Practice question

Edward syndrome corresponds trisomy 18 karyotype 47,XX+18 or 47,XY+18 arising maternal nondisjunction often meiosis II error. Clinical presentation includes severe intellectual disability, failure thrive low birth weight, prominent occiput, low set ears, clenched fists overlapping fingers characteristic, rocker-bottom feet, cardiac septal defects leading high mortality first year around 90 percent. Larger chromosome than 21 carries more developmental genes dosage imbalance more severe than Down syndrome, incidence rarer due higher prenatal loss and spontaneous abortion. Median survival weeks to months, few survive years requiring intensive care.