Learning disability Flashcards
IQ of mild LD:
50-69
IQ of moderate LD:
35-49
IQ of severe LD:
20-34
IQ of profound LD:
<20
What are the different causes of Down’s syndrome?
Trisomy 21
Translocation
Mosaicism
What is trisomy 21?
Accounts for 95% cases of Down’s syndrome. There are 3 copies of Chr 21 due to non-disjunction (uneven division during meiosis)
What is translocation?
Accounts for 4% of cases of Down’s syndrome. Part of Chr 21 is attached to another Chr, usually 14 or 22
What is mosaicism?
Accounts for 1% of cases of Down’s syndrome. Some cells have 2 copies of Chr 21, others have 3
What causes Fragile X syndrome?
Area on an X chromosome of excessive trinucleotide repeats in the DNA. Clinically apparent at >200 repeats
How does Fragile X syndrome present?
Large head + ears; long face and nose; large testicles; variable LD; epilepsy; connective tissue disorder - e.g. mitral valve prolapse/lax joints; language and behavioural problems
What is the cause of PKU?
An autosomal recessive condition due to a mutation of the phenylalanine hydroxylase gene on chromosome 12
What is the result of PKU?
Mutation = unable to convert phenylalanine to tyrosine
= accumulation of phenylalanine
What is the screening test for PKU?
The Guthrie test
What is the cause of Prada-Willi syndrome?
Part of the paternal chromosome 15 is missing due to either a deletion (70%), maternal disomy – 2 copies from mother (~30%), or a mutation (v. rare)
How does Prada-Willi syndrome present?
- Short stature
- Hyperphagia, and thus marked obesity
- Failure to thrive
- Hypotonia
- Congenital dislocation of hips
- Rectal prolapse and bowel obstruction
- Hypogonadism in adults, with few secondary sexual characteristics
- Mood swings/aggression
- Self-injuring behaviour - e.g. skin picking
- OCD behaviour
