Diagnostics Lec 9

Question 1

What is fragile X syndrome

Answer 1

most common inherited learning disability it causes a range of development problems

Question 2

What is the cause of Fragile X syndrome

Answer 2

Mutation of fragile X mental retardation (FMR1) gene on chromosome Xq27.3

Question 3

What happens as a results of the X mutation

Answer 3

Expansion of CFF triplet repeat
- normally 5-40 times
- turn off the FMPR protein production which plays a role in the development of synapses

Question 4

What inheritance pattern does Fragile X syndrome follow

Answer 4

Atypical Mendelian Inheritance

Question 5

What does the FMR1 gene encode for

Answer 5

the FMRP

Question 6

What is FMRP a regulator of

Answer 6

neuronal protein translation = learning and memory

Question 7

What are the three states of mutation causing Fragile X syndrome

Answer 7

Normal
Premutation
Mutation

Question 8

Outline patient features during the premutation state

Answer 8

IQ in normal range but possible long term effects

Males progressive fragile X tremor/ataxia syndrome (FXTAS)

Females premature menopause

Question 9

Outline features of a male patient during the mutation state

Answer 9

Significant learning disabaility

Question 10

Outline features of a female during the mutation state

Answer 10

normal/mild/moderate learning disability

Question 11

List some other genetic disorders caused by repeat expansion

Answer 11

Several well known pathogenic conditions

Gene mutation causing disease known

Underlying genetic defect causing repeat expansion unknown

Question 12

What is Triplet repeat-primed PCT (TP-PCR)

Answer 12

PCR method to diagnose repeat expansion disease

Question 13

How does TP-PCR work

Answer 13

One primer hybridises to unique sequence
This primer has fluorescent label for detection by capillary gel electrophoresis
One primer hybridises to junction of unique sequence and repeat sequence
This primer can also hybridise anywhere within the repeat sequence

Question 14

What is observed in TP-PCR

Answer 14

multiple PCR fragments
- full length
- intermediate lengths varying by 3 nucleotides

Question 15

In a heterozygous female how is DNA for testing isolated

Answer 15

from blood sample

Question 16

In a heterozygous female, what are TP-PCR results analysed for

Answer 16

FMR1 gene

Question 17

What results can be seen upon analysis of FMR1 gene in a heterozygous female

Answer 17

two alleles with repeat copy number in normal range

23 and 33 repeats

Question 18

What results can be seen upon analysis of FMR1 gene in pre-mutation state male

Answer 18

Multiple peaks observed with periodicity of 3 nucleotides with a single major peak
Male, one X-chromosome therefore one FMR1 allele
Average peak size indicates 72 repeats
Between 55 and 200, therefore pre-mutation unaffected but might be long term implications

Question 19

What results can be seen upon TP-PCR analysis of FMR1 gene in the full mutation state male

Answer 19

Multiple peaks observed with periodicity of 3 nucleotides with a single major peak
Male, one X-chromosome therefore one FMR1 allele
Average peak size indicates 237 repeats
>200, therefore mutation and will have significant learning difficulties