{
  "schemaVersion": 2,
  "eyebrow": "Medical Genetics",
  "title": "Fragile X Syndrome",
  "summary": "Confirm suspected fragile X syndrome with dedicated FMR1 CGG-repeat and methylation testing, distinguish full mutation from premutation states, and use the result to direct developmental care, symptom-targeted treatment, and cascade reproductive counseling.",
  "seoDescription": "Physician guide to diagnosing fragile X syndrome with FMR1 testing, interpreting CGG repeats, managing comorbidities, and providing family counseling.",
  "clinicalQuestion": "How should physicians confirm fragile X syndrome, interpret FMR1 results, and organize longitudinal management and family counseling?",
  "specialty": "Medical Genetics",
  "audience": "U.S. physicians and medical trainees",
  "tags": [
    "fragile X syndrome",
    "FMR1",
    "CGG repeat expansion",
    "FMR1 premutation",
    "FXTAS",
    "FXPOI",
    "developmental delay",
    "genetic counseling"
  ],
  "keyTakeaways": [
    "Order targeted FMR1 CGG-repeat expansion testing, with methylation assessment when needed, rather than relying on exome, genome, or typical multigene panel testing to detect fragile X syndrome. [19]",
    "A full mutation is defined by more than 200 CGG repeats and is usually methylated; this establishes fragile X syndrome in the appropriate clinical setting. [19]",
    "A premutation of approximately 55-200 CGG repeats does not establish fragile X syndrome but identifies risk for fragile X-associated tremor/ataxia syndrome and, in females, fragile X-associated primary ovarian insufficiency. [19][23]",
    "Mosaic repeat size or methylation can modify phenotype and should be considered when clinical function appears discordant with repeat size alone. [19]",
    "After molecular confirmation, prioritize developmental and behavioral intervention, assess treatable ADHD, anxiety, aggression, sleep disturbance, and seizures, and provide family-centered genetic counseling. [8][11][12][14]"
  ],
  "sections": [
    {
      "id": "when-to-test",
      "eyebrow": "Diagnostic trigger",
      "heading": "Order targeted FMR1 testing when the phenotype or pedigree is suggestive",
      "intro": "Testing should resolve a specific FMR1-related diagnostic or reproductive question.",
      "paragraphs": [
        "Order dedicated FMR1 molecular testing for unexplained developmental delay, intellectual disability, autism-spectrum features, or a family history compatible with fragile X syndrome or another FMR1-related disorder. Males may have substantial developmental delay before recognizable physical features emerge; females may have milder developmental impairment. [15]",
        "Do not use a negative routine multigene panel, exome, or genome result to exclude fragile X syndrome. These approaches are useful when no CGG-repeat expansion is detected but clinical suspicion persists, whereas FMR1 disorders require specialized molecular testing for the CGG expansion. [19]",
        "In an adult with intention tremor, gait ataxia, or a family history of FMR1 expansion, distinguish fragile X-associated tremor/ataxia syndrome from full-mutation fragile X syndrome by FMR1 repeat category. In a woman with ovarian insufficiency or reproductive counseling needs, determine whether a premutation is present because premutation status is associated with fragile X-associated primary ovarian insufficiency. [19][15]"
      ],
      "bullets": [
        "Use FMR1-specific CGG-repeat expansion testing as the first molecular test when fragile X syndrome is suspected. [19]",
        "Obtain a three-generation pedigree that includes intellectual disability, autism-spectrum diagnoses, tremor/ataxia, ovarian insufficiency, and known FMR1 results. FMR1-related disorders include fragile X syndrome, fragile X-associated tremor/ataxia syndrome, and fragile X-associated primary ovarian insufficiency. [15][19]",
        "Refer confirmed or suspected expansion carriers for genetic counseling before reproductive decisions; maternal premutation alleles can expand to full mutations during intergenerational transmission. [18][22]"
      ],
      "subsections": [],
      "table": {
