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fragile X syndrome - Clinical Profile, Genes & Research | Kisho | Kisho
Fragile X syndrome (FXS) is a genetic syndrome associated with the FMR1 gene, which encodes the fragile X mental retardation 1 protein that participates in neural development. The condition is manifested through intellectual, emotional, behavioral, physical, and learning disabilities, and the packet lists the nervous system and skeletal system as affected organ systems. GeneReviews (FMR1 Disorders) groups FXS with fragile X-associated tremor/ataxia syndrome (FXTAS) and fragile X-associated primary ovarian insufficiency (FXPOI) as FMR1-related disorders. The packet places prevalence in the COMMON category, at 1 to 5 in 10,000 people, and cites a birth prevalence of 1 in 4,000 males and 1 in 8,000 females. GeneReviews describes FXS as the most common known single-gene cause of autism spectrum disorder, accounting for about 2% to 3% of cases.
Built from Human Phenotype Ontology (HPO) phenotype annotations and GeneReviews clinical descriptions. Features represent findings documented across known cases — not an exhaustive list of possible symptoms.
The packet records 24 phenotypes, with HPO frequencies for the listed features. Neurodevelopmental and behavioral features: moderate intellectual disability is listed as always present (100%), while hyperactivity, reduced eye contact, recurrent hand flapping, and self-biting are listed as frequent (30 to 79%). Curated findings also include anxiety and autism spectrum features, with intellectual disability described as moderate in males and mild in affected females. GeneReviews reports a mean IQ of 40 to 45 in males, with a range from below 10 to within the normal range, delayed motor and speech milestones, and autism spectrum disorder in 50% to 70% of individuals with FXS. Physical features: long face, mandibular prognathia, and macrotia are listed as frequent, while large forehead and metacarpophalangeal joint hyperextensibility are listed as occasional (5 to 29%). GeneReviews states that only a subset of affected individuals have typical physical features, which become more obvious with age, and that macroorchidism is identified in essentially all males after puberty. Other medical features: GeneReviews lists hypotonia, gastroesophageal reflux, strabismus, seizures, sleep disorders, joint laxity, scoliosis, and recurrent otitis media in childhood, and mitral valve prolapse and aortic root dilatation most commonly in adults. Variation: GeneReviews reports that females heterozygous for the full mutation show the same features with lower frequency and milder involvement. Premutation carriers may develop FXTAS or FXPOI according to the curated findings. GeneReviews describes FXTAS as late-onset progressive cerebellar ataxia and intention tremor, with onset typically between ages 60 and 65 years and variation among individuals.
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Genetic Landscape
Assembled from HGNC gene records, ClinGen gene-disease validity evidence, and ClinVar pathogenic variant data. Validity classifications reflect the strength of published evidence linking each gene to this disease.
Fragile X syndrome results from a CGG repeat expansion in the FMR1 gene. According to the packet's molecular mechanism, normal alleles have 5 to 44 CGG repeats, premutation alleles have 55 to 200 repeats, and full mutation alleles have more than 200 repeats, with hypermethylation silencing FMR1 expression. FMR1 carries a DEFINITIVE ClinGen validity classification in the packet and is located on the X chromosome. The recorded inheritance pattern is X-linked, and GeneReviews describes FMR1 disorders as inherited in an X-linked manner. GeneReviews states that the phenotype in males depends almost entirely on the nature of the variant, while the phenotype in females depends on both the variant and random X-chromosome inactivation. It describes all full-mutation males as having intellectual disability, and about half of full-mutation females as having intellectual disability and half as having normal intellect, which it ties to reduced penetrance in females. Premutation carriers are described as having normal intellect and appearance, although a subset may have subtle intellectual or behavioral symptoms, and GeneReviews notes it is unclear whether these result from the premutation or from ascertainment bias. Intermediate alleles of approximately 45 to 54 repeats are described as not causing FXS.
Diagnosis
Drawn from GeneReviews diagnostic guidelines, newborn screening panel status (RUSP), and ClinGen gene-disease validity classifications. Reflects current clinical evidence and consensus where available.
The packet lists FMR1 CGG repeat analysis (PCR and Southern blot), methylation status analysis, and clinical evaluation for characteristic features as diagnostic methods. GeneReviews states that the diagnosis of an FMR1 disorder is established through specialized molecular genetic testing, and that multigene panels and exome or genome sequencing are useful only when no CGG repeat expansion is detected but FXS is still suspected. A definite diagnosis of FXS typically requires a full-mutation repeat size of more than 200 CGG repeats, while diagnoses of FXTAS or FXPOI are associated with premutation-sized repeats of 55 to 200. According to GeneReviews, FMR1 disorders are considered in individuals with intellectual disability or developmental delay of unknown cause, in males with unexplained autism spectrum disorder, and in females with unexplained autism spectrum disorder plus an additional indicator, such as a compatible phenotype or a family history of X-linked neurodevelopmental disorders. GeneReviews notes that physical features are not reliable for diagnosis. The packet lists geneticists, genetic counselors, developmental pediatricians, neurologists, psychiatrists, and speech-language pathologists as relevant specialist types.
