Genetic disorders

Question 1

Why study genetic disorders?

Answer 1

• Clinical practice - identify disorders, HGP.

- Theory - unique opportunity to see what genes do. Pinker (2001) ‘dawn of cognitive genetics’.

Question 2

What is the prevalence of phenylketonuria, what is it, and what gene is it caused by?

Answer 2

• 1 in 10,000

Question 3

Define autosomal.

Answer 3

Genetic but not linked to sex chromosomes.

Question 4

What is the prevalence of Huntington’s Disease, what is it, and what gene is it caused by?

Answer 4

• 1 in 10-20,000

Question 5

What is phenylketonuria?

Answer 5

Metabolic disorder which untreated can result in mental retardation and seizures - used to be responsible for 1% of hospitalised cases of learning disability.

Question 6

What is the cause of phenylketonuria?

Answer 6

• Malfunction in the pathway producing the amino acid tyrosine.
• Autosomal recessive disorder on chromosome 12

Question 7

What is Huntington’s Disease?

Answer 7

Characterised by involuntary movements, personality changes and forgetfulness becoming noticeable around the age of 40.

Question 8

What is the cause of Huntington’s Disease?

Answer 8

• Due to progressive damage of the basal ganglia and cortex

- Autosomal dominant, chromosome 4.

Question 9

What are sporadic mutations?

Answer 9

Mutations that occur in the individual - they aren’t inherited from parents. They are usually due to errors in segregation when gametes are produced.

Question 10

What are examples of sporadic mutation genetic disorders?

Answer 10

Down’s syndrome and William’s syndrome.

Question 11

What is Down’s syndrome?

Answer 11

• Symptoms include facial dysmorphology, short stature and learning difficulties.
• IQ usually around 55, but performance and cognitive profile vary.

Question 12

What is the prevalence of Down’s syndrome?

Answer 12

• 1 in 1,000 but increases with age of parents

Question 13

What is the cause of Down’s syndrome?

Answer 13

• Abnormality in chromosome numbers

- Majority due to trisomy of chromosome 21.

Question 14

What is William’s syndrome?

Answer 14

• Symptoms include low IQ (50-70) and some facial dysmorphology.
• Also an uneven profile of cognitive abilities (of great interest): dissociation between language and general cognitive abilities.

Question 15

What is the prevalence of William’s syndrome?

Answer 15

Approx. 1 in 2,000.

Question 16

What is the cause of William’s syndrome?

Answer 16

• Microdeletion on chromosome 7

Question 17

Why are X-linked disorders easier to detect?

Answer 17

Because they’re inherited differently for males and females.

Question 18

What was the first reported case of X-linkage?

Answer 18

Colour blindness

Question 19

What disorders are caused by changes in the number of X chromosomes?

Answer 19

Turner’s syndrome and Klinefelter syndrome.

Question 20

What is the cause and prevalence of Turner’s syndrome?

Answer 20

• X0

- 1 in 2,500 births (women only).

Question 21

What are the symptoms of Turner’s syndrome?

Answer 21

• Short stature
• Infertility
• Verbal IQ normal, performance IQ can be a bit lower.

Question 22

What is the cause and prevalence of Klinefelter syndrome?

Answer 22

• X(+)XY

- 1 in 750 births (men only)

Question 23

What are the symptoms of Klinefelter syndrome?

Answer 23

• Hormone imbalances (treatable)
• Below average IQ.
• Speech and language difficulties.
• Breast development, poor beard growth, long legs and wide hips.

Question 24

What is Fragile X syndrome caused by?

Answer 24

A single gene dysfunction on the X chromosome.

Question 25

What is the prevalence of Fragile X syndrome?

Answer 25

1 in 2-4,000 for males, 1 in 6,000 females.

Question 26

What are the symptoms of Fragile X syndrome?

Answer 26

Complex profile of relative cognitive strengths:

• Repetitive language
• Difficulties with visuo-spatial cognition and attention.