        "caption": "FMR1 CGG-repeat categories and the clinical decision they support. [19][23]",
        "columns": [
          "FMR1 result",
          "Interpretation",
          "Clinical next step"
        ],
        "rows": [
          [
            "Normal: 5-44 CGG repeats",
            "Does not indicate fragile X syndrome or increased transmission risk for fragile X syndrome. [23]",
            "Pursue alternative etiologies if the phenotype remains unexplained. [19]"
          ],
          [
            "Intermediate: 45-54 CGG repeats",
            "Does not establish fragile X syndrome and is not considered a risk for having a child with fragile X syndrome. [23]",
            "Document the result and individualize counseling for family context and laboratory interpretation. [23]"
          ],
          [
            "Premutation: approximately 55-200 CGG repeats",
            "Usually unmethylated; associated with risk for fragile X-associated tremor/ataxia syndrome and, in females, fragile X-associated primary ovarian insufficiency. [19]",
            "Provide genetic counseling, assess the relevant adult phenotype, and discuss transmission risk. [19][23]"
          ],
          [
            "Full mutation: more than 200 CGG repeats",
            "Usually associated with FMR1 methylation and loss of FMR1 protein expression; establishes fragile X syndrome when clinically concordant. [18][19]",
            "Initiate syndrome-specific developmental, behavioral, and medical surveillance and offer cascade family evaluation. [14][19]"
          ],
          [
            "Repeat-size or methylation mosaicism",
            "Mixed premutation/full-mutation or methylated/unmethylated cell lines can produce variable neurodevelopmental function. [19]",
            "Use the complete laboratory interpretation and clinical phenotype for counseling rather than repeat count alone. [19]"
          ]
        ]
      }
    },
    {
      "id": "test-interpretation",
      "eyebrow": "Laboratory interpretation",
      "heading": "Interpret repeat size, methylation, and mosaicism together",
      "intro": "The actionable result is the FMR1 molecular category, not a nonspecific sequencing finding.",
      "paragraphs": [
        "A definite molecular diagnosis of fragile X syndrome generally requires a full mutation exceeding 200 CGG repeats. These alleles are typically methylated, whereas premutation alleles of approximately 55-200 repeats are generally unmethylated. [19]",
        "Use an assay that can define expansion status and address methylation when a large expansion or mosaicism is possible. Repeat-primed PCR detects and localizes AGG interruptions; Southern blot detects normal alleles, larger premutations, and full mutations and determines FMR1 promoter methylation status. [19]",
        "Interpret phenotype by sex and molecular state. GeneReviews reports intellectual disability in essentially all males with a completely methylated full mutation and in about half of females with a full mutation; both repeat-size mosaicism and methylation mosaicism produce a broader functional range. [19]",
        "If targeted testing shows no CGG expansion but the patient remains clinically suspicious for a genetic neurodevelopmental disorder, proceed with broader genomic evaluation rather than relabeling the patient as having fragile X syndrome. [19]"
      ],
      "bullets": [
        "Request the laboratory report’s repeat-size category and methylation interpretation, especially for full mutations and suspected mosaicism. [19]",
        "Use AGG-interruption information, when reported, as a reproductive-counseling modifier rather than as a diagnostic substitute for repeat category. [19]",
        "Treat a premutation result as an FMR1-related disorder risk state, not as evidence that the patient has full-mutation fragile X syndrome. [19][23]"
      ],
      "subsections": [],
      "table": {
        "caption": "Testing method selection for FMR1 CGG-repeat disorders. [19]",
        "columns": [
          "Method",
          "Useful result",
          "Decision use"
        ],
        "rows": [
          [
            "Repeat-primed PCR",
            "Detects CGG-repeat expansion and identifies AGG interspersions. [19]",
