Fragile X is a condition caused by abnormally long extension of a triplet nucleotide repeat on the X chromosome. Mostly males are affected as they don't have an additional X chromosome to make up for the defect.
Fragile X hereditary and might be passed by healthy females to their sons. Trouble is, most of the times the carrier female does not know that she's a carreir until she's had a sick boy. On genetic testing, her own triplet repeat might be slightly extended in length or within normal range. The reason for her having children with the fragile X is that the nucleotide triplet expands between generations (sorry, if I have to explain it properly I will have to use a lot of additional terminology). Usually, once a woman has had one sick son she is considered a carrier (though it might not be the case but if further details are needed, I am ready to elaborate on this).
Usually, the risk of a female carrier having a child with fragile X is about 25 % for all children and 50 % for the boys. It must be considered, however, that while girls don't usually have manifest disease, they might have inherited a defective X chromosome which, in turn, might result in them having sons with Fragile X.
I provide brief synopsis of the clinical features that are characteristic of the Fragile X syndrome in boys:
Affected male individuals may have long face, high forehead, large mouth with long upper middle incisors, thick lips, high-arched palate, large jaw with prominent chin, and large ears. A lot of the affected males have macroorchidism (enlarged testes).
Mental retardation could be very variable, but language development is usually very delayed. Motor development is often delayed.
Source: Online Mendelian Inheritance In Men (OMIM).
The late language and motor development is sometimes mistaken for signs of autism in young boys, as the characteristic face features usually become more prominent later in life and the macroorchidism would not show until puberty. Fragile X, however, can be diagnosed definitively by chromosome tests and it is not considered to be related to autism. That is, the affected individuals might exhibit some characteristics which are common in autism, but that does not mean that they are autistic. (For an example, autistic people might look and act as mentally ret*d people (and by Jove, I am sure that everybody on the spectrum has at least once been caled 'ret*d' but mental retardation is not an obligatory feature in autism, on the contrary, autists and Aspies often have normal to superior intelligence).
There are prenatal tests for detection of a male fetus affected by fragile X early in pregnancy and they are done practically in all genetic centers or genetics departments of large ob/gyn clinics. While there aren't tests for autism yet, even though we know that it is highly hereditary.
Anyway, official medicine does not recognise Fragile X to be part of the autistic spectrum disorders. Neither is Down syndrome, as a matter of fact. You only have a limited set of neurological disfunction that are not that severe so as to allow the affected individual to live beyond intrauterine life and early infancy. It's not that strange then that we might have symptoms that are common between several different disorders.
07 Oct 2010, 8:24 pm
My first son had the test and he didn't have it. I wonder if my second son would have it or not, I know for certain he inherited the other X. He does have soft skin and flexible joints, but nothing else.
