Beckwith Weidemann syndrome: a behavioral phenotype-genotype study

Genome-wide screening reveals essential roles for HOX genes and imprinted genes during caudal neurogenesis of human embryonic stem cells

Mapping the essential pathways for neuronal differentiation can uncover new therapeutics and models for neurodevelopmental disorders. We thus utilized a genome-wide loss-of-function library in haploid human embryonic stem cells, differentiated into caudal neuronal cells. We show that essential genes for caudal neurogenesis are enriched for secreted and membrane proteins and that a large group of neurological conditions, including neurodegenerative disorders, manifest early neuronal phenotypes. Furthermore, essential transcription factors are enriched with homeobox (HOX) genes demonstrating synergistic regulation and surprising non-redundant functions between HOXA6 and HOXB6 paralogs. Moreover, we establish the essentialome of imprinted genes during neurogenesis, demonstrating that maternally expressed genes are non-essential in pluripotent cells and their differentiated germ layers, yet several are essential for neuronal development. These include Beckwith-Wiedemann syndrome- and Angelman syndrome-related genes, for which we suggest a novel regulatory pathway. Overall, our work identifies essential pathways for caudal neuronal differentiation and stage-specific phenotypes of neurological disorders.

Cognitive, Social, and Emotional-Behavioral Outcomes in Children and Adolescents With Beckwith-Wiedemann Syndrome

Although Beckwith-Wiedemann syndrome spectrum (BWSp) is not usually associated with intellectual disability, recent evidences calls for further investigation of cognitive development and academic skills in children with BWSp. Moreover, research has documented social difficulties and emotional-behavioral problems associated with BWSp. Nevertheless, a full characterization of socio-emotional development in BWSp is still lacking. In the current study, cognitive and socio-emotional development was assessed in 29 children with BWSp aged 5-18 years, using a test of nonverbal intelligence, a neuropsychological battery covering multiple domains, academic skills tests, and questionnaires evaluating autistic traits and emotional-behavioral problems. As expected, most participants showed adequate performance in cognitive tests. However, the findings also highlighted greater difficulties in language than visuospatial processing, strengths in social perception, as well as slowness in reading and mental calculation. The assessment of emotional-behavioral difficulties indicated a prevalent phenotype characterized by increased anxiety, low self-esteem, social withdrawal and a tendency to control externalizing reactions, but no associations with autistic traits, cognitive outcomes, and the clinical score proposed by the recent Consensus statement. Increased social perception and internalization problems likely result from coping strategies with social and care-related stress. Overall, the findings of this study inform clinical management and genetic counseling for children and adolescents with BWSp.

Five years of experience in the Epigenetics and Chromatin Clinic: what have we learned and where do we go from here?

The multidisciplinary Epigenetics and Chromatin Clinic at Johns Hopkins provides comprehensive medical care for individuals with rare disorders that involve disrupted epigenetics. Initially centered on classical imprinting disorders, the focus shifted to the rapidly emerging group of genetic disorders resulting from pathogenic germline variants in epigenetic machinery genes. These are collectively called the Mendelian disorders of the epigenetic machinery (MDEMs), or more broadly, Chromatinopathies. In five years, 741 clinic visits have been completed for 432 individual patients, with 153 having confirmed epigenetic diagnoses. Of these, 115 individuals have one of 26 MDEMs with every single one exhibiting global developmental delay and/or intellectual disability. This supports prior observations that intellectual disability is the most common phenotypic feature of MDEMs. Additional common phenotypes in our clinic include growth abnormalities and neurodevelopmental issues, particularly hypotonia, attention-deficit/hyperactivity disorder (ADHD), and anxiety, with seizures and autism being less common. Overall, our patient population is representative of the broader group of MDEMs and includes mostly autosomal dominant disorders impacting writers more so than erasers, readers, and remodelers of chromatin marks. There is an increased representation of dual function components with a reader and an enzymatic domain. As expected, diagnoses were made mostly by sequencing but were aided in some cases by DNA methylation profiling. Our clinic has helped to facilitate the discovery of two new disorders, and our providers are actively developing and implementing novel therapeutic strategies for MDEMs. These data and our high follow-up rate of over 60% suggest that we are achieving our mission to diagnose, learn from, and provide optimal care for our patients with disrupted epigenetics.

Partial Glossectomy Combined With Radiofrequency Ablation for Macroglossia in Beckwith-Wiedemann Syndrome

OBJECTIVE

As the most common feature of Beckwith-Wiedemann syndrome (BWS), macroglossia may influence the quality of life, maxillofacial growth, and speech development of children. The retrospective study aimed to investigate the therapeutic effect of partial glossectomy combined with radiofrequency ablation (RFA) for macroglossia patients in BWS.

METHODS

A retrospective study was conducted in BWS-derived macroglossia patients who underwent partial glossectomy combined with RFA from May 2019 to January 2021. In total, 35 patients consisting of 17 males and 18 females met the inclusion criteria and underwent surgery by the same plastic surgeon. Demographic characteristics, BWS features, operation details, preoperative and postoperative outcomes, satisfaction evaluations, and subgroup analysis were collected and assessed.

RESULTS

Of the 35 patients involved, the average age at the time of surgery was 14.05±8.08 months, and the average surgery duration was 48.17±6.72 minutes. Only 1 patient suffered ventral tongue wound dehiscence, and the rest of the patients did not develop any other complications. The severity and frequency of tongue protrusion, drooling, snoring, and feeding difficulty were significantly ameliorated. The patient's parents showed satisfaction towards the overall surgery, tongue's appearance, and tongue's motor function. Tongue's height decreased from 32.09±1.16 mm before the operation to 29.29±1.33 mm after the operation.

CONCLUSION

The partial glossectomy combined RFA exerts a safe, effective and viable technique to treat BWS-derived macroglossia.

Evidence for parent-of-origin effects in autism spectrum disorder: a narrative review

Autism spectrum disorder (ASD) is a heterogeneous group of early-onset neurodevelopmental disorders known to be highly heritable with a complex genetic architecture. Abnormal brain developmental trajectories that impact synaptic functioning, excitation-inhibition balance and brain connectivity are now understood to play a central role in ASD. Ongoing efforts to identify the genetic underpinnings still prove challenging, in part due to phenotypic and genetic heterogeneity.This review focuses on parent-of-origin effects (POEs), where the phenotypic effect of an allele depends on its parental origin. POEs include genomic imprinting, transgenerational effects, mitochondrial DNA, sex chromosomes and mutational transmission bias. The motivation for investigating these mechanisms in ASD has been driven by their known impacts on early brain development and brain functioning, in particular for the most well-documented POE, genomic imprinting. Moreover, imprinting is implicated in syndromes such as Angelman and Prader-Willi, which frequently share comorbid symptoms with ASD. In addition to other regions in the genome, this comprehensive review highlights the 15q11-q13 and 7q chromosomal regions as well as the mitochondrial DNA as harbouring the majority of currently identified POEs in ASD.

