Compare and contrast two or three intellectual development disorders discussed in the text in terms of behavioral phenotypes and specific genotypes

What will be an ideal response?

• Down syndrome
o Genotype: extra 21st chromosome (also known as trisomy 21)
o Behavioral phenotypes: distinct facial features, heart problems, poor muscle tone; mild to severe cognitive and language delays; strengths include visual short-term memory, usually happy and easy-going ("Prince Charming"), few maladaptive behaviors; some externalizing and internalizing symptoms
• Williams syndrome
o Genotype: microdeletion on chromosome 7
o Behavioral phenotypes: deficits in cognitive functioning and spatial skills; strengths in language and music domains; strengths in empathy and reading facial and emotions in others; quite social which may lead to concerns about boundaries and possibility of victimization; numerous fears and anxieties
• Fragile X syndrome
o Genotype: mutation on the FMRI gene; more common in boys
o Behavioral phenotypes: fewer physical characteristics but can have large head circumferences, loose joints, and unusual facial features; several behavior difficulties including anxiety, poor attention, and low adaptability; difficulties relating to others; autistic-like behaviors