            "Use for targeted FMR1 expansion detection and reproductive-risk characterization when AGG structure is relevant. [19]"
          ],
          [
            "Southern blot",
            "Detects normal, larger premutation, and full-mutation alleles and determines promoter methylation. [19]",
            "Use when methylation status or large-expansion characterization is needed. [19]"
          ],
          [
            "Multigene panel, exome, or genome testing",
            "May identify alternative etiologies but is useful for fragile X evaluation only when no CGG expansion is detected and suspicion remains. [19]",
            "Do not substitute for targeted FMR1 expansion testing. [19]"
          ]
        ]
      }
    },
    {
      "id": "post-diagnosis-care",
      "eyebrow": "Longitudinal care",
      "heading": "Organize care around developmental function and treatable comorbidities",
      "intro": "There is no established disease-modifying clinical therapy; management targets function and comorbidity.",
      "paragraphs": [
        "After DNA confirmation, arrange age-appropriate developmental and educational intervention rather than waiting for physical features to evolve. Early intervention can improve long-term cognitive outcomes, although it should not be presented as restoring normal cognitive outcome. [4][14]",
        "At follow-up, actively identify impairment from ADHD symptoms, anxiety, aggression, and sleep problems because these are recognized medication targets in fragile X syndrome. Select medication according to the dominant treatable syndrome and reassess functional benefit and adverse effects rather than treating the molecular diagnosis itself. [8]",
        "Assess for seizures when episodes suggest altered awareness, motor events, or unexplained regression. ADHD and epilepsy may coexist in fragile X syndrome; stimulant therapy and antiseizure treatment can be managed independently when both disorders are present. [11][12]",
        "Use a multidisciplinary model that links the primary clinician, developmental and behavioral services, school supports, and genetics. The AAP health-supervision guidance is specifically designed for pediatric management after DNA confirmation. [14]"
      ],
      "bullets": [
        "Document baseline communication, adaptive function, behavior, sleep, and school or work participation; use these domains to judge whether a symptom-directed intervention is helping. [8][14]",
        "Evaluate suspected seizure events with a seizure-focused history and neurologic assessment; treat confirmed epilepsy with antiseizure therapy while independently addressing clinically significant ADHD. [11][12]",
        "Review adverse effects whenever stimulants, antidepressants, or antipsychotics are used, because these agents may suppress symptoms without correcting the underlying molecular disorder and can cause side effects. [6]"
      ],
      "subsections": [
        {
          "heading": "Medication decisions",
          "paragraphs": [
            "Pharmacotherapy in fragile X syndrome is symptom-directed: reported targets include ADHD symptoms, anxiety, aggression, and sleep problems. Stimulants, antidepressants, and antipsychotics may reduce symptoms but do not address the underlying FMR1 molecular defect. [6][8]"
          ],
          "bullets": [
            "Do not represent symptomatic psychotropic treatment as disease-modifying therapy. [6][9]",
            "Match medication choice to a defined target syndrome and track target behavior, function, and adverse effects at each reassessment. [6][8]"
          ]
        }
      ],
      "table": {
        "caption": "Comorbidity-directed follow-up after confirmed fragile X syndrome. [8][11][12][14]",
        "columns": [
          "Clinical domain",
          "Assessment trigger",
          "Action"
        ],
        "rows": [
          [
            "Development and adaptive function",
            "New diagnosis or loss of expected developmental progress. [4][14]",
            "Initiate or update early-intervention, educational, and developmental supports. [4][14]"
          ],
          [