Psychosocial Difficulties in Preschool-Age Children with Beckwith–Wiedemann Syndrome: An Exploratory Study

Beckwith–Wiedemann syndrome (BWS) is a rare overgrowth disease and is not usually associated with intellectual delay. Living with a chronic illness condition such as BWS, however, might affect emotional-behavioral functioning and psychosocial development. To investigate this issue, parents of 30 children with BWS between 1.5 and 6 years old compiled standardized questionnaires assessing the presence of emotional-behavioral and developmental problems. The group mean scores in each scale of behavioral problems fell within the average range. Nevertheless, 23% of the sample presented scores beyond the risk threshold for social withdrawal. As regards psychomotor development, a lower mean score was reliable in the social domain compared to other developmental scales, and in the gross-motor compared to fine-motor functions. Moreover, scores in the at-risk band were reliable in almost half of the children for social development. Notably, older age was overall associated with higher emotional-behavioral and developmental difficulties, while no other socio-demographic or clinical variables accounted for the scores obtained in the questionnaires. These findings ask for a wider consideration by health and educational professionals of the psychosocial functioning of children with BWS, so as to early detect at-risk conditions and eventually promote adequate interventions.

Mental Health, Mitochondria, and the Battle of the Sexes

This paper presents a broad perspective on how mental disease relates to the different evolutionary strategies of men and women and to growth, metabolism, and mitochondria—the enslaved bacteria in our cells that enable it all. Several mental disorders strike one sex more than the other; yet what truly matters, regardless of one’s sex, is how much one’s brain is “female” and how much it is “male”. This appears to be the result of an arms race between the parents over how many resources their child ought to extract from the mother, hence whether it should grow a lot or stay small and undemanding. An uneven battle alters the child’s risk of developing not only insulin resistance, diabetes, or cancer, but a mental disease as well. Maternal supremacy increases the odds of a psychosis-spectrum disorder; paternal supremacy, those of an autism-spectrum one. And a particularly lopsided struggle may invite one or the other of a series of syndromes that come in pairs, with diametrically opposite, excessively “male” or “female” characteristics. By providing the means for this tug of war, mitochondria take center stage in steadying or upsetting the precarious balance on which our mental health is built.

Deep exploration of a CDKN1C mutation causing a mixture of Beckwith-Wiedemann and IMAGe syndromes revealed a novel transcript associated with developmental delay

Background

Loss-of-function mutations in CDKN1C cause overgrowth, that is, Beckwith-Wiedemann syndrome (BWS), while gain-of-function variants in the gene’s PCNA binding motif cause a growth-restricted condition called IMAGe syndrome. We report on a boy with a remarkable mixture of both syndromes, with developmental delay and microcephaly as additional features.

Methods

Whole-exome DNA sequencing and ultra-deep RNA sequencing of leucocyte-derived and fibroblast-derived mRNA were performed in the family.

Results

We found a maternally inherited variant in the IMAGe hotspot region: NM_000076.2(CDKN1C) c.822_826delinsGAGCTG. The asymptomatic mother had inherited this variant from her mosaic father with mild BWS features. This delins caused tissue-specific frameshifting resulting in at least three novel mRNA transcripts in the boy. First, a splice product causing CDKN1C truncation was the likely cause of BWS. Second, an alternative splice product in fibroblasts encoded IMAGe-associated amino acid substitutions. Third, we speculate that developmental delay is caused by a change in the alternative CDKN1C-201 (ENST00000380725.1) transcript, encoding a novel isoform we call D (UniProtKB: A6NK88). Isoform D is distinguished from isoforms A and B by alternative splicing within exon 1 that changes the reading frame of the last coding exon. Remarkably, this delins changed the reading frame back to the isoform A/B type, resulting in a hybrid D–A/B isoform.

Conclusion

Three different cell-type-dependent RNA products can explain the co-occurrence of both BWS and IMAGe features in the boy. Possibly, brain expression of hybrid isoform D–A/B is the cause of developmental delay and microcephaly, a phenotypic feature not previously reported in CDKN1C patients.

Special Therapy and Psychosocial Needs Identified in a Multidisciplinary Cancer Predisposition Syndrome Clinic

Identification of patients with cancer predisposition syndromes (CPSs) can provide vital information to guide care of an existing cancer, survey for future malignancy, and counsel families. The same underlying mutation responsible for a CPS may also result in other phenotypic abnormalities amenable to therapeutic intervention. The purpose of this study was to examine patients followed in our multidisciplinary CPS clinic to determine the prevalence and scope of medical and psychosocial needs. Data from a baseline evaluation of a single-center patient registry was reviewed. Eligible patients included those with a known or suspected CPS. Over 3 years, 73 patients consented and had successful follow-up. Utilization rate of special therapies, defined as speech therapy, occupational therapy, and/or physical therapy, in the CPS population was 50.7%, significantly higher than a representative sample of children with special needs. Prevalence of 504/IEP (Individualized Education Program) utilization was 20.5%. Patients with CPSs have a high prevalence of medical and psychosocial needs beyond their risk for cancer, for which early screening for necessary interventions should be offered to maximize the patient's developmental potential. Future research is needed to further define the developmental and cognitive phenotypes of these syndromes, and to evaluate the effectiveness of subsequent interventions.

Diagnosis and Management of Beckwith-Wiedemann Syndrome

Beckwith-Wiedemann syndrome (BWS) is a human genomic imprinting disorder that presents with a wide spectrum of clinical features including overgrowth, abdominal wall defects, macroglossia, neonatal hypoglycemia, and predisposition to embryonal tumors. It is associated with genetic and epigenetic changes on the chromosome 11p15 region, which includes two imprinting control regions. Here we review strategies for diagnosing and managing BWS and delineate commonly used genetic tests to establish a molecular diagnosis of BWS. Recommended first-line testing assesses DNA methylation and copy number variation of the BWS region. Tissue mosaicism can occur in patients with BWS, posing a challenge for genetic testing, and a negative test result does not exclude a diagnosis of BWS. Further testing should analyze additional tissue samples or employ techniques with higher diagnostic yield. Identifying the BWS molecular subtype is valuable for coordinating patient care because of the (epi)genotype-phenotype correlations, including different risks and types of embryonal tumors.

