From this scheme it can be seen that carriers are those with 50- 200 repeats, and sufferers are those with greater than 200 repeats. The embryo should have equal proportions of each chromosome, however the chromsome with the mutant FMR1 gene is more likely to be in the child than the normal chromosome. It is thought that the mutant FMR1 gene offers some developmental advantage over the normal FMR1. Symptoms Mental retardation from moderate to profound. Some patients have behavioural abnormalities, such as autism, hyperactivity, and poor social contact.
Females usually have less severe symptoms.
The fragile X syndrome.