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We describe the phenotype of 22 male patients (20 probands) carrying a hemizygous missense variant in MED12. The phenotypic spectrum is very broad ranging from nonspecific intellectual disability (ID) to the three well-known syndromes: Opitz-Kaveggia syndrome, Lujan-Fryns syndrome, or Ohdo syndrome. The identified variants were randomly distributed throughout the gene (p = 0.993, χ 2 test), but mostly outside the functional domains (p = 0.004; χ 2 test). Statistical analyses did not show a correlation between the MED12-related phenotypes and the locations of the variants (p = 0.295; Pearson correlation), nor the protein domain involved (p = 0.422; Pearson correlation). In conclusion, establishing a genotype-phenotype correlation in MED12-related diseases remains challenging. Therefore, we think that patients with a causative MED12 variant are currently underdiagnosed due to the broad patients' clinical presentations., (© 2022 The Authors. American Journal of Medical Genetics Part A published by Wiley Periodicals LLC.)

Variants in RAC3, encoding a small GTPase RAC3 which is critical for the regulation of actin cytoskeleton and intracellular signal transduction, are associated with a rare neurodevelopmental disorder with structural brain anomalies and facial dysmorphism. We investigated a cohort of 10 unrelated participants presenting with global psychomotor delay, hypotonia, behavioural disturbances, stereotyped movements, dysmorphic features, seizures and musculoskeletal abnormalities. MRI of brain revealed a complex pattern of variable brain malformations, including callosal abnormalities, white matter thinning, grey matter heterotopia, polymicrogyria/dysgyria, brainstem anomalies and cerebellar dysplasia. These patients harboured eight distinct de novo RAC3 variants, including six novel variants (NM_005052.3): c.34G > C p.G12R, c.179G > A p.G60D, c.186_188delGGA p.E62del, c.187G > A p.D63N, c.191A > G p.Y64C and c.348G > C p.K116N. We then examined the pathophysiological significance of these novel and previously reported pathogenic variants p.P29L, p.P34R, p.A59G, p.Q61L and p.E62K. In vitro analyses revealed that all tested RAC3 variants were biochemically and biologically active to variable extent, and exhibited a spectrum of different affinities to downstream effectors including p21-activated kinase 1. We then focused on the four variants p.Q61L, p.E62del, p.D63N and p.Y64C in the Switch II region, which is essential for the biochemical activity of small GTPases and also a variation hot spot common to other Rho family genes, RAC1 and CDC42. Acute expression of the four variants in embryonic mouse brain using in utero electroporation caused defects in cortical neuron morphology and migration ending up with cluster formation during corticogenesis. Notably, defective migration by p.E62del, p.D63N and p.Y64C were rescued by a dominant negative version of p21-activated kinase 1. Our results indicate that RAC3 variants result in morphological and functional defects in cortical neurons during brain development through variant-specific mechanisms, eventually leading to heterogeneous neurodevelopmental phenotypes., (© The Author(s) 2022. Published by Oxford University Press on behalf of the Guarantors of Brain.)

Rubinstein-Taybi syndrome (RSTS) is a developmental disorder characterized by a typical face and distal limbs abnormalities, intellectual disability, and a vast number of other features. Two genes are known to cause RSTS, CREBBP in 60% and EP300 in 8-10% of clinically diagnosed cases. Both paralogs act in chromatin remodeling and encode for transcriptional co-activators interacting with >400 proteins. Up to now 26 individuals with an EP300 mutation have been published. Here, we describe the phenotype and genotype of 42 unpublished RSTS patients carrying EP300 mutations and intragenic deletions and offer an update on another 10 patients. We compare the data to 308 individuals with CREBBP mutations. We demonstrate that EP300 mutations cause a phenotype that typically resembles the classical RSTS phenotype due to CREBBP mutations to a great extent, although most facial signs are less marked with the exception of a low-hanging columella. The limb anomalies are more similar to those in CREBBP mutated individuals except for angulation of thumbs and halluces which is very uncommon in EP300 mutated individuals. The intellectual disability is variable but typically less marked whereas the microcephaly is more common. All types of mutations occur but truncating mutations and small rearrangements are most common (86%). Missense mutations in the HAT domain are associated with a classical RSTS phenotype but otherwise no genotype-phenotype correlation is detected. Pre-eclampsia occurs in 12/52 mothers of EP300 mutated individuals versus in 2/59 mothers of CREBBP mutated individuals, making pregnancy with an EP300 mutated fetus the strongest known predictor for pre-eclampsia. © 2016 Wiley Periodicals, Inc., (© 2016 Wiley Periodicals, Inc.)