Corpus Callosum Abnormalities and Short Femurs in Beckwith-Wiedemann Syndrome: A Report of Two Fetal Cases

INTRODUCTION

Beckwith-Wiedemann syndrome (BWS) is the most common overgrowth syndrome. Clinical features are highly variable, including occasional posterior fossa malformations but no femoral shortening.

CASE REPORT

We report two fetuses with BWS associated with short femurs and corpus callosum hypoplasia. Case 2 was growth restricted. BWS was confirmed by molecular studies showing a loss of methylation at ICR2 at 11p15 chromosomic region in case 1 and a gain of methylation at ICR1 and a loss of methylation at ICR2 locus in case 2.

CONCLUSION

Although the phenotype and the genotype of BWS is now well-known, the presence of corpus callosum abnormalities and short femurs expand the phenotypic spectrum of the disorder.

Expert consensus document: Clinical and molecular diagnosis, screening and management of Beckwith-Wiedemann syndrome: an international consensus statement

Beckwith-Wiedemann syndrome (BWS), a human genomic imprinting disorder, is characterized by phenotypic variability that might include overgrowth, macroglossia, abdominal wall defects, neonatal hypoglycaemia, lateralized overgrowth and predisposition to embryonal tumours. Delineation of the molecular defects within the imprinted 11p15.5 region can predict familial recurrence risks and the risk (and type) of embryonal tumour. Despite recent advances in knowledge, there is marked heterogeneity in clinical diagnostic criteria and care. As detailed in this Consensus Statement, an international consensus group agreed upon 72 recommendations for the clinical and molecular diagnosis and management of BWS, including comprehensive protocols for the molecular investigation, care and treatment of patients from the prenatal period to adulthood. The consensus recommendations apply to patients with Beckwith-Wiedemann spectrum (BWSp), covering classical BWS without a molecular diagnosis and BWS-related phenotypes with an 11p15.5 molecular anomaly. Although the consensus group recommends a tumour surveillance programme targeted by molecular subgroups, surveillance might differ according to the local health-care system (for example, in the United States), and the results of targeted and universal surveillance should be evaluated prospectively. International collaboration, including a prospective audit of the results of implementing these consensus recommendations, is required to expand the evidence base for the design of optimum care pathways.

Role of Genetics in the Etiology of Autistic Spectrum Disorder: Towards a Hierarchical Diagnostic Strategy

Progress in epidemiological, molecular and clinical genetics with the development of new techniques has improved knowledge on genetic syndromes associated with autism spectrum disorder (ASD). The objective of this article is to show the diversity of genetic disorders associated with ASD (based on an extensive review of single-gene disorders, copy number variants, and other chromosomal disorders), and consequently to propose a hierarchical diagnostic strategy with a stepwise evaluation, helping general practitioners/pediatricians and child psychiatrists to collaborate with geneticists and neuropediatricians, in order to search for genetic disorders associated with ASD. The first step is a clinical investigation involving: (i) a child psychiatric and psychological evaluation confirming autism diagnosis from different observational sources and assessing autism severity; (ii) a neuropediatric evaluation examining neurological symptoms and developmental milestones; and (iii) a genetic evaluation searching for dysmorphic features and malformations. The second step involves laboratory and if necessary neuroimaging and EEG studies oriented by clinical results based on clinical genetic and neuropediatric examinations. The identification of genetic disorders associated with ASD has practical implications for diagnostic strategies, early detection or prevention of co-morbidity, specific treatment and follow up, and genetic counseling.

Reframing autism as a behavioral syndrome and not a specific mental disorder: Implications of genetic and phenotypic heterogeneity

Clinical and molecular genetics have advanced current knowledge on genetic disorders associated with autism. A review of diverse genetic disorders associated with autism is presented and for the first time discussed extensively with regard to possible common underlying mechanisms leading to a similar cognitive-behavioral phenotype of autism. The possible role of interactions between genetic and environmental factors, including epigenetic mechanisms, is in particular examined. Finally, the pertinence of distinguishing non-syndromic autism (isolated autism) from syndromic autism (autism associated with genetic disorders) will be reconsidered. Given the high genetic and etiological heterogeneity of autism, autism can be viewed as a behavioral syndrome related to known genetic disorders (syndromic autism) or currently unknown disorders (apparent non-syndromic autism), rather than a specific categorical mental disorder. It highlights the need to study autism phenotype and developmental trajectory through a multidimensional, non-categorical approach with multivariate analyses within autism spectrum disorder but also across mental disorders, and to conduct systematically clinical genetic examination searching for genetic disorders in all individuals (children but also adults) with autism.

Humans as Superorganisms: How Microbes, Viruses, Imprinted Genes, and Other Selfish Entities Shape Our Behavior

Psychologists and psychiatrists tend to be little aware that (a) microbes in our brains and guts are capable of altering our behavior; (b) viral DNA that was incorporated into our DNA millions of years ago is implicated in mental disorders; (c) many of us carry the cells of another human in our brains; and (d) under the regulation of viruslike elements, the paternally inherited and maternally inherited copies of some genes compete for domination in the offspring, on whom they have opposite physical and behavioral effects. This article provides a broad overview, aimed at a wide readership, of the consequences of our coexistence with these selfish entities. The overarching message is that we are not unitary individuals but superorganisms, built out of both human and nonhuman elements; it is their interaction that determines who we are.

Assessment and causes of stridor

Stridor is a variably pitched respiratory sound, caused by abnormal air passage during breathing and often is the most prominent sign of upper airway obstruction. It is usually heard on inspiration (typically resulting from supraglottic or glottic obstruction) but also can occur on expiration (originating from obstruction at or below glottic level and/or severe upper airway obstruction). Stridor due to congenital anomalies may exist from birth or may develop within days, weeks or months. Various congenital and acquired disorders prevail in neonates, infants, children, and adolescents, and have to be distinguished. History, age of the child and physical examination together often allow a presumptive diagnosis. Further investigations may be necessary to establish a definite diagnosis, and flexible airway endoscopy is the diagnostic procedure of choice in most circumstances ("stridor is visible").

