18q deletion syndrome

• Disease description (causes and symptoms)

  • Definition and causes: 18q deletion syndrome (18q monosomy) is a chromosomal disorder caused by deletion of part of the long arm of chromosome 18 (long arm: q arm). Most cases occur spontaneously (de novo mutations), but in rare cases they may be inherited due to structural chromosomal abnormalities in a parent (such as a translocation). The location and size of the deletion vary (for example, between 18q21 and 18q23), and larger deletions tend to cause more severe symptoms.
  • Brief pathophysiology: Deletion of specific genes on the long arm can affect neurodevelopment, muscle tone, growth, the sensory organs, and genitourinary development, resulting in a variety of clinical features.
  • Main symptoms (representative phenotype)
    • Developmental delay and intellectual disability (mild to moderate; a wide IQ range, possibly approximately 40–85 according to reports)
    • Hypotonia (low muscle tone) and motor incoordination, as well as movement disorders such as chorea and athetosis
    • Microcephaly or craniofacial abnormalities: midface hypoplasia, deep-set eyes, a short nose, a thin and short upper lip, changes in the shape of the mouth, malformed external ears, external auditory canal atresia, and others
    • Sensory impairment: hearing loss (due to external ear malformations or middle-ear problems), with possible visual abnormalities
    • Growth delay, low weight, and short stature
    • Genital abnormalities (such as undescended testes and hypospadias in boys)
    • Skeletal abnormalities (long, slender fingers; foot deformities, etc.), and spinal or joint problems
    • Other: seizures (rare), endocrine abnormalities (such as growth or thyroid abnormalities), or accompanying cardiac or gastrointestinal malformations

• Treatment methods

  • General principles: Since there is no treatment that corrects the underlying genetic deletion, multidisciplinary, symptom-specific management is used to maximize function and prevent complications.
  • Medication: Standard drug treatment is provided for specific symptoms (such as seizures and hypothyroidism). Medications to improve muscle tone may be considered selectively depending on the symptoms and age.
  • Surgery/procedures: Appropriate surgical correction is performed for external auditory canal atresia and middle-ear malformations (hearing loss), hypospadias and undescended testes (urological correction), and cardiac or gastrointestinal malformations.
  • Rehabilitation and education: Physical therapy (to promote motor development), occupational therapy, speech therapy (assessment and treatment of speech and swallowing disorders), and special education and developmental therapy are essential.
  • Screening and follow-up: Multidisciplinary monitoring, including hearing and vision tests, monitoring of growth and endocrine function (such as the thyroid), regular neurodevelopmental assessments, and orthopedic, dental, and otolaryngology evaluations.
  • Genetic counseling: Assessment of the recurrence risk for the parents and family (parental chromosome testing is recommended), counseling when planning a pregnancy, and guidance on prenatal diagnosis when necessary.
  • Lifestyle management and precautions: Adjust eating methods in cases of aspiration or swallowing difficulty; ensure vaccination and infection control; prevent falls and injuries; and continue participation in treatment and rehabilitation.

• Outpatient visit checklist (including example questions)

  • Items and documents to prepare
    • List of current medications and supplements (including dosage and duration)
    • Results of previous surgeries, hospitalizations, and tests (such as hearing, vision, genetic, and chromosome tests), preferably copies
    • Growth records (height and weight), and developmental history (when the child began rolling over, sitting, walking, and speaking)
    • Family history (similar symptoms and whether the parents have undergone chromosome testing)
    • Records of recent symptom changes and photographs of concerning findings (such as the face, ears, or limbs), and notes on hearing or vision abnormalities
  • Things to do before the visit
    • Confirm medication use (continue taking current medications as usual)
    • If there have been changes in symptoms (such as seizures, swallowing difficulty, or decreased hearing), record the dates and circumstances
  • Items the medical staff may ask about during the outpatient visit (examples)
    • “When did the developmental delay begin?”
    • “Have there been any recent seizures or losses of consciousness?”
    • “Have there been any changes in hearing or language development?”

• Examples of general questions to ask the doctor

  • “How was the diagnosis of this condition (the location and extent of the deletion) confirmed? Are additional tests needed?”
  • “What treatments (surgery, rehabilitation, or medication) are recommended for the current symptoms, and what is the priority?”
  • “How can the prognosis be predicted, and how should we prepare for daily life and educational support?”

• Examples of condition-specific questions

  • “What are the exact location (for example, where between 18q21 and 18q23) and size of my (or my child’s) 18q deletion? How might the genes included in the deletion affect the prognosis?”
  • “What is the recurrence risk when planning a future pregnancy, and should parental chromosome testing or prenatal testing (chorionic villus sampling, amniocentesis, exome sequencing/microarray, etc.) be performed?”

(Note: Standard cytogenetic testing (standard chromosome testing) and higher-sensitivity array testing (chromosomal microarray, array CGH) are used for diagnosis. Treatment and follow-up should be individualized according to the patient’s condition and accompanying malformations.)