This book describes Fragile X Syndrome, Diagnosis and Treatment and Related Diseases
Fragile X syndrome (FXS) is a genetic disorder, the second most frequent cause of genetically linked mental deficiencies, after trisomy 21.
A genetic disorder indicates that there are alterations to the person's genes.
Fragile X syndrome (also termed Martin-Bell syndrome or Marker X syndrome) is the most frequent cause of inherited mental retardation, intellectual disability and autism.
The conservative estimates are that fragile X syndrome involves about 1 in 2500-4000 males and 1 in 7000-8000 females.
The incidence of female carrier status has been evaluated to be as high as 1 in 130-250 population.
The incidence of male carrier status is evaluated to be 1 in 250-800 population
FXS is caused by alterations in the fragile X mental retardation 1 (FMR1) gene.
The FMR1 gene normally makes a protein termed fragile X mental retardation protein (FMRP).
FMRP is required for normal brain development.
People who have FXS do not produce this protein.
People who have other fragile X-linked disorders have alterations in their FMR1 gene but normally produce some of the protein.
FXS involves both males and females.
The females often have milder symptoms than males.
The precise number of people who have FXS is not known but it has been evaluated that about 1.4 per 10,000 males and 0.9 per 10,000 females have FXS.
The gene for Fragile X is present on the X chromosome.
Since both males (XY) and females (XX) have at least one X chromosome, both can transmit the mutated gene to their children.
A father with the altered gene for Fragile X on his X chromosome will transmit that gene on only to his daughters.
To his sons he will pass on a Y chromosome, which does not transmit Fragile X syndrome.
A father with the altered gene on his X chromosome and a mother with normal X chromosomes can have daughters with the altered gene for FXS while their sons would not have the mutated gene.
A father can transmit the pre-mutation form of the FMR1 gene to his daughters but not the full mutation.
Even if the father himself has a full mutation of this gene, it seems that sperm can transmit only the pre-mutation.
Mothers transmit only X chromosomes to their children, so if a mother has the altered gene for Fragile X, she can transmit that gene to either her sons or her daughters.
If a mother has the mutated gene on one X chromosome and has one normal X chromosome, and the father has no mutations, all the children have a 50-50 possibility of inheriting the mutated gene.
These 50-50 possibility apply for each child the parents have.
Having one child with the FMR1 mutation does not raise or reduce the possibilities of having another child with the mutated FMR1 gene.
This also applies to the severity of the symptoms.
Having one child with mild symptoms does not indicate that the other children will have severe symptoms, and having a child with severe symptoms does not indicate that the other children will have mild symptoms.
Symptoms
Signs that a child might have FXS are:
1. Developmental delays (not sitting, walking, or talking at the same time as other children the same age);
2. Learning disabilities (trouble learning new skills); and
3. Social and behavior disorders
Patients with fragile X syndrome manifest with problems in these:
1. Developmental
2. Cognitive
3. Neuropsychological
4. Musculoskeletal
5. Feeding
6. Toilet training
7. Sleep
8. Recurrent medical disorders
Fragile X syndrome can be diagnosed by testing a...