KMT2A (Lysine methyltransferase 2A) is a member of the epigenetic machinery, encoding a lysine methyltransferase responsible for the transcriptional activation through lysine 4 of histone 3 (H3K4) methylation. KMT2A has a crucial role in gene expression, thus it is associated to pathological conditions when found mutated. KMT2A germinal mutations are associated to Wiedemann–Steiner syndrome and also in patients with initial clinical diagnosis of several other chromatinopathies (i.e., Coffin–Siris syndromes, Kabuki syndrome, Cornelia De Lange syndrome, Rubinstein–Taybi syndrome), sharing an overlapping phenotype. On the other hand, KMT2A somatic mutations have been reported in several tumors, mainly blood malignancies. Due to its evolutionary conservation, the role of KMT2A in embryonic development, hematopoiesis and neurodevelopment has been explored in different animal models, and in recent decades, epigenetic treatments for disorders linked to KMT2A dysfunction have been extensively investigated. To note, pharmaceutical compounds acting on tumors characterized by KMT2A mutations have been formulated, and even nutritional interventions for chromatinopathies have become the object of study due to the role of microbiota in epigenetic regulation.

Cornelia de Lange Syndrome (CdLS) is a rare developmental disorder affecting a multitude of organs including the central nervous system, inducing a variable neurodevelopmental delay. CdLS malformations derive from the deregulation of developmental pathways, inclusive of the canonical WNT pathway. We have evaluated MRI anomalies and behavioral and neurological clinical manifestations in CdLS patients. Importantly, we observed in our cohort a significant association between behavioral disturbance and structural abnormalities in brain structures of hindbrain embryonic origin. Considering the cumulative evidence on the cohesin-WNT-hindbrain shaping cascade, we have explored possible ameliorative effects of chemical activation of the canonical WNT pathway with lithium chloride in different models: (I) Drosophila melanogaster CdLS model showing a significant rescue of mushroom bodies morphology in the adult flies; (II) mouse neural stem cells restoring physiological levels in proliferation rate and differentiation capabilities toward the neuronal lineage; (III) lymphoblastoid cell lines from CdLS patients and healthy donors restoring cellular proliferation rate and inducing the expression of CyclinD1. This work supports a role for WNT-pathway regulation of CdLS brain and behavioral abnormalities and a consistent phenotype rescue by lithium in experimental models.

The short-chain fatty acid butyrate, produced by the gut microbiota, acts as a potent histone deacetylase (HDAC) inhibitor. We assessed possible ameliorative effects of butyrate, relative to other HDAC inhibitors, in in vitro and in vivo models of Rubinstein–Taybi syndrome (RSTS), a severe neurodevelopmental disorder caused by variants in the genes encoding the histone acetyltransferases CBP and p300. In RSTS cell lines, butyrate led to the patient-specific rescue of acetylation defects at subtoxic concentrations. Remarkably, we observed that the commensal gut microbiota composition in a cohort of RSTS patients is significantly depleted in butyrate-producing bacteria compared to healthy siblings. We demonstrate that the effects of butyrate and the differences in microbiota composition are conserved in a Drosophila melanogaster mutant for CBP, enabling future dissection of the gut–host interactions in an in vivo RSTS model. This study sheds light on microbiota composition in a chromatinopathy, paving the way for novel therapeutic interventions.

The Rubinstein–Taybi syndrome (RSTS) is a rare developmental disorder characterized by craniofacial dysmorphisms, broad thumbs and toes, intellectual disability, growth deficiency, and recurrent infections. Mutations in the cyclic adenosine monophosphate response element‐binding protein (CREB)‐binding protein (CREBBP) or in the E1A‐associated protein p300 (EP300) genes have been demonstrated in 55% (RSTS1) and up to 8% of the patients (RSTS2), respectively. Dysfunction of immune response has been reported in a subgroup of individuals with RSTS. Here we characterize two patients carrying the same EP300 variant and distinctive RSTS features (including congenital heart abnormalities, short stature, feeding problems, and gastroesophageal reflux). Whole exome sequencing did not support a dual molecular diagnosis hypothesis. Nonetheless, patients showed distinct clinical manifestations and immunological features. The most severe phenotype was associated with reduced T‐cell production and diversity. This latter feature was confirmed in a control group of four RSTS patients.

Chromatinopathies (CPs) are an expanding group of rare genetic disorders affecting epigenetic machinery. Besides an intricate genotypic spectrum, these conditions share overlapping phenotypes characterized by neurocognitive impairment, growth defects and distinctive, but often convergent, facial features. Although individually rare, the landscape of CPs is increasingly growing and represents an emerging and possibly underestimated cause of disability. Due to their complexity and rarity, accurate diagnosis and management pose significant difficulties. To address these challenges and gain a deeper overview of these diseases' spectrum, we retrospectively collected clinical characteristics of 239 patients diagnosed with CPs and critically analyzed their diagnostic journey, growth charts, neurological and gestaltic features. Starting from the largest collection of CPs to date, our data point to wide sequencing analyses as the best shortcut to diagnosis. We have also demonstrated the importance of growth defects in this group of disorders that require dedicated growth tables, and we have delved into the great variability of neurological and clinical burden in these conditions. This retrospective study provides a significant advance in our understanding of these rare diseases and will help to improve diagnostic, therapeutic, and clinical approaches to CPs and to develop personalized multidisciplinary care plans for affected patients.

Background: Cellular senescence is a biological process in which the cell cycle is arrested in response to DNA damage caused by different endogenous and exogenous stimuli. In senescent cells, activation of intracellular cascade induces epigenetic, morphological and metabolic changes. Among them, senescent status is characterized by an alteration of the epigenome and the establishment of a peculiar senescence-associated secretory phenotype (SASP), which contributes to the extracellular matrix remodeling and senescence spreading. Growing interest is directed towards senescence relevance both in physiological processes and in pathological ones, including rare progeroid syndromes. However, little is known about senescence contribution to the onset and development of rare diseases in which aging traits are not manifested. Main body: Here, we review the current knowledge about senescence involvement in four rare mendelian disorders of the epigenetic machinery (i.e. chromatinopathies) and four rare lung diseases, that can be considered a paradigm for understanding how epigenome alteration and aberrant microenvironment modification in senescence process might drive disease onset and progression. First, we report the main characteristics of chromatinopathies and the relation between the chromatin-related epigenetic defects and the senescence features in Sotos syndrome, Cornelia de Lange syndrome, Rett syndrome, and Kleefstra syndromes. Thereafter, we describe the pathological alteration and senescence involvement in cystic fibrosis, idiopathic pulmonary fibrosis, pulmonary arterial hypertension and lymphangioleiomyomatosis, considering them as models of rare lung diseases in which accumulation of senescent cells and their proinflammatory SASP have a central role. Conclusion: Exploring the role of senescence in different and less common diseases might promote the understanding of the senescent process as a novel player in rare disorders, for a more comprehensive vision of their complexity and the suggestion of novel possible therapeutical targets.