Sex chromosome disorders

Question 1

Fragile X incidence

Answer 1

-1/3000

Question 2

Fragile X

Answer 2

• most common inherited cause of LD
• most individuals have an IQ of less than 50
• accounts for 10-12% of LD in men
• nearly 50% meet criteria for autism

Question 3

Genetics Fragile X

Answer 3

CGG tripleat repeat on the dista l part of the long arm of the X chromosome (Xq27.3-FMR1)
-FMR1 gene is needed for normal neuronal development

Question 4

Clinical features of fragile X

Answer 4

• large head
• large ears
• long narrow face
• short
• macro-orchidism
• hyperextensible joints
• epilepsy in 20-25%
• mild LD in women
• moderate LD in men

Question 5

Behaviour features of fragile X

Answer 5

• hyperactivity
• inattention
• anxiety
• stereotypies
• SLT delays
• IQ decline
• mannerisms
• shyness
• gaze avoidance
• poor peer relationships
• communication difficulties

Question 6

Brain imaging in fragile X

Answer 6

• enlarged ventricles, hippocampus and caudate nuclei

- Reduced posterior cerebellar vermis

Question 7

CGG repeats

Answer 7

• the higher the number of repeats the lower the IQ
• lower IQ in males with fragile X
• most pronounced between the ages of 8-12 and stabilises by puberty

Question 8

Turners syndrome

Answer 8

• 45X
• occurs in 1/2000-1/5000 females
• 99% Turner’s are thought to end in stillbirth or spontaneous abortion

Question 9

Clinical features of turners

Answer 9

• short stature
• low hairline
• low set ears
• broad chest
• widely spaced niples
• webbed neck
• obesity
• ovarian failure occurs before birth and puberty doesnt occur naturally
• does not cause LD

Question 10

Heart defects in Turners

Answer 10

-12% have VSD or coarctation of the aorta

Question 11

Triple X syndrome

Answer 11

• trisomy X, or XXX
• extra X chromosome in each cell of a human female
• occurs in 1:1000 female births
• 60-70% have mild LD
• delayed language development, poor motor control, accelerated growth until puberty, premature ovarian failure
• associated with anxiety and increased incidence of schizophrenia

Question 12

Klinefelters syndrome

Answer 12

• 47, XXY
• common :1:500- 1:1000
• primary feature is sterility
• sparse body hair, hypogonadism, gynaecomastia
• taller than average, thin
• median IQ 90

Question 13

XYY male

Answer 13

• human male has extra copy of Y chromosome (47 XYY)
• occurs 1:1000
• often associated with behavioural problems
• IQ may be slightly lower than average
• may be more common with crime