In the last decade, progress made in genetics is questioning the current implicit nosological model in the Diagnostic and Statistical Manual of Mental Disorders, fourth edition, text revision (DSM-IV-TR) and the International Classification of Diseases, tenth revision. Both the categorical nature and the comorbidity detected on applying diagnostic criteria become unsustainable in the light of the genetic architecture that is emerging from studies being conducted on the genetics of mental disorders. The classical paradigms -one gene for one disease- or even a specific distinctive genetic pattern for each condition, are concepts restricted to specific cases. In this review the objective is to describe the current scenario that has arisen following the latest advances in genetics. The lines of work being traced by research both in the present and in the near future include: the identification of variations in the number of copies (both frequent and rare), indiscriminately linked to different disorders; the concurrence of multiple variants for a single disorder; the double hit phenomenon; and epigenetic modulation. The new version of the DSM, fully aware of the deficiencies in the current model, will mark a turning point that, while somewhat timid, is decidedly oriented towards incorporating a dimensional conception of mental disorders.

Introduction and Development: Angelman syndrome (AS) is characterised by severe mental retardation (MR), the absence of language, ataxia and/or tremors in the extremities and a characteristic behavioural phenotype with a happy behaviour and hyperactivity. Patients often show signs of microcephaly and convulsions. Prader-Willi syndrome (PWS) is characterised by acute hypotonia and feeding problems in the neonatal period, and triggers an uncontrollable appetite in the infant that leads to obesity. Most patients have some degree of MR, behavioural disorders and hypogonadism. Both pathologies are caused by a number of genetic mechanisms that affect the 15q11-q13 region regulated by genomic imprinting, which means that only one of the two copies of the genes in this region will be functional, depending on which parent they come from. The physical or functional absence of genes that are only expressed by the mother's chromosome 15 causes PWS and gentic anomalies which affects the UBE3A gen mother's copy causes AS., Conclusions: It is important to confirm the clinical diagnosis and to establish the genetic mechanism responsible for the two syndromes, both for their consequences as regards the prognosis and for genetic counselling; it is therefore important to draw up a diagnostic algorithm.

Introduction: In all the aetiological studies carried out on idiopathic mental retardation (MR), chromosomal abnormalities are the factor that makes the most significant contribution. The alterations are more frequent when severe MR is accompanied by a dysmorphic phenotype, but can also be found in subjects with mild MR and with few signs of dysmorphism., Development: This work reports on new genes and critical regions in syndromes with microdeletion, such as Wolf-Hirschhorn, Smith-Magenis and Sotos--which must be taken into account in the genetic diagnosis--and new microduplications like 15q11-q13, which is associated to a behavioural phenotype of autism. The application of new molecular techniques, such as fluorescent in situ hybridisation (FISH) with multiple telomere probes, MLPA (multiplex ligation-dependent probe amplification) and array-CGH (microarray based on compared genomic hybridisation), have shown the important role played by subtelomeric and interstitial rearrangements in the aetiology of MR. Subtelomeric alterations contribute to between 5 and 7% of cases of idiopathic MR, the higher proportion corresponding to deletions, one of the most common of which is deletion 1p36. Studies that evaluate the global genome in idiopathic MR detect from 7% to 20% of cases with anomalies, the interstitial type being more frequent than the subtelomeric kind., Conclusions: The application of new technologies to idiopathic MR opens up a promising new field for the diagnosis of new syndromes with submicroscopic alterations, so that a prognosis can be determined, treatment can be improved and the risk of relapse can be defined.

Introduction: Based on clinical and genetic knowledge about certain syndromes, in recent decades the concept of behavioural phenotypes has been developed in an attempt to deal with the complex relations between genes and behaviour. The model is not linear but rather each type of behaviour is determined by the interaction of different genes and modulated by environmental factors., Development and Conclusions: The aim of this review is to provide a global view concerning the concept of 'behavioural phenotypes' based on the description of the molecular mechanisms and clinical observations of some syndromes. There is clearly a need for geneticists, who work in a laboratory, and clinicians, who can offer qualitative and quantitative data about behaviour in certain genetic syndromes, to work in collaboration. For this reason this study describes the clinical instruments that make it possible to evaluate the core aspects of behaviour and hence undertake their scientific study in situations in which their genetic dysfunction is already known.

