Autism spectrum disorder in the fragile X premutation state: possible mechanisms and implications

Autism-related traits in myotonic dystrophy type 1 model mice are due to MBNL sequestration and RNA mis-splicing of autism-risk genes

Genome-wide enrichment of gene-specific tandem repeat expansions has been linked to autism spectrum disorder. One such mutation is the CTG tandem repeat expansion in the 3' untranslated region of the DMPK gene, which is known to cause myotonic muscular dystrophy type 1. Although there is a clear clinical association between autism and myotonic dystrophy, the molecular basis for this connection remains unknown. Here, we report that sequestration of MBNL splicing factors by mutant DMPK RNAs with expanded CUG repeats alters the RNA splicing patterns of autism-risk genes during brain development, particularly a class of autism-relevant microexons. We demonstrate that both DMPK-CTG expansion and Mbnl null mouse models recapitulate autism-relevant mis-splicing profiles, along with social behavioral deficits and altered responses to novelty. These findings support our model that myotonic dystrophy-associated autism arises from developmental mis-splicing of autism-risk genes.

Premutation Females with preFXTAS

Fragile-X-associated tremor/ataxia syndrome (FXTAS) is a progressive neurodegenerative disorder associated with the FMR1 gene premutation, characterized by the presence of 55 to 200 CGG triplet repeat expansions. Although the initial symptoms of FXTAS typically manifest in males around the age of 60 with motor symptoms and cognitive deficits, the presentation and progression in females differ. Women, in fact, exhibit a higher prevalence of neuropsychiatric symptoms, with an earlier onset compared to the motor symptoms observed in men. The following article reports on ten cases of women with a diagnosis of FMR1 gene premutation, originating from two medical centers. All the women in the study exhibited neuropsychiatric symptoms and subtle neurological signs as common features. Symptoms typically observed in the male population, such as tremors and cerebellar ataxia, were either absent or significantly reduced in the female cohort. Conversely, there was a higher prevalence of neuropsychiatric symptoms among the women. Neurocognitive impairment was only minimally evident, with mild executive dysfunction and memory complaints noted in a subset of cases. For this reason, we propose the terminology preFXTAS or prodromic FXTAS to define a clinical presentation in women characterized by early manifestations of FXTAS that do not entirely fulfill the established diagnostic criteria but exhibit MRI evidence of white matter alterations suggesting the initiation of the disease process. The study underscores the importance of establishing new diagnostic criteria for FXTAS and, at the same time, developing new biomarkers and interview checklists/assessment scales dedicated to females.

25 years into research with the Méhes Scale, a comprehensive scale of modern dysmorphology

It has been recognized that subtle, cosmetically insignificant anomalies tend to occur cumulatively in diseases with neurodevelopmental origin. These visible signs of morphogenesis errors are called minor physical anomalies (MPAs), serving as sensitive external markers of abnormal neurodevelopment. After the introduction of the Waldrop Scale, the studies conducted on MPAs in diseases with neurodevelopmental origin gave conflicting results. It has been debated that this discrepancy can be - at least partly - attributed to the use of the Waldrop Scale. Understanding the need of a comprehensive scale of MPAs that also differentiates according to the time of development, Hungarian pediatrician professor of University of Pécs, Károly Méhes developed a scale with 57 items, the only scale differentiating minor malformations from phenogenetic variants. With the use of the Méhes Scale, our research group has been investigating the role of abnormal neurodevelopment in different neuropsychiatric and neurologic disorders since 1997. 25 years into our research, in this review we summarize the results of our 18 research articles on MPAs in different diseases. We have found an increased number of MPAs, especially in the head and mouth region, in patients with schizophrenia, bipolar disorder, Tourette syndrome, autism and many epilepsy syndromes, fortifying the role of abnormal neurodevelopment in these diseases. Moreover, an increased number of MPAs was detected among the first-degree relatives of patients with schizophrenia and bipolar I disorder, supporting the hypothesis about MPAs being endophenotypic trait markers.