Recommendations of the Scientific Committee of the Italian Beckwith-Wiedemann Syndrome Association on the diagnosis, management and follow-up of the syndrome

Beckwith-Wiedemann syndrome (BWS) is the most common (epi)genetic overgrowth-cancer predisposition disorder. Given the absence of consensual recommendations or international guidelines, the Scientific Committee of the Italian BWS Association (www.aibws.org) proposed these recommendations for the diagnosis, molecular testing, clinical management, follow-up and tumor surveillance of patients with BWS. The recommendations are intended to allow a timely and appropriate diagnosis of the disorder, to assist patients and their families, to provide clinicians and caregivers optimal strategies for an adequate and satisfactory care, aiming also at standardizing clinical practice as a national uniform approach. They also highlight the direction of future research studies in this setting. With recent advances in understanding the disease (epi)genetic mechanisms and in describing large cohorts of BWS patients, the natural history of the disease will be dissected. In the era of personalized medicine, the emergence of specific (epi)genotype-phenotype correlations in BWS will likely lead to differentiated follow-up approaches for the molecular subgroups, to the development of novel tools to evaluate the likelihood of cancer development and to the refinement and optimization of current tumor screening strategies.

CONCLUSIONS

In this article, we provide the first comprehensive recommendations on the complex management of patients with Beckwith-Wiedemann syndrome.

MECP2 Is a Frequently Amplified Oncogene with a Novel Epigenetic Mechanism That Mimics the Role of Activated RAS in Malignancy

An unbiased genome-scale screen for unmutated genes that drive cancer growth when overexpressed identified methyl cytosine-guanine dinucleotide (CpG) binding protein 2 (MECP2) as a novel oncogene. MECP2 resides in a region of the X-chromosome that is significantly amplified across 18% of cancers, and many cancer cell lines have amplified, overexpressed MECP2 and are dependent on MECP2 expression for growth. MECP2 copy-number gain and RAS family member alterations are mutually exclusive in several cancer types. The MECP2 splicing isoforms activate the major growth factor pathways targeted by activated RAS, the MAPK and PI3K pathways. MECP2 rescued the growth of a KRAS(G12C)-addicted cell line after KRAS downregulation, and activated KRAS rescues the growth of an MECP2-addicted cell line after MECP2 downregulation. MECP2 binding to the epigenetic modification 5-hydroxymethylcytosine is required for efficient transformation. These observations suggest that MECP2 is a commonly amplified oncogene with an unusual epigenetic mode of action.

SIGNIFICANCE

MECP2 is a commonly amplified oncogene in human malignancies with a unique epigenetic mechanism of action. Cancer Discov; 6(1); 45-58. ©2015 AACR.This article is highlighted in the In This Issue feature, p. 1.

Comorbidity of intellectual disability confounds ascertainment of autism: implications for genetic diagnosis

While recent studies suggest a converging role for genetic factors towards risk for nosologically distinct disorders including autism, intellectual disability (ID), and epilepsy, current estimates of autism prevalence fail to take into account the impact of comorbidity of these disorders on autism diagnosis. We aimed to assess the effect of comorbidity on the diagnosis and prevalence of autism by analyzing 11 years (2000-2010) of special education enrollment data on approximately 6.2 million children per year. We found a 331% increase in the prevalence of autism from 2000 to 2010 within special education, potentially due to a diagnostic recategorization from frequently comorbid features such as ID. The decrease in ID prevalence equaled an average of 64.2% of the increase of autism prevalence for children aged 3-18 years. The proportion of ID cases potentially undergoing recategorization to autism was higher (P = 0.007) among older children (75%) than younger children (48%). Some US states showed significant negative correlations between the prevalence of autism compared to that of ID while others did not, suggesting state-specific health policy to be a major factor in categorizing autism. Further, a high frequency of autistic features was observed when individuals with classically defined genetic syndromes were evaluated for autism using standardized instruments. Our results suggest that current ascertainment practices are based on a single facet of autism-specific clinical features and do not consider associated comorbidities that may confound diagnosis. Longitudinal studies with detailed phenotyping and deep molecular genetic analyses are necessary to completely understand the cause of this complex disorder.

(Epi)genotype-phenotype correlations in Beckwith-Wiedemann syndrome: a paradigm for genomic medicine

Beckwith-Wiedemann syndrome (BWS) is the commonest overgrowth cancer predisposition disorder and represents a model for human imprinting dysregulation and tumorigenesis. BWS features can variably combine and present a widely variable range of severity in the phenotypic expression. This wide spectrum is paralleled at molecular level by complex (epi)genetic defects on chromosome 11p15.5 leading to disrupted expression of imprinted genes controlling growth and cellular proliferation. In this review, we outline the spectrum of clinical manifestations of BWS analyzing their (epi)genotype-phenotype correlations. The differences observed in the phenotypic profiles of BWS molecular subtypes allow a composite view of this syndrome with implications on clinical care, diagnosis, follow-up, and management, and provide directions for future disease monitoring.

Expression of imprinted genes in placenta is associated with infant neurobehavioral development

Genomic imprinting disorders often exhibit delayed neurobehavioral development, suggesting this unique mechanism of epigenetic regulation plays a role in mental and neurological health. While major errors in imprinting have been linked to adverse health outcomes, there has been little research conducted on how moderate variability in imprinted gene expression within a population contributes to differences in neurobehavioral outcomes, particularly at birth. Here, we profiled the expression of 108 known and putative imprinted genes in human placenta samples from 615 infants assessed by the Neonatal Intensive Care Unit (NICU) Network Neurobehavioral Scales (NNNS). Data reduction identified 10 genes (DLX5, DHCR24, VTRNA2-1, PHLDA2, NPAP1, FAM50B, GNAS-AS1, PAX8-AS1, SHANK2, and COPG2IT1) whose expression could distinguish between newborn neurobehavioral profiles derived from the NNNS. Clustering infants based on the expression pattern of these genes identified 2 groups of infants characterized by reduced quality of movement, increased signs of asymmetrical and non-optimal reflexes, and increased odds of demonstrating increased signs of physiologic stress and abstinence. Overall, these results suggest that common variation in placental imprinted gene expression is linked to suboptimal performance on scales of neurological functioning as well as with increased signs of physiologic stress, highlighting the central importance of the control of expression of these genes in the placenta for neurobehavioral development.

