DS

Question 1

DS-genotype

Answer 1

• Trisomy 21 (47, XX or XY, +21) due to nondisjunction in meiosis (usually maternal, incidence goes up with maternal age)
• mosaicism
• parent is a balanced carrier (Robertsonian translocation) and passes this on, so person with DS has unbalanced translocation of 21 and another acrocentric chromosome (ex. 14…46, XY, t(14q21q)

Question 2

DS-phenotype

Answer 2

• newborns: “floppy,” hypotonia
• webbed neck
• ID
• distinctive facial features (flat nasal bridge, small mouth, large tongue, small eyes)
• short stature
• brushfield spots
• ear infections due to malformation of ear
• excessive joint flexibility
• high incidence of AVSDs/VSDs
• extra space between big toe and first little toe

Question 3

DS-diagnosis and screening

Answer 3

fetal screening: quad test, ultrasound, amnio, CVS

diagnosis: karyotype