT2C and KMT2D, are critical epigenetic modifiers. Haploinsufficiency of KMT2C was only recently recognized as a cause of neurodevelopmental disorder (NDD), so the clinical and molecular spectrums of the KMT2C -related NDD (now designated as Kleefstra syndrome 2) are largely unknown. We ascertained 98 individuals with rare KMT2C variants, including 75 with protein-truncating variants (PTVs). Notably, ∼15% of KMT2C PTVs were inherited. Although the most highly expressed KMT2C transcript consists of only the last four exons, pathogenic PTVs were found in almost all the exons of this large gene. KMT2C variant interpretation can be challenging due to segmental duplications and clonal hematopoesis-induced artifacts. Using samples from 27 affected individuals, divided into discovery and validation cohorts, we generated a moderate strength disorder-specific KMT2C DNA methylation (DNAm) signature and demonstrate its utility in classifying non-truncating variants. Based on 81 individuals with pathogenic/likely pathogenic variants, we demonstrate that the KMT2C -related NDD is characterized by developmental delay, intellectual disability, behavioral and psychiatric problems, hypotonia, seizures, short stature, and other comorbidities. The facial module of PhenoScore, applied to photographs of 34 affected individuals, reveals that the KMT2C -related facial gestalt is significantly different from the general NDD population. Finally, using PhenoScore and DNAm signatures, we demonstrate that the KMT2C -related NDD is clinically and epigenetically distinct from Kleefstra and Kabuki syndromes. Overall, we define the clinical features, molecular spectrum, and DNAm signature of the KMT2C -related NDD and demonstrate they are distinct from Kleefstra and Kabuki syndromes highlighting the need to rename this condition. Pathogenic KMT2C variants cause a disorder, which was named Kleefstra syndrome 2, suggesting its clinical features are highly similar to Kleefstra syndrome. In this study, we delineate the clinical and molecular features of this disorder and show that it is, in fact, different from both Kleefstra and Kabuki syndromes. [ABSTRACT FROM AUTHOR]

The shift to a genotype-first approach in genetic diagnostics has revolutionized our understanding of neurodevelopmental disorders, expanding both their molecular and phenotypic spectra. Kleefstra syndrome (KLEFS1) is caused by EHMT1 haploinsufficiency and exhibits broad clinical manifestations. EHMT1 encodes euchromatic histone methyltransferase-1—a pivotal component of the epigenetic machinery. We have recruited 209 individuals with a rare EHMT1 variant and performed comprehensive molecular in silico and in vitro testing alongside DNA methylation (DNAm) signature analysis for the identified variants. We (re)classified the variants as likely pathogenic/pathogenic (molecularly confirming Kleefstra syndrome) in 191 individuals. We provide an updated and broader clinical and molecular spectrum of Kleefstra syndrome, including individuals with normal intelligence and familial occurrence. Analysis of the EHMT1 variants reveals a broad range of molecular effects and their associated phenotypes, including distinct genotype-phenotype associations. Notably, we showed that disruption of the "reader" function of the ankyrin repeat domain by a protein altering variant (PAV) results in a KLEFS1-specific DNAm signature and milder phenotype, while disruption of only "writer" methyltransferase activity of the SET domain does not result in KLEFS1 DNAm signature or typical KLEFS1 phenotype. Similarly, N-terminal truncating variants result in a mild phenotype without the DNAm signature. We demonstrate how comprehensive variant analysis can provide insights into pathogenesis of the disorder and DNAm signature. In summary, this study presents a comprehensive overview of KLEFS1 and EHMT1, revealing its broader spectrum and deepening our understanding of its molecular mechanisms, thereby informing accurate variant interpretation, counseling, and clinical management. Kleefstra syndrome is a rare neurodevelopmental disorder caused by pathogenic EHMT1 variants affecting multiple organ systems. After almost two decades of research, we describe the current knowledge of EHMT1 variants and their functional consequences, leading to a broad clinical spectrum. Finally, we also obtained important insights into EHMT1 functions. [ABSTRACT FROM AUTHOR]

