Q91.0

Clinical Causes: Trisomy 18 results from a random error during cell division in the formation of reproductive cells (eggs or sperm). Specifically, meiotic nondisjunction is the primary cause, leading to an ovum or sperm cell with an extra copy of chromosome 18. When this cell contributes to conception, the resulting embryo has three copies of chromosome 18 instead of the usual two, a condition known as trisomy. This event is generally not inherited but occurs sporadically. Factors that may influence the risk include maternal age, with older mothers having a higher likelihood of conceiving a child with trisomy 18. However, most cases happen randomly and are not linked to family history.

Key Symptoms: Infants born with trisomy 18 often display a complex array of physical and developmental features, including: - Low birth weight and slow growth - Abnormal head shape, such as a small head (microcephaly) - Abnormally shaped ears - Low-set ears - Very small jaw (micrognathia) - Clenched fists with overlapping fingers - Rocker-bottom feet - Heart defects - Breathing difficulties and other respiratory problems - Low muscle tone (hypotonia) - Severe intellectual disabilities - Abnormalities of the kidneys or other internal organs - Feeding difficulties and failure to thrive The severity of symptoms can vary, but many affected individuals face significant challenges, with a large proportion not surviving beyond the first year of life.

Diagnosis Path: Diagnosis of trisomy 18 is typically made through genetic testing. Methods include: - Prenatal screening tests such as ultrasound assessments that might detect characteristic physical features - Diagnostic procedures like chorionic villus sampling (CVS) or amniocentesis, which analyze fetal chromosomes - Postnatal genetic testing on blood samples to confirm the presence of an extra chromosome 18 These tests help confirm the diagnosis and guide medical decision-making and parental counseling.

Treatment Protocols: There is no cure for trisomy 18, and treatment mainly focuses on supportive care aimed at managing symptoms and improving quality of life. Approaches include: - Surgery to correct heart defects and other treatable abnormalities - Respiratory support for breathing issues - Nutritional support, including feeding assistance or tube feeding - Physical, occupational, and speech therapies to support development - Regular monitoring and management of associated health conditions Decisions about the level of medical intervention are typically made based on the severity of the condition, the individual’s overall health, and family preferences. Given the complex medical needs, care from a multidisciplinary team is often considered essential.