Treatment
Compiled from FDA-approved drug records, orphan drug designations, and FDA Adverse Event Reporting System (FAERS) safety data. GeneReviews management guidance is included where available.
No FDA-approved treatment for FXS is certified in this packet; orphan drug records in the packet carry DESIGNATED or WITHDRAWN status, which does not indicate approval. The packet lists foundational therapies of early intervention and special education services, speech and language therapy, occupational therapy for sensory integration, behavioral therapy for anxiety and behavioral challenges, and medications for attention, anxiety, and behavioral symptoms. GeneReviews states that no specific treatment is available and that supportive, symptom-based care is provided, typically as a dual approach of psychopharmacologic treatment of symptoms alongside therapeutic services such as behavioral intervention, speech and language therapy, occupational therapy, and individualized educational support. It describes medications used in FXS as often the same as those used in the general population, and notes that individuals with FXS are more sensitive to the adverse effects of psychotropic medications. It names the Fragile X Clinical and Research Consortium as providing evaluations and treatment guidelines.
Based on GeneReviews surveillance recommendations, HPO phenotype frequency and severity annotations, and published prevalence estimates from Orphanet and OMIM.
A natural history record is not certified in this packet. GeneReviews describes the course in terms of developmental and behavioral features: behaviors tend to evolve over time, with reduced responsiveness and activity sometimes seen before age two years, followed by increasing hyperactivity and attention-deficit/hyperactivity disorder symptoms, with anxiety and irritable behaviors emerging to varying degrees during childhood and sometimes increasing during or after puberty. Outcomes are described as varying by sex, allele type, and, in females, X-chromosome inactivation. For FXTAS, GeneReviews describes ataxia leading to gait and postural instability, with most individuals needing a walking aid within ten years of diagnosis. Life expectancy and survival data are not certified in this packet.
Research Landscape
Sourced from ClinicalTrials.gov and PubMed. Publication types are classified using NLM-curated article metadata; research type breakdowns reflect the nature of published work for this disease.
Active clinical trials for this condition are listed on ClinicalTrials.gov, and the packet records numerous active studies. Records include a recruiting Phase 2 study of MRM-3379 in male participants sponsored by Mirum Pharmaceuticals, a recruiting Phase 2 study of CTH120 sponsored by Connecta Therapeutics, a recruiting Phase 2 study of cannabidiol on anxiety and GABAergic function sponsored by Universite de Sherbrooke, and a Phase 2 open-label extension of ZYN002 sponsored by Zynerba Pharmaceuticals (active, not recruiting). The packet lists research directions of targeted treatments for core symptoms, gene reactivation strategies, and mGluR5 modulators and other pathway-specific therapies. GeneReviews describes multiple ongoing trials of medication for behavior or drugs targeting the underlying neurobiological mechanism, citing metformin and mavoglurant as examples. Many orphan drug designations are recorded for FXS, and designation alone does not indicate approval or current development.
Data assembled from 10 of 12 sources · Last updated Nov 3, 2026, 11:45 PM UTC
Diseases are connected by shared genes, phenotypes, therapeutic targets, and MONDO disease hierarchy. The Rare badge reflects Kisho's rarity classification — scored from authoritative sources including OMIM, Orphanet, orphan drug designations, clinical trial activity, and published prevalence data.