Objectives Kleefstra Syndrome (KS) is a rare genetic neurodevelopmental disorder caused by a microdeletion in chromosomal region 9q34.3 or a mutation in the euchromatin histone methyltransferase 1 (EHTM1) gene. Patients with KS show a range of clinical symptoms, including delay in motor and speech development, intellectual disability, autistic-like features, childhood hypotonia, and distinctive facial dysmorphic features. The patient is a four-year-old girl who was initially diagnosed with developmental motor delay by a pediatric neurologist and referred to an occupational therapy clinic at the age of six months. The initial assessment showed hypotonia and difficulties with rolling. Occupational therapy intervention was based on principles of neurodevelopmental treatment and sensory integration (SI) with cognitive integration and activities of daily living (ADL) training. With continuous occupational therapy services over more than three years, she overcame many disabilities and improved in occupational performance skills such as gross and fine motor skills as well as cognitive abilities, although her verbal communication skills were not effective. The patient's progress was as follows: she began rolling over at seven months, achieved independent sitting at ten months, crawled at eighteen months, stood with support at twenty months, and took her first steps at twenty-six months. The predominant problem was speech delay, which was noticeable in this syndrome. When a patient is being referred because of KS, occupational and speech therapy assessments should be accurately implemented. [ABSTRACT FROM AUTHOR]

Objective: Kleefstra syndrome (KS), formerly known as 9q subtelomeric deletion syndrome, is characterized by multiple structural abnormalities. However, most fetuses do not have obvious abnormal phenotypes. In this study, the fetus with KS presented with multiple system structural anomalies, and we aimed to explore the genotype-phenotype correlations of KS fetuses. Case report: Multiple systematic structural anomalies, including severe intrauterine growth restriction (IUGR) and cardiac defects, were detected by ultrasound in the fetus at 33 + 5 weeks' gestation. These abnormalities may be caused by the pathogenic deleted fragment at 9q34.3, including the euchromatic histone methyltransferase 1 (EHMT1) and collagen type V alpha 1 chain (COL5A1) genes, detected by copy number variation sequencing (CNV-seq). Conclusions: It is essential for clinicians to perform CNV-seq combined with multidisciplinary consultation for suspected KS fetuses, especially those with multiple systematic structural anomalies.

Mendelian neurodevelopmental disorders caused by variants in genes encoding chromatin modification can be categorized as Mendelian disorders of the epigenetic machinery (MDEMs). These disorders have significant overlap in molecular pathways and phenotypes including intellectual disability, short stature, and obesity. Among the MDEMs is Kleefstra syndrome (KLFS), which is caused by haploinsufficiency of EHMT1. Preclinical studies have identified metabolic dysregulation and obesity in KLFS models, but proper clinical translation lacks. In this study, we aim to delineate growth, body composition, and endocrine‐metabolic characteristics in a total of 62 individuals with KLFS. Our results revealed a high prevalence of childhood‐onset overweight/obesity (60%; 28/47) with disproportionately high body fat percentage, which aligns perfectly with previous preclinical studies. Short stature was common (33%), likely due to advanced skeletal maturation. Endocrine‐metabolic investigations showed thyroid dysregulation (22%; 9/41), elevated triglycerides, and decreased blood ammonia levels. Moreover, hand radiographs identified decreased bone mineralization (57%; 8/14) and negative ulnar variance (71%; 10/14). Our findings indicate a high (cardio)metabolic risk in KLFS. Therefore, we recommend monitoring of weight and endocrine‐metabolic profile. Supporting a healthy lifestyle and screening of bone mineralization is advised. Our comprehensive results support translational research and contribute to a better understanding of MDEM‐associated phenotypes. [ABSTRACT FROM AUTHOR]