Adaptive, behavioral, and cognitive outcomes in individuals with fragile X syndrome with varying autism severity

This study aimed to determine the association between severity of autism spectrum disorder (ASD) and cognitive, behavioral, and molecular measures in individuals with fragile X syndrome (FXS). Study inclusion criteria included individuals with FXS and (1) age 6-40 years, (2) full-scale IQ < 84, and (3) language ≥3-word phrases. ASD symptom severity was determined by Autism Diagnostic Observation Schedule-2 (ADOS-2). Other measures identified non-verbal IQ, adaptive skills, and aberrant behaviors. Molecular measures included blood FMR1 and CYFIP1 mRNA levels, FMRP and MMP9 levels. Analysis of variance (ANOVA) and Spearman's correlations were used to compare ASD severity groups. Data from 54 individuals was included with no/mild (N = 7), moderate (N = 18), and severe (N = 29) ASD. Individuals with high ASD severity had lower adaptive behavior scores (47.48 ± 17.49) than the no/mild group (69.00 ± 20.45, p = 0.0366); they also had more challenging behaviors, lethargy, and stereotypic behaviors. CYFIP1 mRNA expression levels positively correlated with the ADOS-2 comparison score(r2  = 0.33, p = 0.0349), with no significant correlations with other molecular markers. In conclusion, autism symptom severity is associated with more adverse cognitive and adaptive skills and specific behaviors in FXS, whereas CYFIP1 mRNA expression levels may be a potential biomarker for severity of ASD in FXS.

Screening for Fragile X Syndrome Among Filipino Children with Autism Spectrum Disorder

Individuals with autism spectrum disorder present with difficulties in social communication, restricted interests or behaviors and other co-morbidities. About 2 to 10% of cases of autism have a genetic cause, and Fragile X Syndrome (FXS) is reported in 0 to 6.5% of individuals with autism. However, the FXS and premutation prevalence among Filipino children has never been reported. The aim of the study was to establish the presence of FXS or premutation carriers among Filipino children with autism and to describe the phenotypic characteristic of cases identified. Blood was collected from 235 children aged 2-6 years old and diagnosed with autism. Samples were analyzed using PCR methods to amplify CGG repeats in the FMRI gene. The diagnosis of autism was confirmed through the Autism Diagnostic Observation Schedule-2. Additional characteristics were documented from a physical examination, Griffiths Scales of Child Development assessment and a parent-answered questionnaire using the Vineland Adaptive Behavior Scale. Fragile X testing through PCR methods in 235 children with diagnosed autism showed 220 (93.6%) were negative, no full mutations, 1 (0.436%) premutation carrier and 14 (5.95%) cases contained intermediate alleles. The FXS testing was limited to confirmed cases of autism, which is considered a high-risk group and does not provide prevalence for the general Filipino population. Subjects were self-referred or referred by clinicians, which may not represent the Filipino autism population with a bias towards those with means for clinical consultations and ability to travel to the place of testing. Samples were not measured for mosaicism, DNA methylation or AGG interspersion patterns. These may have effects on the CGG repeat expansion and overall presentation of FXS. Findings from a single premutation carrier cannot characterize features distinctly present in Filipinos with the mutation. Nevertheless, these results support the data that the prevalence of FXS in Asian populations may be lower than non-Asian populations. This can contribute to a better understanding of FXS and genetic causes of autism in the Philippines and other Asian populations.

Insight and Recommendations for Fragile X-Premutation-Associated Conditions from the Fifth International Conference on FMR1 Premutation

The premutation of the fragile X messenger ribonucleoprotein 1 (FMR1) gene is characterized by an expansion of the CGG trinucleotide repeats (55 to 200 CGGs) in the 5' untranslated region and increased levels of FMR1 mRNA. Molecular mechanisms leading to fragile X-premutation-associated conditions (FXPAC) include cotranscriptional R-loop formations, FMR1 mRNA toxicity through both RNA gelation into nuclear foci and sequestration of various CGG-repeat-binding proteins, and the repeat-associated non-AUG (RAN)-initiated translation of potentially toxic proteins. Such molecular mechanisms contribute to subsequent consequences, including mitochondrial dysfunction and neuronal death. Clinically, premutation carriers may exhibit a wide range of symptoms and phenotypes. Any of the problems associated with the premutation can appropriately be called FXPAC. Fragile X-associated tremor/ataxia syndrome (FXTAS), fragile X-associated primary ovarian insufficiency (FXPOI), and fragile X-associated neuropsychiatric disorders (FXAND) can fall under FXPAC. Understanding the molecular and clinical aspects of the premutation of the FMR1 gene is crucial for the accurate diagnosis, genetic counseling, and appropriate management of affected individuals and families. This paper summarizes all the known problems associated with the premutation and documents the presentations and discussions that occurred at the International Premutation Conference, which took place in New Zealand in 2023.