AQNEURSA is approved in the U.S. ... for the treatment of Ataxia in patients with Ataxia-Telangiectasia (A-T) based on positive Phase 3 clinical trial results. AQNEURSA is currently under review by the EMA for adult and pediatric patients diagnosed with A-T. In addition, IntraBio’s rare disease expertise ... AQNEURSA is approved in the U.S. and EU for the treatment of neurological manifestations of NPC, with commercialization well underway in the U.S. The FDA recently approved AQNEURSA for the treatment of Ataxia in patients with Ataxia-Telangiectasia (A-T) based on positive Phase 3 clinical trial results. AQNEURSA is currently under review by the EMA for adult and pediatric patients diagnosed with A-T. In addition, IntraBio’s rare disease expertise would strengthen Shionogi’s capabilities across its rare disease pipeline, including clinical programs in Pompe disease, Fragile X syndrome, and Jordan’s syndrome, as well as additional early-stage rare neurodegenerative disease programs recently added to the pipeline. The planned acquisition of IntraBio, a biopharmaceutical company specializing in the research, development, and commercialization of pharmaceuticals targeting rare neurodegenerative diseases and genetic neurological diseases, and its approved therapy, AQNEURSA, builds on that foundation. Following closing, Shionogi will be well positioned to support healthcare professionals and deliver AQNEURSA to patients who may benefit from treatment. Today in North America, our portfolio of FDA-approved products includes an antibiotic for serious infections caused by susceptible Gram-negative bacteria, an oral antiviral for post-exposure prophylaxis of COVID-19 and a therapy for amyotrophic lateral sclerosis (ALS). Our pipeline programs include investigational treatments across infectious disease, rare disease and additional high‑need therapeutic areas. 2. IntraBio Receives European Commission Approval of AQNEURSA® for the Treatment of Niemann-Pick Type C Disease · 3. FDA Approves Therapy to Treat Ataxia in Patients with Ataxia-Telangiectasia, a Rare Genetic Disorder
AQNEURSA is approved in the U.S. ... for the treatment of Ataxia in patients with Ataxia-Telangiectasia (A-T) based on positive Phase 3 clinical trial results. AQNEURSA is currently under review by the EMA for adult and pediatric patients diagnosed with A-T. In addition, IntraBio’s rare disease expertise ... AQNEURSA is approved in the U.S. and EU for the treatment of neurological manifestations of NPC, with commercialization well underway in the U.S. The FDA recently approved AQNEURSA for the treatment of Ataxia in patients with Ataxia-Telangiectasia (A-T) based on positive Phase 3 clinical trial results. AQNEURSA is currently under review by the EMA for adult and pediatric patients diagnosed with A-T. In addition, IntraBio’s rare disease expertise would strengthen Shionogi’s capabilities across its rare disease pipeline, including clinical programs in Pompe disease, Fragile X syndrome, and Jordan’s syndrome, as well as additional early-stage rare neurodegenerative disease programs recently added to the pipeline. The planned acquisition of IntraBio, a biopharmaceutical company specializing in the research, development, and commercialization of pharmaceuticals targeting rare neurodegenerative diseases and genetic neurological diseases, and its approved therapy, AQNEURSA, builds on that foundation. Following closing, Shionogi will be well positioned to support healthcare professionals and deliver AQNEURSA to patients who may benefit from treatment. Today in North America, our portfolio of FDA-approved products includes an antibiotic for serious infections caused by susceptible Gram-negative bacteria, an oral antiviral for post-exposure prophylaxis of COVID-19 and a therapy for amyotrophic lateral sclerosis (ALS). Our pipeline programs include investigational treatments across infectious disease, rare disease and additional high‑need therapeutic areas. 2. IntraBio Receives European Commission Approval of AQNEURSA® for the Treatment of Niemann-Pick Type C Disease · 3. FDA Approves Therapy to Treat Ataxia in Patients with Ataxia-Telangiectasia, a Rare Genetic Disorder
AQNEURSA is approved in the U.S. ... for the treatment of Ataxia in patients with Ataxia-Telangiectasia (A-T) based on positive Phase 3 clinical trial results. AQNEURSA is currently under review by the EMA for adult and pediatric patients diagnosed with A-T. In addition, IntraBio’s rare disease expertise ... AQNEURSA is approved in the U.S. and EU for the treatment of neurological manifestations of NPC, with commercialization well underway in the U.S. The FDA recently approved AQNEURSA for the treatment of Ataxia in patients with Ataxia-Telangiectasia (A-T) based on positive Phase 3 clinical trial results. AQNEURSA is currently under review by the EMA for adult and pediatric patients diagnosed with A-T. In addition, IntraBio’s rare disease expertise would strengthen Shionogi’s capabilities across its rare disease pipeline, including clinical programs in Pompe disease, Fragile X syndrome, and Jordan’s syndrome, as well as additional early-stage rare neurodegenerative disease programs recently added to the pipeline. The planned acquisition of IntraBio, a biopharmaceutical company specializing in the research, development, and commercialization of pharmaceuticals targeting rare neurodegenerative diseases and genetic neurological diseases, and its approved therapy, AQNEURSA, builds on that foundation. Following closing, Shionogi will be well positioned to support healthcare professionals and deliver AQNEURSA to patients who may benefit from treatment. Today in North America, our portfolio of FDA-approved products includes an antibiotic for serious infections caused by susceptible Gram-negative bacteria, an oral antiviral for post-exposure prophylaxis of COVID-19 and a therapy for amyotrophic lateral sclerosis (ALS). Our pipeline programs include investigational treatments across infectious disease, rare disease and additional high‑need therapeutic areas. 2. IntraBio Receives European Commission Approval of AQNEURSA® for the Treatment of Niemann-Pick Type C Disease · 3. FDA Approves Therapy to Treat Ataxia in Patients with Ataxia-Telangiectasia, a Rare Genetic Disorder
CONNECTA Therapeutics secures €3.1M to advance CTH120, a TrkB modulator, into mid-stage trials for Fragile X syndrome. This funding will support the development of a treatment for a rare neurodevelopmental disorder with no approved therapies.
The National Fragile X Foundation and CONNECTA Therapeutics discuss the challenges and opportunities in developing therapies for fragile X syndrome. Key topics include trial endpoints and the need for neuroplasticity modulation to advance treatment options.