            "ADHD symptoms",
            "Function-limiting inattention, hyperactivity, or impulsivity. [8][11]",
            "Use standard ADHD-directed treatment planning; stimulant therapy can be managed independently from antiseizure treatment when epilepsy coexists. [11]"
          ],
          [
            "Anxiety, aggression, or sleep problems",
            "Symptoms cause distress, safety risk, caregiver burden, or functional deterioration. [8]",
            "Select a symptom-targeted behavioral and medication plan and monitor adverse effects. [6][8]"
          ],
          [
            "Possible seizures",
            "Paroxysmal events, altered awareness, motor episodes, or clinical concern for epilepsy. [11][12]",
            "Perform seizure-focused assessment and treat confirmed epilepsy with antiseizure therapy. [11]"
          ]
        ]
      }
    },
    {
      "id": "family-counseling",
      "eyebrow": "Cascade care",
      "heading": "Use the molecular result to counsel relatives and reproductive risk",
      "intro": "A positive FMR1 result changes care beyond the proband.",
      "paragraphs": [
        "Counsel families that fragile X syndrome results from CGG-repeat hyperexpansion in the 5′ untranslated region of FMR1, which leads to promoter hypermethylation and loss of the encoded protein in full-mutation disease. [18][21]",
        "For a woman with a premutation, explain that the allele may expand to a full mutation during maternal transmission. Repeat length and AGG interruptions influence expansion behavior; expansion from premutation to full mutation has been documented in one generation, including a 59-repeat allele lacking AGG interruptions in a pedigree analysis. [18][22]",
        "Offer targeted testing and counseling to biologically relevant relatives after identifying a full mutation or premutation. This can identify relatives at risk for fragile X syndrome, fragile X-associated tremor/ataxia syndrome, or fragile X-associated primary ovarian insufficiency and can inform reproductive planning. [15][19][23]",
        "When reproductive options are being considered, refer to reproductive genetics. Preimplantation genetic testing has used FMR1 PCR-based approaches, but large GC-rich premutation and full-mutation alleles can be difficult to amplify; linked-marker approaches may be needed to reduce misclassification risk. [18]"
      ],
      "bullets": [
        "Classify each tested relative by the largest FMR1 allele when interpreting female results, because females have two FMR1 copies and category assignment is based on the larger repeat number. [23]",
        "Do not reassure a premutation carrier solely because they do not have fragile X syndrome; counsel regarding adult FMR1-associated risks and transmission implications. [19][23]",
        "Use reproductive genetics consultation for premutation or full-mutation carriers considering pregnancy, preimplantation testing, or prenatal diagnostic options. [18][22]"
      ],
      "subsections": [],
      "table": {
        "caption": "Counseling priorities by FMR1 result. [18][19][23]",
        "columns": [
          "Result in the patient or relative",
          "Primary counseling issue",
          "Next action"
        ],
        "rows": [
          [
            "Full mutation",
            "Risk for fragile X syndrome phenotype and potential family transmission. [19]",
            "Provide syndrome management and offer cascade testing with genetics counseling. [14][19]"
          ],
          [
            "Premutation in a woman",
            "Risk of transmission of a premutation or full mutation and risk for fragile X-associated primary ovarian insufficiency. [19][23]",
            "Refer for reproductive counseling; discuss maternal expansion risk and reproductive testing options. [18][22]"
          ],
          [
            "Premutation in an adult with tremor/ataxia",
            "Possible fragile X-associated tremor/ataxia syndrome. [19]",
            "Evaluate the neurologic phenotype and coordinate neurology and genetics follow-up. [13][19]"
          ],
          [
            "Intermediate allele",
