Introduction: Nowadays, whole-exome sequencing (WES) analysis is an essential part in the diagnostic pathway of individuals with complex phenotypes when routine exams, such as array-CGH and gene panels, have proved inconclusive. However, data on the diagnostic rate of WES analysis in adult individuals, negative to first-tier tests, are lacking. This is because initiatives with the aim of diagnosing rare diseases focus mainly on pediatric unsolved cases. Case Presentation: We hereby present a 45-year-old woman with severe intellectual disability, previous psychomotor developmental delay, behavioral disorders, stereotypies, nonconvulsive epilepsy, and dysmorphisms. The proband first came to our attention when she was 4 years old (in 1982); since then, she has undergone several clinical and instrumental assessments, without reaching a genetic diagnosis. At last, through WES analysis, a novel de novo variant in SYNGAP1 was found. The clinical characteristics associated with SYNGAP1 are similar to those presented by the proband. Conclusion: The variant is predicted to be deleterious and is most probably the cause of the proband’s phenotype. The perseverance of the clinicians and the family allowed us to reach a diagnosis in a woman with a more than 30-year history of clinical evaluations, instrumental assessments, and genetic tests. This diagnosis was of significant relevance in genetic counseling for family members and the proband herself.

Developmental regression, characterized by the loss of acquired milestones, occurs in some individuals with neurodevelopmental disorders (NDDs); yet, its molecular basis remains unclear. Studies suggest that DNA damage repair (DDR) genes, such as FAN1, may protect against neurological dysfunction by modulating the somatic stability of short tandem repeats (STRs). This study explores the contribution of DDR gene variants in NDD cases presenting with regression. We analyzed 1087 NDD patients, focusing on those carrying variants in DDR genes and presenting regression. We assessed the sensitivity to DNA damage using mitomycin C on lymphoblastoid cells. Somatic variants and STR expansions were evaluated through high-depth short-read genome sequencing. To further investigate the pathogenetic role of STR expansions, we performed long-read genome sequencing on the most severely affected proband. Probands with regression carried multiple DDR gene variants, several within the Fanconi anemia pathway. Their lymphoblastoid cells showed increased sensitivity to mitomycin C-induced cytotoxicity compared with parental and control samples. Probands with severe phenotypes and regression exhibited an accumulation of somatic variants and STR instability, enriched in neurodevelopmental genes. Our findings suggest that polygenic DDR gene variants may contribute to developmental regression in NDDs by promoting the accumulation of somatic variants and STR expansions.

Background/Objectives: The neurotransmitter glycine is involved in several physiological and pathological conditions in the Central Nervous System. Different biological structures, including glycine receptors and transporters, are under study as targets for potential drugs acting against serious neurological and psychiatric disorders. The regulation of glycine release from nerve terminals is only partially understood. We report here preliminary evidence of the modulation of glycine release through presynaptic metabotropic glutamate receptors 1 (mGlu1) from glycinergic nerve terminals in mouse hippocampi. Methods: Purified mouse hippocampal synaptosomes labeled with [³H]glycine were used to study glycine release under superfusion conditions. Results: The group I metabotropic glutamate receptor agonist 3,5-DHPG potentiated depolarization-evoked [³H]glycine release from hippocampal synaptosomes, an effect strongly counteracted by the selective mGlu1 antagonist LY 367385. 3,5-DHPG failed to increase [³H]glycine release in Grm1^crv4/crv4 mice, a mouse model lacking mGlu1. Although further research is needed to clarify these mechanisms, data suggest that glycine-releasing hippocampal nerve terminals are endowed with presynaptic mGlu1 receptors whose activation potentiates glycine release. Conclusions: Considering that in the hippocampus, glycine is relevant as a co-agonist of glutamate at NMDA receptors and that mGlu1 receptor ligands are under study as potential drugs, we propose that the possible effects of these agents on the release of glycine should be considered when studying these compounds.

Over the last few decades, scientists' attention has shifted from neuronal to non-neuronal cells to explain the mechanisms at the basis of neurodegenerative disorders, including amyotrophic lateral sclerosis (ALS). ALS is a multifactorial and multicellular disease in which microglia have a central role, during disease progression. We previously demonstrated that metabotropic glutamate receptor 5 (mGluR5) is dysfunctional in the spinal cord of the SOD1^G93A ALS mice, and its in-vivo genetic or pharmacological dampening ameliorates disease outcome and astrocyte and microglia reactivity. Here, we studied the expression of typical phenotype-related markers during the disease progression in spinal cord microglia cells acutely isolated from early asymptomatic and late symptomatic SOD1^G93A ALS mice. Moreover, we investigated whether reducing mGluR5 affected the microglia phenotype and function. In contrast to what we previously observed in astrocytes, mGluR5 expression decreased during disease progression in microglia acutely isolated from adult SOD1^G93A mice. In-vivo genetic mGluR5 downregulation did not affect microglia phenotype-relevant markers, which evidenced a unique expression distribution. Conversely, mGluR5 reduction ameliorated redox balance and bioenergetics of adult microglia. Microglia cultured from the spinal cord of SOD1^G93A pups showed that in-vitro mGluR5 pharmacological manipulation by the negative allosteric modulator CTEP partially modified their bioenergetic and oxidative status. Overall, our results suggest that mGluR5 manipulation ameliorates microglia phenotype and function in ALS by both direct and indirect mechanisms. Consequently, we hypothesised that the improvement of microglia reactive status by in-vivo mGluR5 downregulation or CTEP pharmacological modulation is supported by ameliorated bioenergetic metabolism, and the indirect astrocyte's phenotype change that promotes an improvement of the surrounding environment.