1.2.2 Describe the aetiology of Fragile X Syndrome

Question 1

What happened to the X Chromosome in fragile X syndrom?

Answer 1

The FMR1 gene on the X chromosome mutated, and lengthened one arm. When the gene lengthens it switches off a protein that is important for brain development and other functions.

Normally the FMR1 gene ‘repeats’ itself 6-50 times, but in Fragile X premutation repeats between 50 and 200 times… If you have this premutation, you are a carrier of Fragile X. When the gene repeats more than 200 times, you suffer from Fragile X.

Question 2

Explain the male/female relationship of Fragile X.

Answer 2

Daughters born to male carriers inherit their X gene, and so they will be carriers too.

Sons born to male carriers don’t inherit the X gene, so fathers can’t pass it to sons.

Because women have two X chromosomes, children of either gender born to female carriers will have 50% chance of inheriting the gene.

If they inherit the gene, they will either be carriers of have the full mutation Fragile X.

Question 3

What do fragile X people physically present as?

Answer 3

long narrow face
prominent ears
big balls
big heart
high palate
heart murmur
low muscle tone and loose joints

Question 4

How do fragile X people cognitively present?

Answer 4

cognitive difficulties (mild-moderate ID)
good language development
attention deficit and hyperactivity; memory, visuo-spatial, motor and executive function difficulties

Question 5

What is the prevalence in males/females?

Answer 5

1: 1000 males
1: 2000 females

Question 6

How common is Fragile X?

Answer 6

Second most common ID (first is Downs Syndrome)