            "Does not establish fragile X syndrome or risk for having a child with fragile X syndrome. [23]",
            "Provide result-specific counseling and avoid diagnosing an FMR1 disorder on repeat count alone. [23]"
          ]
        ]
      }
    }
  ],
  "faq": [],
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  "editorialNote": "Prepared from cited clinical literature using Astra's research workflow. Verify recommendations against current guidance and patient-specific factors.",
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    {
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      "title": "Attention deficit hyperactivity disorder",
      "detail": "adc.bmj.com",
      "url": "https://adc.bmj.com/content/79/5/381",
      "authors": "adc.bmj.com",
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      "snippet": "There is also the likelihood that identifiable developmental pathology, such as fragile X or hemiplegic cerebral palsy, increases the risk for hyperactivity",
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      "host": "www.nature.com",
      "snippet": "ACMG Practice Guideline\n  Genetics in Medicine\n ### Technical Standards and Guidelines: Molecular Genetic Testing for Ultra-Rare Disorders\n\n  + Anne Maddalena\n  + Sherri Bale\n  + the ACMG Laboratory Quality Assurance Committee\n\n  ACMG Standards and Guidelines\n  Genetics in Medicine\n ### Fragile X sy",
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      "authors": "www.nature.com",
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      "snippet": "by KG Monaghan · 2013 · Cited by 185 — Clinical significance of tri-nucleotide repeats in Fragile X testing: a clarification of American College of Medical Genetics guidelines.",
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      "snippet": "Discussions are ongoing regarding the possibilities of improving the ways in which hospitals provide information to newborn screening programs to ensure that adequate information is available in a timely manner for recontacting families or health care professionals and establishing follow-up while s",
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      "snippet": "Fragile X syndrome (FXS) is a neurodevelopmental disorder caused by CGG trinucleotide repeat expansion in the fragile X messenger ribonucleoprotein 1 (FMR1)",
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      "snippet": "by AWM Hooper · 2021 · Cited by 36 — Pharmacotherapeutic treatments, such as stimulants, antidepressants, and antipsychotics, suppress the symptoms but induce side effects and do not address the",
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      "snippet": "by M Harbers · 2025 · Cited by 2 — Fragile X syndrome (FXS) is the foremost monogenic cause of autism spectrum disorder and intellectual disability, caused by FMR1 gene silencing.",
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      "authors": "onlinelibrary.wiley.com",
      "host": "onlinelibrary.wiley.com",
      "snippet": "by D Protic · 2024 · Cited by 29 — The aim of pharmacotherapy is to treat ADHD symptoms, anxiety, aggression, and sleep problems. Selective serotonin reuptake inhibitors. Anxiety",
      "score": 0.57780564
    },
    {
      "number": 9,
      "title": "Gene Therapy for Fragile X Syndrome, Challenges, and ...",
      "detail": "onlinelibrary.wiley.com",
      "url": "https://onlinelibrary.wiley.com/doi/10.1002/jgm.70049",
      "authors": "onlinelibrary.wiley.com",
      "host": "onlinelibrary.wiley.com",
      "snippet": "by M Velinov · 2025 · Cited by 3 — Strategies for therapeutic intervention for this disorder have included behavioral and medication therapy. To date, no management strategies",
      "score": 0.49831602
    },
    {
      "number": 10,
      "title": "A multidisciplinary approach to the management of ...",
      "detail": "onlinelibrary.wiley.com",
      "url": "https://onlinelibrary.wiley.com/doi/10.1111/j.1365-2788.2006.00942.x",
      "authors": "onlinelibrary.wiley.com",
      "host": "onlinelibrary.wiley.com",
      "snippet": "Background Fragile X syndrome (FXS) is the most common inherited form of intellectual disability. Since the identification of the",