Opposite risk patterns for autism and schizophrenia are associated with normal variation in birth size: phenotypic support for hypothesized diametric gene-dosage effects

Opposite phenotypic and behavioural traits associated with copy number variation and disruptions to imprinted genes with parent-of-origin effects have led to the hypothesis that autism and schizophrenia share molecular risk factors and pathogenic mechanisms, but a direct phenotypic comparison of how their risks covary has not been attempted. Here, we use health registry data collected on Denmark's roughly 5 million residents between 1978 and 2009 to detect opposing risks of autism and schizophrenia depending on normal variation (mean ± 1 s.d.) in adjusted birth size, which we use as a proxy for diametric gene-dosage variation in utero. Above-average-sized babies (weight, 3691-4090 g; length, 52.8-54.3 cm) had significantly higher risk for autism spectrum (AS) and significantly lower risk for schizophrenia spectrum (SS) disorders. By contrast, below-average-sized babies (2891-3290 g; 49.7-51.2 cm) had significantly lower risk for AS and significantly higher risk for SS disorders. This is the first study directly comparing autism and schizophrenia risks in the same population, and provides the first large-scale empirical support for the hypothesis that diametric gene-dosage effects contribute to these disorders. Only the kinship theory of genomic imprinting predicts the opposing risk patterns that we discovered, suggesting that molecular research on mental disease risk would benefit from considering evolutionary theory.

Meningocele in a congolese female with beckwith-wiedemann phenotype

Beckwith-Wiedemann syndrome (BWS) is a rare congenital syndrome characterized by an overgrowth, macroglossia, exomphalos, and predisposition to embryonal tumors. Central nervous abnormalities associated with BWS are rare. We describe a one-day-old Congolese female who presented meningocele associated with BWS phenotype.

Gene × Environment interactions in autism spectrum disorders: role of epigenetic mechanisms

Several studies support currently the hypothesis that autism etiology is based on a polygenic and epistatic model. However, despite advances in epidemiological, molecular and clinical genetics, the genetic risk factors remain difficult to identify, with the exception of a few chromosomal disorders and several single gene disorders associated with an increased risk for autism. Furthermore, several studies suggest a role of environmental factors in autism spectrum disorders (ASD). First, arguments for a genetic contribution to autism, based on updated family and twin studies, are examined. Second, a review of possible prenatal, perinatal, and postnatal environmental risk factors for ASD are presented. Then, the hypotheses are discussed concerning the underlying mechanisms related to a role of environmental factors in the development of ASD in association with genetic factors. In particular, epigenetics as a candidate biological mechanism for gene × environment interactions is considered and the possible role of epigenetic mechanisms reported in genetic disorders associated with ASD is discussed. Furthermore, the example of in utero exposure to valproate provides a good illustration of epigenetic mechanisms involved in ASD and innovative therapeutic strategies. Epigenetic remodeling by environmental factors opens new perspectives for a better understanding, prevention, and early therapeutic intervention of ASD.

Clinical neurogenetics: autism spectrum disorders

Autism spectrum disorders are neurodevelopmental disorders characterized by deficits in social interactions, communication, and repetitive or restricted interests. There is strong evidence that de novo or inherited genetic alterations play a critical role in causing Autism Spectrum Disorders, but non-genetic causes, such as in utero infections, may also play a role. Magnetic resonance imaging based and autopsy studies indicate that early rapid increase in brain size during infancy could underlie the deficits in a large subset of subjects. Clinical studies show benefits for both behavioral and pharmacological treatment strategies. Genotype-specific treatments have the potential for improving outcome in the future.

Non-coding RNAs in chromatin disease involving neurological defects

Novel classes of small and long non-coding RNAs (ncRNAs) are increasingly becoming apparent, being engaged in diverse structural, functional and regulatory activities. They take part in target gene silencing, play roles in transcriptional, post-transcriptional and epigenetic processes, such as chromatin remodeling, nuclear reorganization with the formation of silent compartments and fine-tuning of gene recruitment into them. Among their functions, non-coding RNAs are thought to act either as guide or scaffold for epigenetic modifiers that write, erase, and read the epigenetic signature over the genome. Studies on human disorders caused by defects in epigenetic modifiers and involving neurological phenotypes highlight the disruption of diverse classes of non-coding RNAs. Noteworthy, these molecules mediate a wide spectrum of neuronal functions, including brain development, and synaptic plasticity. These findings imply a significant contribution of ncRNAs in pathophysiology of the aforesaid diseases and provide new concepts for potential therapeutic applications.

Autism spectrum disorders: the quest for genetic syndromes

Autism spectrum disorders (ASD) are a heterogeneous group of neurodevelopmental disabilities with various etiologies, but with a heritability estimate of more than 90%. Although the strong correlation between autism and genetic factors has been long established, the exact genetic background of ASD remains unclear. A number of genetic syndromes manifest ASD at higher than expected frequencies compared to the general population. These syndromes account for more than 10% of all ASD cases and include tuberous sclerosis, fragile X, Down, neurofibromatosis, Angelman, Prader-Willi, Williams, Duchenne, etc. Clinicians are increasingly required to recognize genetic disorders in individuals with ASD, in terms of providing proper care and prognosis to the patient, as well as genetic counseling to the family. Vice versa, it is equally essential to identify ASD in patients with genetic syndromes, in order to ensure correct management and appropriate educational placement. During investigation of genetic syndromes, a number of issues emerge: impact of intellectual disability in ASD diagnoses, identification of autistic subphenotypes and differences from idiopathic autism, validity of assessment tools designed for idiopathic autism, possible mechanisms for the association with ASD, etc. Findings from the study of genetic syndromes are incorporated into the ongoing research on autism etiology and pathogenesis; different syndromes converge upon common biological backgrounds (such as disrupted molecular pathways and brain circuitries), which probably account for their comorbidity with autism. This review paper critically examines the prevalence and characteristics of the main genetic syndromes, as well as the possible mechanisms for their association with ASD.

The evolutionary paradox and the missing heritability of schizophrenia

Schizophrenia is one of the most detrimental common psychiatric disorders, occurring at a prevalence of approximately 1%, and characterized by increased mortality and reduced reproduction, especially in men. The heritability has been estimated around 70% and the genome-wide association meta-analyses conducted by the Psychiatric Genomics Consortium have been successful at identifying an increasing number of risk loci. Various theories have been proposed to explain why genetic variants that predispose to schizophrenia persist in the population, despite the fitness reduction in affected individuals, a question known as the evolutionary paradox. In this review, we consider evolutionary perspectives of schizophrenia and of the empirical evidence that may support these perspectives. Proposed evolutionary explanations include balancing selection, fitness trade-offs, fluctuating environments, sexual selection, mutation-selection balance and genomic conflicts. We address the expectations about the genetic architecture of schizophrenia that are predicted by different evolutionary scenarios and discuss the implications for genetic studies. Several potential sources of "missing" heritability, including gene-environment interactions, epigenetic variation, and rare genetic variation are examined from an evolutionary perspective. A better understanding of evolutionary history may provide valuable clues to the genetic architecture of schizophrenia and other psychiatric disorders, which is highly relevant to genetic studies that aim to detect genetic risk variants.