Introduction: Angelman syndrome (AS) is a genetically-based disorder that is characterised by a physical and behavioural phenotype. Additionally, it presents a number of different systemic conditions that must also be taken into account. To evaluate the symptomatic spectrum of AS, we sought the aid of families linked to AS associations by sending them a questionnaire designed to investigate the clinical characteristics of AS., Patients and Methods: The families were sent a questionnaire aimed at determining the medical and behavioural characteristics of AS. Results from 68 patients were analysed., Results: The mean age at diagnosis was 4.8 years. The first symptoms that called parents' attention were feeding problems, followed by gastroesophageal reflux and hypotonia. The mean age at which patients were capable of maintaining a sitting posture was 18 months, while autonomous walking was not achieved until 43 months. Epilepsy, which was present in 91% of cases, began with febrile seizures in 55% of patients. In this study we found that a high percentage of patients with AS have a high resistance to pain (67%), a very common symptom in Prader-Willi syndrome, but little known in AS., Conclusions: This study offers a wide array of information about the clinical spectrum of AS obtained from an extensive populational sample. Some highly prevalent clinical aspects, such as the relative insensitivity to pain, have not been reported in previous publications as a symptom that is typical of AS.

Introduction and Development: The diagnosis of autism is based on the identification of certain behavioural criteria, but there is no biological test that allows us to diagnose the disorder. Yet, a considerable number of cases of autism, estimated to be somewhere between 11 and 37%, are linked to specific syndromes that can be identified according to their clinical characteristics, or by means of some biological marker. These cases are known as syndromic autism or 'double syndromes'. There is a relation between autism and certain genetic and metabolic diseases, epilepsy, infections of the nervous system, intrauterine exposure to certain substances and perinatal pathologies., Conclusions: The aim of this review is to guide the professional in the diagnosis of autistic children in order to rationalise the process by ruling out any underlying disease or syndrome related to the autistic condition. At the same time, we stress aetiological aspects of these syndromes, which make it easier to understand the biological bases of autism.

Introduction and Development: In this study we report on the different genetic syndromes in which autism has been described as one of the possible manifestations., Conclusions: Certain genetic syndromes are providing us with extremely valuable information about the role played by genetics in autism. This is the case of the following syndromes: Angelman syndrome, Prader-Willi syndrome, 15q11-q13 duplication, fragile X syndrome, fragile X premutation, deletion of chromosome 2q, XYY syndrome, Smith-Lemli-Opitz syndrome, Apert syndrome, mutations in the ARX gene, De Lange syndrome, Smith-Magenis syndrome, Williams syndrome, Rett syndrome, Noonan syndrome, Down syndrome, velo-cardio-facial syndrome, myotonic dystrophy, Steinert disease, tuberous sclerosis, Duchenne's disease, Timothy syndrome, 10p terminal deletion, Cowden syndrome, 45,X/46,XY mosaicism, Myhre syndrome, Sotos syndrome, Cohen syndrome, Goldenhar syndrome, Joubert syndrome, Lujan-Fryns syndrome, Moebius syndrome, hypomelanosis of Ito, neurofibromatosis type 1, CHARGE syndrome and HEADD syndrome.

Fragile X chromosome was studied in 44 male and 9 female children, affected of mental retardation. In 10 males fragile X was positive. All this patients presented mild mental deficiency with and IQ from 55 to 75. Behaviour was generally hyperkinetic except one autistic boy. Most frequent dysmorphic signs were increased head circumference and prominent large ears. Family history for mental retardation was positive almost in all cases. High percentage of children with fragile X syndrome (22.7%) encountered among male patients suggest convenience of screening, for these anomaly, of all boys affected of mild mental deficiency and all those with an autistic behaviour although lacking of dysmorphic characteristics. This will allow to know more on etiology and to offer genetic counseling to families. Although study in girls was negative, authors believe it is interesting to screen fragile X because some females with border line retardation present this chromosomic anomaly.