      "score": 0.4892356
    },
    {
      "number": 11,
      "title": "58 Attention-Deficit Disorders and Epilepsy - Oxford Academic",
      "detail": "academic.oup.com",
      "url": "https://academic.oup.com/book/57972/chapter/476211974",
      "authors": "academic.oup.com",
      "host": "academic.oup.com",
      "snippet": "fragile X syndrome all have a high prevalence of ADHD. Both can be treated independently with antiseizure drugs and stimulant therapy, fragile",
      "score": 0.48674685
    },
    {
      "number": 12,
      "title": "Descriptive analysis of seizures and comorbidities ...",
      "detail": "onlinelibrary.wiley.com",
      "url": "https://onlinelibrary.wiley.com/doi/10.1002/mgg3.2001",
      "authors": "onlinelibrary.wiley.com",
      "host": "onlinelibrary.wiley.com",
      "snippet": "Fragile X syndrome is characterized by a myriad of physical features, behavioral features, and medical problems. Commonly found behavioral",
      "score": 0.3727797
    },
    {
      "number": 13,
      "title": "Fragile X‐associated tremor/ataxia syndrome: Clinical ...",
      "detail": "movementdisorders.onlinelibrary.wiley.com",
      "url": "https://movementdisorders.onlinelibrary.wiley.com/doi/10.1002/mds.21493",
      "authors": "movementdisorders.onlinelibrary.wiley.com",
      "host": "movementdisorders.onlinelibrary.wiley.com",
      "snippet": "The discovery of FXTAS prompted exploration of the contribution of the FMR1 premutation to disorders with similar clinical features. The results",
      "score": 0.70263255
    },
    {
      "number": 14,
      "title": "Health Supervision for Children With Fragile X Syndrome",
      "detail": "publications.aap.org",
      "url": "https://publications.aap.org/pediatrics/article/127/5/994/64903/Health-Supervision-for-Children-With-Fragile-X",
      "authors": "publications.aap.org",
      "host": "publications.aap.org",
      "snippet": "This set of guidelines was designed to assist pediatricians in caring for children with fragile X syndrome after a diagnosis has been confirmed by DNA analysis.",
      "score": 0.68874115
    },
    {
      "number": 15,
      "title": "Fragile X Syndrome (Chapter 253) | American Academy of Pediatrics Textbook of Pediatric Care | Pediatric Care Online | American Academy of Pediatrics",
      "detail": "publications.aap.org",
      "url": "https://publications.aap.org/pediatriccare/book/348/chapter/5779933/Fragile-X-Syndrome-Chapter-253",
      "authors": "publications.aap.org",
      "host": "publications.aap.org",
      "snippet": "Advanced Search\n\nSearch with book\n\nOpen figure viewer\n\nFragile X syndrome is an X-linked genetic condition characterized by trinucleotide repeats in the fragile X mental retardation 1 gene (FMR1) altering fragile X mental retardation protein (FMRP) expression.1,2 It is the most commonly inherited fo",
      "score": 0.5923135
    },
    {
      "number": 16,
      "title": "Chapter 107: The Newborn with Neurologic Findings",
      "detail": "publications.aap.org",
      "url": "https://publications.aap.org/pediatriccare/book/348/chapter/5768699/The-Newborn-with-Neurologic-Findings",
      "authors": "publications.aap.org",
      "host": "publications.aap.org",
      "snippet": "Genetic disorders such as fragile X syndrome and ... The Guidelines for Perinatal Care, coauthored by the American Academy of Pediatrics",
      "score": 0.49567938
    },
    {
      "number": 17,
      "title": "Ethical, Legal, and Social Concerns About Expanded ...",
      "detail": "publications.aap.org",
      "url": "https://publications.aap.org/pediatrics/article/121/3/e693/72799/Ethical-Legal-and-Social-Concerns-About-Expanded",
      "authors": "publications.aap.org",
      "host": "publications.aap.org",
      "snippet": "Fragile X syndrome (FXS), the most common inherited form of intellectual disability, was not recommended for screening by the ACMG, primarily because of the",
      "score": 0.46235222
    },
    {
      "number": 18,
      "title": "FMR1 CGG repeat expansion mutation detection and linked haplotype analysis for reliable and accurate preimplantation genetic diagnosis of fragile X syndrome - PMC",
      "detail": "pmc.ncbi.nlm.nih.gov",