Human-specific regulation of MeCP2 levels in fetal brains by microRNA miR-483-5p

Proper neurological function in humans requires precise control of levels of the epigenetic regulator methyl CpG-binding protein 2 (MeCP2). MeCP2 protein levels are low in fetal brains, where the predominant MECP2 transcripts have an unusually long 3' untranslated region (UTR). Here, we show that miR-483-5p, an intragenic microRNA of the imprinted IGF2, regulates MeCP2 levels through a human-specific binding site in the MECP2 long 3' UTR. We demonstrate the inverse correlation of miR-483-5p and MeCP2 levels in developing human brains and fibroblasts from Beckwith-Wiedemann syndrome patients. Importantly, expression of miR-483-5p rescues abnormal dendritic spine phenotype of neurons overexpressing human MeCP2. In addition, miR-483-5p modulates the levels of proteins of the MeCP2-interacting corepressor complexes, including HDAC4 and TBL1X. These data provide insight into the role of miR-483-5p in regulating the levels of MeCP2 and interacting proteins during human fetal development.

Macrocephaly as a clinical indicator of genetic subtypes in autism

An association between autism and macrocephaly has been previously described. A subset of cases with extreme macrocephaly (>3 standard deviation [SD], 99.7th percentile) have been correlated to mutations in the gene phosphatase and tensin homolog (PTEN). However, the phenotypic and genetic characterization of the remaining cases remains unclear. We report the phenotypic classification and genetic testing evaluation of a cohort of 33 patients with autism and macrocephaly. Within our cohort, we confirm the association of PTEN mutations and extreme macrocephaly (>3 SD, 99.7th percentile) and identify mutations in 22% of cases, including three novel PTEN mutations. In addition, we define three phenotypic subgroups: (a) those cases associated with somatic overgrowth, (b) those with disproportionate macrocephaly, and (c) those with relative macrocephaly. We have devised a novel way to segregate patients into these subgroups that will aide in the stratification of autism macrocephaly cases. Within these subgroups, we further expand the genetic etiologies for autism cases with macrocephaly by describing two novel suspected pathogenic copy number variants located at 6q23.2 and 10q24.32. These findings demonstrate the phenotypic heterogeneity of autism cases associated with macrocephaly and their genetic etiologies. The clinical yield from PTEN mutation analysis is 22% and 9% from chromosomal microarray (CMA) testing within this cohort. The identification of three distinct phenotypic subgroups within macrocephaly autism patients may allow for the identification of their respective distinct genetic etiologies that to date have remained elusive.

Cellular functions of genetically imprinted genes in human and mouse as annotated in the gene ontology

By analyzing the cellular functions of genetically imprinted genes as annotated in the Gene Ontology for human and mouse, we found that imprinted genes are often involved in developmental, transport and regulatory processes. In the human, paternally expressed genes are enriched in GO terms related to the development of organs and of anatomical structures. In the mouse, maternally expressed genes regulate cation transport as well as G-protein signaling processes. Furthermore, we investigated if imprinted genes are regulated by common transcription factors. We identified 25 TF families that showed an enrichment of binding sites in the set of imprinted genes in human and 40 TF families in mouse. In general, maternally and paternally expressed genes are not regulated by different transcription factors. The genes Nnat, Klf14, Blcap, Gnas and Ube3a contribute most to the enrichment of TF families. In the mouse, genes that are maternally expressed in placenta are enriched for AP1 binding sites. In the human, we found that these genes possessed binding sites for both, AP1 and SP1.

Diametric gene-dosage effects as windows into neurogenetic architecture

Gene expression can be modulated in two opposite directions, towards higher or lower amounts of product. How do diametric changes in gene dosage influence neurological development and function? Recent studies of transgenic and knockout mouse models, genomic copy-number variants, imprinted-gene expression alterations, and sex-chromosome aneuploidies are revealing examples of 'mirror-extreme' brain and behavior phenotypes, which provide unique insights into neurodevelopmental architecture. These convergent studies quantitatively connect gene dosages with specific trajectories and outcomes, with important implications for the experimental dissection of normal neurological functions, the genetic analysis of psychiatric disorders, the development of pharmacological therapies, and mechanisms for the evolution of human brain and behavior.

The molecular basis of cognitive deficits in pervasive developmental disorders

Persons with pervasive developmental disorders (PDD) exhibit a range of cognitive deficits that hamper their quality of life, including difficulties involving communication, sociability, and perspective-taking. In recent years, a variety of studies in mice that model genetic syndromes with a high risk of PDD have provided insights into the underlying molecular mechanisms associated with these disorders. What is less appreciated is how the molecular anomalies affect neuronal and circuit function to give rise to the cognitive deficits associated with PDD. In this review, we describe genetic mutations that cause PDD and discuss how they alter fundamental social and cognitive processes. We then describe efforts to correct cognitive impairments associated with these disorders and identify areas of further inquiry in the search for molecular targets for therapeutics for PDD.

Epigenetic influences that modulate infant growth, development, and disease

SIGNIFICANCE

Epigenetic modifications are key processes in understanding normal human development and are largely responsible for the myriad cell and tissue types that originate from a single-celled fertilized ovum. The three most common processes involved in bringing about epigenetic changes are DNA methylation, histone modification, and miRNA effects. There are critical periods in the development of the zygote, the embryo, and the fetus where in the organism is most susceptible to epigenetic influences because of normal demethylation and de novo methylation processes that occur in the womb.

RECENT ADVANCES

A number of epigenetic modifications of normal growth patterns have been recognized, leading to altered development and disease states in the mammalian fetus and infant. 'Fetal programming' due to these epigenetic changes has been implicated in pathogenesis of adult-onset disease such as hypertension, diabetes, and cardiovascular disease. There may also be transgenerational effects of such epigenetic modifications.

CRITICAL ISSUES

The impact of environmental agents and endogenous factors such as stress at critical periods of infant development has immediate, life-long and even multi-generational effects. Both the timing and the degree of insult may be important. Understanding these influences may help prevent onset of disease and promote normal growth.

FUTURE DIRECTIONS

Use of one-carbon metabolism modifying agents such as folic acid during critical periods of epigenetic modulation may have significant clinical impact. Their use as therapeutic agents in targeted epigenetic modulation of genes may be the new frontier for clinical therapeutics.

Placenta-imprinted gene expression association of infant neurobehavior

OBJECTIVE

To identify links between altered gene imprinting in the placenta and infant neurobehavioral profiles.

