case 3

[md90]

A 6-year-old boy is followed by his pediatrician for delayed language acquisition and behavioral problems at school. His mother reports a normal pregnancy with adequate prenatal care and adds that she did not use drugs or alcohol during the pregnancy. Genetic analysis reveals a normal 46,XY karyotype but an abnormal-appearing X chromosome. PCR analysis reveals an abnormal region on the X chromosome with 200 CGG trinucleotide repeats.

1. What is the most likely diagnosis?
2. What is PCR?
3. What is the inheritance pattern of this condition?
4. What are the other trinucleotide repeat disorders, and why are they associated with "premutation"?
5. What are the major preventable causes of mental retardation?

[IMG SURVIVOR]

1=Dx fragil x syndrome
3=related to the X
4- hungtinton,hemophilia,duchen muscular dystrophy

Im right? or way off

[md90]

1=Dx fragil x syndrome
3=related to the X
4- hungtinton,hemophilia,duchen muscular dystrophy

Im right? or way off

Good job, IMG!!! 2.5/3 are right except that duchenne is not a repeat disorder...; it's not muscular dystrophy BUT myotonic dystrophy

What I would add:
3. X-linked disorder... look below for a follow-up question...
4. other diseases include: fredrich's ataxia, some forms of spinocerebellar ataxia; and why "premutations"... patients with an intermediate number of repeats are said to have the premutation.. and are clinically normal BUT is their children who are at risk.. increasing the number of repeats and expressing the disease;

for the unanswered questions;
2. PCR: used to amplify copies of genes to help with detection
5. preventable causes include: maternal drug or alcohol use and nutritional deficiencies..

follow-up questions:
1. Define what is a X-linked disorder.
2. What gene is silenced in Fragile X syndrome?