The Fragile X Protein Family in Amyotrophic Lateral Sclerosis

The fragile X protein (FXP) family comprises the multifunctional RNA-binding proteins FMR1, FXR1, and FXR2 that play an important role in RNA metabolism and regulation of translation, but also in DNA damage and cellular stress responses, mitochondrial organization, and more. FMR1 is well known for its implication in neurodevelopmental diseases. Recent evidence suggests substantial contribution of this protein family to amyotrophic lateral sclerosis (ALS) pathogenesis. ALS is a highly heterogeneous neurodegenerative disease with multiple genetic and unclear environmental causes and very limited treatment options. The loss of motoneurons in ALS is still poorly understood, especially because pathogenic mechanisms are often restricted to patients with mutations in specific causative genes. Identification of converging disease mechanisms evident in most patients and suitable for therapeutic intervention is therefore of high importance. Recently, deregulation of the FXPs has been linked to pathogenic processes in different types of ALS. Strikingly, in many cases, available data points towards loss of expression and/or function of the FXPs early in the disease, or even at the presymptomatic state. In this review, we briefly introduce the FXPs and summarize available data about these proteins in ALS. This includes their relation to TDP-43, FUS, and ALS-related miRNAs, as well as their possible contribution to pathogenic protein aggregation and defective RNA editing. Furthermore, open questions that need to be addressed before definitively judging suitability of these proteins as novel therapeutic targets are discussed.

Fragile X-Associated Neuropsychiatric Disorders (FXAND) in Young Fragile X Premutation Carriers

Background: The fragile X premutation carrier state (PM) (55-200 CGG repeats in the fragile X messenger ribonucleoprotein 1, FMR1 gene) is associated with several conditions, including fragile X-associated primary ovarian insufficiency (FXPOI) and fragile X-associated tremor ataxia (FXTAS), with current literature largely primarily investigating older PM individuals. The aim of this study was to identify the prevalence of fragile X-associated neurodevelopmental disorders (FXAND) in a sample of young PM individuals. Methods: This was a retrospective study conducted through a medical record review of PM individuals who were seen either for clinical concerns (probands, 45.9%) or identified through the cascade testing (non-probands, 54.1%) of an affected sibling with fragile X syndrome. Information on the presence of autism spectrum disorder, attention deficit hyperactivity disorder, anxiety, depression, long-term psychiatric medication intake, and cognitive function, based on standardized assessments, was obtained. Molecular data, including CGG repeat number and FMR1 mRNA levels, were also available for a subset of participants. Analysis included descriptive statistics and a test of comparison to describe the clinical profile of PM individuals pertinent to FXAND. Results: Participants included 61 individuals (52 males and 9 females) aged 7.8 to 20.0 years (mean 12.6 ± 3.4) with a mean full-scale IQ of 90.9 ± 22.7. The majority (N = 52; 85.2%) had at least one mental health disorder, with anxiety being the most common (82.0% of subjects), followed by ADHD (66.5%), and ASD (32.8%). Twenty-seven (87.1%) of non-probands also had at least one mental health condition, with probands having lower cognitive and adaptive skills than non-probands. ASD was present in 20 participants (17/52 males and 3/9 females; 15 probands) with significantly lower FSIQ in those with ASD (mean 73.5 vs. 98.0, p < 0.001). Participants with ASD had a higher number of long-term medications compared to those without (2.32 vs. 1.3, p = 0.002). Conclusions: Our findings indicate a high rate of FXAND diagnoses within a cohort of young PM individuals, including those identified via cascade testing, although this was not a population sample. An awareness of the entity of FXAND and the early recognition of the symptoms of associated conditions may facilitate timely and appropriate care for PM individuals.