Aims Kleefstra syndrome (KS), often diagnosed in early childhood, is a rare genetic disorder due to haploinsufficiency of EHMT1 and is characterized by neuromuscular and intellectual developmental abnormalities. Although congenital heart disease (CHD) is common, the prevalence of arrhythmias and CHD subtypes in KS is unknown. Methods and results Inspired by a novel case series of KS patients with atrial tachyarrhythmias in the USA, we evaluate the two largest known KS registries for arrhythmias and CHD: Radboudumc (50 patients) based on health record review at Radboud University Medical Center in the Netherlands and GenIDA (163 patients) based on worldwide surveys of patient families. Three KS patients (aged 17–25 years) presented with atrial tachyarrhythmias without manifest CHD. In the international KS registries, the median [interquartile range (IQR)] age was considerably younger: GenIDA/Radboudumc at 10/13.5 (12/13) years, respectively. Both registries had a 40% prevalence of cardiovascular abnormalities, the majority being CHD, including septal defects, vascular malformations, and valvular disease. Interestingly, 4 (8%) patients in the Radboudumc registry reported arrhythmias without CHD, including one atrial fibrillation (AF), two with supraventricular tachycardias, and one with non-sustained ventricular tachycardia. The GenIDA registry reported one patient with AF and another with chronic ectopic atrial tachycardia (AT). In total, atrial tachyarrhythmias were noted in six young KS patients (6/213 or 3%) with at least four (three AF and one AT) without structural heart disease. Conclusion In addition to a high prevalence of CHD, evolving data reveal early-onset atrial tachyarrhythmias in young KS patients, including AF, even in the absence of structural heart disease. [ABSTRACT FROM AUTHOR]

to report the first case series of Brazilian children diagnosed with Kleefstra syndrome, present a possible phenotype expansion to the syndrome and to raise physicians' awareness for this rare disease. seven patients with confirmed KS were evaluated, including 5 males and 2 females. Abnormal prenatal findings were observed in 4 patients. Most patients were born at term, with normal birth measurements. All patients had neurodevelopmental delay and 6 evolved with intellectual disability. Hearing loss was present in 57.1% of patients and 28.7% had congenital heart disease. In males, cryptorchidism was present in 75%. Despite the facial dysmorphisms, only 2 out of 7 patients had a pre-test clinical suspicion of KS. One specific patient presented bilateral agenesis of the semicircular canals, a very rare ear manifestation in Kleefstra syndrome, representing a possible phenotype expansion of the syndrome. this report aims to promote awareness among physicians evaluating patients in a context of neurodevelopmental delay or congenital malformations, especially congenital heart defects. We also highlight a possible phenotype expansion of the syndrome, with a case of semicircular anomaly, not reported in this syndrome so far. [ABSTRACT FROM AUTHOR]

Objective: Kleefstra Syndrome (KS) is a rare genetic disorder caused by a deletion at 9q34.3. Studies showed that various heart defects are observed in 41-43% of patients and abnormal features on brain imaging in 58-63%. To date, the prenatal phenotype in KS has yet to be defined., Case Report: We present the first prenatal diagnosis and chromosomal microarray analysis (CMA) of a case of 9q34.3 microdeletion in a fetus with increased amniotic fluid, supported by abnormal prenatal ultrasound findings, and confirmed via autopsy. CMA revealed a 2.1 Mb 9q34.3 microdeletion encompassing an OMIM gene of EHMT1, which is consistent with the diagnosis of Kleefstra syndrome and 9q subtelomeric deletion syndrome., Conclusion: When a fetus with normal karyotype presents with polyhydramnios or abnormalities noted during second-trimester prenatal ultrasound screening, CMA analysis can be considered as the next step to rule out or confirm the diagnosis of chromosomal or other genetic aberrations., Competing Interests: Declaration of competing interest The authors declare no conflicts of interest in connection with this article., (Copyright © 2024. Published by Elsevier B.V.)

Kleefstra syndrome (KLEFS1) is a rare genetic neurodevelopmental disorder affecting multiple body systems. It continues to be under-researched, and its prevalence remains unknown. This paper builds on the international KLEFS1 cohort of 172 individuals based on the caregiver-reported outcomes collected within the online data collection platform GenIDA and reports the occurrence, frequency and severity of symptoms in KLEFS1. The study clearly shows the importance of caregiver-reported outcomes collections in the rare disease domain. Moreover, the study emphasizes the need for more specific and enhanced data collection methods, suggesting recommendations to optimize caregiver-reported registries and foster an even more profound understanding of rare diseases., Competing Interests: Declaration of competing interest Authors have no relevant conflicts of interest to disclose., (Copyright © 2024 The Author(s). Published by Elsevier Masson SAS.. All rights reserved.)