STUDY DESIGN

Quantitative reverse-transcription polymerase chain reaction was used to examine the expression of 22 imprinted candidate genes in a series of 106 term human primary placenta tissues. The expression pattern uncovered was associated with Neonatal Intensive Care Unit Network Neurobehavioral Scales summary scores in the corresponding infants. Clustering of the expression data was used to define distinct classes of expression.

RESULTS

Significant associations were identified between classes of expression and the Neonatal Intensive Care Unit Network Neurobehavioral Scales quality of movement (P = .02) and handling (P = .006) scores. Multivariate regression demonstrated an independent effect of imprinted gene expression profile on these neurobehavioral scores after controlling for confounders.

CONCLUSION

These results suggest that alterations in imprinted gene expression in the placenta are associated with infant neurodevelopmental outcomes, and suggest a role for the placenta and genomic imprinting in the placenta beyond intrauterine growth regulation.

The imprinted brain: how genes set the balance between autism and psychosis

The imprinted brain theory proposes that autism spectrum disorder (ASD) represents a paternal bias in the expression of imprinted genes. This is reflected in a preference for mechanistic cognition and in the corresponding mentalistic deficits symptomatic of ASD. Psychotic spectrum disorder (PSD) would correspondingly result from an imbalance in favor of maternal and/or X-chromosome gene expression. If differences in gene expression were reflected locally in the human brain as mouse models and other evidence suggests they are, ASD would represent not so much an 'extreme male brain' as an extreme paternal one, with PSD correspondingly representing an extreme maternal brain. To the extent that copy number variation resembles imprinting and aneuploidy in nullifying or multiplying the expression of particular genes, it has been found to conform to the diametric model of mental illness peculiar to the imprinted brain theory. The fact that nongenetic factors such as nutrition in pregnancy can mimic and/or interact with imprinted gene expression suggests that the theory might even be able to explain the notable effect of maternal starvation on the risk of PSD - not to mention the 'autism epidemic' of modern affluent societies. Finally, the theory suggests that normality represents balanced cognition, and that genius is an extraordinary extension of cognitive configuration in both mentalistic and mechanistic directions. Were it to be proven correct, the imprinted brain theory would represent one of the biggest single advances in our understanding of the mind and of mental illness that has ever taken place, and would revolutionize psychiatric diagnosis, prevention and treatment - not to mention our understanding of epigenomics.

Autistic regression in a child with Silver-Russell syndrome and maternal UPD 7

Silver-Russell syndrome (SRS) is a heterogeneous syndrome which is characterized by severe intrauterine and postnatal growth retardation and typical dysmorphic features. In 5-10% of SRS patients, a maternal uniparental disomy of chromosome 7 (UPD7) can be detected. We describe a 4.5-y old boy. Physical examination at the age of 4.5 y was remarkable for small stature, relatively big head, triangular face, broad forehead, pointed chin and clinodactyly. He had hypopigmented macules on his back with no evidence of asymmetry/hemihypertrophy. Clinical diagnosis of Silver-Russell syndrome was made. Maternal UPD of chromosome 7 was found, confirming the diagnosis. Along with the clinical findings that are described in this syndrome he had moderate developmental delay which is not commonly found in these patients and underwent an autistic regression around the age of 2 years. This association has only once been described before in this syndrome. A possible explanation is that the autism is not a part of SRS but is due to the UPD. Our case suggests an association of autistic regression with a locus on chromosome 7.

Autism and cancer risk

A literature review was conducted on the genetic and developmental bases of autism in relation to genes and pathways associated with cancer risk. Convergent lines of evidence from four types of analysis: (1) recent theoretical studies on the causes of autism, (2) epidemiological studies, (3) genetic analyses linking autism with mutations in tumor suppressor genes and other cancer-associated genes and pathways, and (4) contrasts with schizophrenia, Parkinson's, and Alzheimer's disease indicate that autism may involve altered cancer risk. This evidence should motivate further epidemiological studies, and it provides useful insights into the nature of the genetic, epigenetic, and environmental factors underlying the etiologies of autism, other neurological conditions, and carcinogenesis.

Pathology from evolutionary conflict, with a theory of X chromosome versus autosome conflict over sexually antagonistic traits

Evolutionary conflicts cause opponents to push increasingly hard and in opposite directions on the regulation of traits. One can see only the intermediate outcome from the balance of the exaggerated and opposed forces. Intermediate expression hides the underlying conflict, potentially misleading one to conclude that trait regulation is designed to achieve efficient and robust expression, rather than arising by the precarious resolution of conflict. Perturbation often reveals the underlying nature of evolutionary conflict. Upon mutation or knockout of one side in the conflict, the other previously hidden and exaggerated push on the trait may cause extreme, pathological expression. In this regard, pathology reveals hidden evolutionary design. We first review several evolutionary conflicts between males and females, including conflicts over mating, fertilization, and the growth rate of offspring. Perturbations of these conflicts lead to infertility, misregulated growth, cancer, behavioral abnormalities, and psychiatric diseases. We then turn to antagonism between the sexes over traits present in both males and females. For many traits, the different sexes favor different phenotypic values, and constraints prevent completely distinct expression in the sexes. In this case of sexual antagonism, we present a theory of conflict between X-linked genes and autosomal genes. We suggest that dysregulation of the exaggerated conflicting forces between the X chromosome and the autosomes may be associated with various pathologies caused by extreme expression along the male-female axis. Rapid evolution of conflicting X-linked and autosomal genes may cause divergence between populations and speciation.

Reduced transcript expression of genes affected by inherited and de novo CNVs in autism

Individuals with autism are more likely to carry rare inherited and de novo copy number variants (CNVs). However, further research is needed to establish which CNVs are causal and the mechanisms by which these CNVs influence autism. We examined genomic DNA of children with autism (N = 41) and healthy controls (N = 367) for rare CNVs using a high-resolution array comparative genomic hybridization platform. We show that individuals with autism are more likely to harbor rare CNVs as small as ∼ 10 kb, a threshold not previously detectable, and that CNVs in cases disproportionately affect genes involved in transcription, nervous system development, and receptor activity. We also show that a subset of genes that have known or suspected allele-specific or imprinting effects and are within rare-case CNVs may undergo loss of transcript expression. In particular, expression of CNTNAP2 and ZNF214 are decreased in probands compared with their unaffected transmitting parents. Furthermore, expression of PRODH and ARID1B, two genes affected by de novo CNVs, are decreased in probands compared with controls. These results suggest that for some genes affected by CNVs in autism, reduced transcript expression may be a mechanism of pathogenesis during neurodevelopment.