      "url": "https://pmc.ncbi.nlm.nih.gov/articles/PMC5733830",
      "authors": "pmc.ncbi.nlm.nih.gov",
      "host": "pmc.ncbi.nlm.nih.gov",
      "snippet": "CGG-triplet repeat hyperexpansions in the 5′ untranslated region of the X-linked fragile X mental retardation 1 (FMR1) gene cause fragile X syndrome (OMIM #300624) via FMR1 promoter hypermethylation and sequential loss of the encoded FMR1 protein (Refs 1–3). Fragile X syndrome is the most common sin",
      "score": 0.78294516
    },
    {
      "number": 19,
      "title": "FMR1 Disorders - GeneReviews® - NCBI Bookshelf",
      "detail": "www.ncbi.nlm.nih.gov",
      "url": "https://www.ncbi.nlm.nih.gov/books/NBK1384",
      "authors": "www.ncbi.nlm.nih.gov",
      "host": "www.ncbi.nlm.nih.gov",
      "snippet": "| Variant Type | # of CGG Trinucleotide Repeats | Methylation Status of FMR1 | Clinical Status | |\n ---  --- \n| Male | Female |\n| Premutation | ~55-200 | Unmethylated | At risk for FXTAS 1 |  At risk for FXPOI & FXTAS  Potential ↑ risk of other fragile X-assoc disorders 1 |\n| Full mutation | >200 | ",
      "score": 0.7621591
    },
    {
      "number": 20,
      "title": "Development of Genetic Testing for Fragile X Syndrome and ...",
      "detail": "pmc.ncbi.nlm.nih.gov",
      "url": "https://pmc.ncbi.nlm.nih.gov/articles/PMC5192486",
      "authors": "pmc.ncbi.nlm.nih.gov",
      "host": "pmc.ncbi.nlm.nih.gov",
      "snippet": "by JN Macpherson · 2016 · Cited by 32 — The progressive expansion of a CGG repeat in the FMR1 gene from “premutation” to “full mutation” provided an explanation for the “Sherman",
      "score": 0.71185225
    },
    {
      "number": 21,
      "title": "FMR1 premutation and full mutation molecular mechanisms ...",
      "detail": "pmc.ncbi.nlm.nih.gov",
      "url": "https://pmc.ncbi.nlm.nih.gov/articles/PMC3261276",
      "authors": "pmc.ncbi.nlm.nih.gov",
      "host": "pmc.ncbi.nlm.nih.gov",
      "snippet": "by R Hagerman · 2011 · Cited by 122 — Fragile X syndrome (FXS) is caused by an expanded CGG repeat (>200 repeats) in the 5′ un-translated portion of the fragile X mental retardation 1 gene (FMR1)",
      "score": 0.7038554
    },
    {
      "number": 22,
      "title": "Expansion of the Fragile X CGG Repeat in Females with Premutation or Intermediate Alleles - PMC",
      "detail": "pmc.ncbi.nlm.nih.gov",
      "url": "https://pmc.ncbi.nlm.nih.gov/articles/PMC379237",
      "authors": "pmc.ncbi.nlm.nih.gov",
      "host": "pmc.ncbi.nlm.nih.gov",
      "snippet": "In figure 2 and table 4, we have summarized the FMR1 CGG repeats in 136 offspring of 92 mothers with intermediate alleles with 49–65 repeats and with no family history of fragile X. The intermediate alleles were limited to the larger sizes, since there is virtually no risk of expansion to a full mut",
      "score": 0.6929958
    },
    {
      "number": 23,
      "title": "How Fragile X Syndrome Is Inherited | Fragile X Syndrome (FXS) | CDC",
      "detail": "www.cdc.gov",
      "url": "https://www.cdc.gov/fragile-x-syndrome/about/how-fragile-x-syndrome-is-inherited.html",
      "authors": "www.cdc.gov",
      "host": "www.cdc.gov",
      "snippet": "### Normal: 5 to 44 Repeats\n\nMost males have about 5 to 44 repeats of the chemical letters, CGG, in their FMR1 gene and most females also have 5 to 44 repeats in each of their FMR1 genes. This is considered a normal number of repeats. People with a normal number of repeats do not have FXS and do not",
      "score": 0.6628188
    },
    {
      "number": 24,
      "title": "A methylation PCR approach for detection of fragile X ...",
      "detail": "pubmed.ncbi.nlm.nih.gov",
      "url": "https://pubmed.ncbi.nlm.nih.gov/10447261",
      "authors": "pubmed.ncbi.nlm.nih.gov",
      "host": "pubmed.ncbi.nlm.nih.gov",
      "snippet": "by I Panagopoulos · 1999 · Cited by 54 — Fragile X syndrome is associated with the expansion of the number of CGG trinucleotide tandem repeats at the 5' untranslated region of the FMR1 gene.",
      "score": 0.6485337
    }
  ],
  "publishedAt": "2026-08-24T18:02:01.848629+00:00",
  "updatedAt": "2026-08-24T18:02:01.848629+00:00",
  "readingMinutes": 5,
  "slug": "fragile-x-syndrome"
}