Etiological heterogeneity in autism spectrum disorders: more than 100 genetic and genomic disorders and still counting

There is increasing evidence that autism spectrum disorders (ASDs) can arise from rare highly penetrant mutations and genomic imbalances. The rare nature of these variants, and the often differing orbits of clinical and research geneticists, can make it difficult to fully appreciate the extent to which we have made progress in understanding the genetic etiology of autism. In fact, there is a persistent view in the autism research community that there are only a modest number of autism loci known. We carried out an exhaustive review of the clinical genetics and research genetics literature in an attempt to collate all genes and recurrent genomic imbalances that have been implicated in the etiology of ASD. We provide data on 103 disease genes and 44 genomic loci reported in subjects with ASD or autistic behavior. These genes and loci have all been causally implicated in intellectual disability, indicating that these two neurodevelopmental disorders share common genetic bases. A genetic overlap between ASD and epilepsy is also apparent in many cases. Taken together, these findings clearly show that autism is not a single clinical entity but a behavioral manifestation of tens or perhaps hundreds of genetic and genomic disorders. Increased recognition of the etiological heterogeneity of ASD will greatly expand the number of target genes for neurobiological investigations and thereby provide additional avenues for the development of pathway-based pharmacotherapy. Finally, the data provide strong support for high-resolution DNA microarrays as well as whole-exome and whole-genome sequencing as critical approaches for identifying the genetic causes of ASDs.

The origins and evolution of genetic disease risk in modern humans

Patterns and risks of human disease have evolved. In this article, I review evidence regarding the importance of recent adaptive evolution, positive selection, and genomic conflicts in shaping the genetic and phenotypic architectures of polygenic human diseases. Strong recent selection in human populations can create and maintain genetically based disease risk primarily through three processes: increased scope for dysregulation from recent human adaptations, divergent optima generated by intraspecific genomic conflicts, and transient or stable deleterious by-products of positive selection caused by antagonistic pleiotropy, ultimately due to trade-offs at the levels of molecular genetics, development, and physiology. Human disease due to these processes appears to be concentrated in three sets of phenotypes: cognition and emotion, reproductive traits, and life-history traits related to long life-span. Diverse, convergent lines of evidence suggest that a small set of tissues whose pleiotropic patterns of gene function and expression are under especially strong selection-brain, placenta, testis, prostate, breast, and ovary-has mediated a considerable proportion of disease risk in modern humans.

Autism spectrum disorders and epigenetics

OBJECTIVE

Current research suggests that the causes of autism spectrum disorders (ASD) are multifactorial and include both genetic and environmental factors. Several lines of evidence suggest that epigenetics also plays an important role in ASD etiology and that it might, in fact, integrate genetic and environmental influences to dysregulate neurodevelopmental processes. The objective of this review is to illustrate how epigenetic modifications that are known to alter gene expression without changing primary DNA sequence may play a role in the etiology of ASD.

METHOD

In this review, we summarize current knowledge about epigenetic modifications to genes and genomic regions possibly involved in the etiology of ASD.

RESULTS

Several genetic syndromes comorbid with ASD, which include Rett, Fragile X, Prader-Willi, Angelman, and CHARGE (Coloboma of the eye, Heart defects, Atresia of the nasal choanae, Retardation of growth and/or development, Genital and/or urinary abnormalities, and Ear abnormalities and deafness), all demonstrate dysregulation of epigenetic marks or epigenetic mechanisms. We report also on genes or genomic regions exhibiting abnormal epigenetic regulation in association with either syndromic (15q11-13 maternal duplication) or nonsyndromic forms of ASD. Finally, we discuss the state of current knowledge regarding the etiologic role of environmental factors linked to both the development of ASD and epigenetic dysregulation.

CONCLUSION

Data reviewed in this article highlight a variety of situations in which epigenetic dysregulation is associated with the development of ASD, thereby supporting a role for epigenetics in the multifactorial etiologies of ASD.

Addition of H19 'loss of methylation testing' for Beckwith-Wiedemann syndrome (BWS) increases the diagnostic yield

Beckwith-Wiedemann syndrome (BWS) is a clinical diagnosis; however, molecular confirmation via abnormal methylation of DMR2(LIT1) and/or DMR1(H19) has clinical utility due to epigenotype-tumor association. Despite the strong link between H19 hypermethylation and tumor risk, several diagnostic laboratories only test for hypomethylation of LIT1. We assessed the added diagnostic value of combined LIT1 and H19 testing in a large series of referred samples from 1298 patients, including 53 well-characterized patients from the St. Louis Children's Hospital BWS-Registry (validation samples) and 1245 consecutive nationwide referrals (practice samples). Methylation-sensitive enzymatic digestion with Southern hybridization assessed loss of normal imprinting. In the validation group, abnormal LIT1 hypomethylation was detected in 60% (32/52) of patients but LIT1/H19-combined testing was abnormal in 68% (36/53); sensitivity in the practice setting demonstrated 27% (342/1245) abnormal LIT1 and 32% (404/1245) abnormal LIT1/H19-combined. In addition, H19 methylation was abnormal in 7% of LIT1-normal patients. We observed absence of uniparental disomy (UPD) in 27% of combined LIT1/H19-abnormal samples, diagnostic of multilocus methylation abnormalities; in contrast to studies implicating that combined LIT1/H19 abnormalities are diagnostic of UPD. The overall low detection rate, even in validated patient samples and despite characterization of both loci and UPD status, emphasizes the importance of clinical diagnosis in BWS.

Genetic causes of syndromic and non-syndromic autism

AIMS

Over the past decade, genetic tests have become available for numerous heritable disorders, especially those whose inheritance follows the Mendelian model. Autism spectrum disorders (ASDs) represent a group of developmental disorders with a strong genetic basis. During the past few years, genetic research in ASDs has been successful in identifying several vulnerability loci and a few cytogenetic abnormalities or single-base mutations implicated in the causation of autism.

METHOD

In this study the literature was reviewed to highlight genotype-phenotype correlations between causal gene mutations or cytogenetic abnormalities and behavioural or morphological phenotypes.

RESULTS

Based on this knowledge, practical information is offered to help clinicians pursue targeted genetic testing of individuals with autism whose clinical phenotype is suggestive of a specific genetic or genomic aetiology.

INTERPRETATION

Comprehensive research into the molecular mechanism of autism is required to aid the development of disease-specific targeted therapies. In order to transfer this recently acquired knowledge into clinical practice, it is critical to define a set of phenotypic inclusion criteria that must be met by affected probands to justify their enrolment in a specific genetic testing programme.