Facio Scapulo Humeral MD Explained
Can FSHD be diagnosed from a blood sample?
he DNA mutation causing FSHD can indeed be recognised from a blood sample in most people with this condition. However, interpretation of the test is not always easy, and the DNA sample will need to be forwarded to one of a few molecular genetic laboratories able to offer this. In individual cases it can be harder to exclude the diagnosis than to confirm it, although both are usually made easier if blood samples are also taken from both parents of a possible affected person.
In families where there are several people known to be affected, confirmation of diagnosis, or genetic prediction for an individual family member, will almost always be possible if blood samples are collected from several of the affected people.
Is there always a family history?
person diagnosed with FSHD, particularly if this is in early childhood, may have a fresh mutation (ie. they have not inherited it from either of their parents). More often, however, a person diagnosed with FSHD will have inherited the faulty gene from one of his or her parents. It may be that a newly diagnosed person finds that there is a family history, but that this had not been recognised before because the symptoms of other family members had been very mild, or had been misdiagnosed. We now also know that in a significant proportion of even quite early onset cases in children, who appear to be the first ones in a family, one of the parents can show the same FSHD mutation in some of their cells but not in others. This ‘mosaic' situation in the parent may not give any symptoms in them, but does mean that further children of theirs would have a risk of being affected. We would therefore always recommend that both parents be invited to provide blood samples for DNA study if they wish to know about potential risk to future children.
In other cases genetic testing may help resolve any uncertainty over the affected status of a young adult. Family members or couples seeking further information should refer to their local Clinical Genetics Service.
How severely affected would my sons and daughters be?
he age at onset of symptoms, and hence the severity of FSHD, seems to correlate broadly with the extent of the DNA rearrangement on chromosome 4, which, once it has arisen, remains a fixed size in a family. Thus there will be some families where FSHD will always tend to be quite severe, and others where it will always be relatively mild. However, there can still be considerable variation within a family for severity and age at onset. Partly, this is due to differences between men and women. Although men and women develop the same symptoms, males tend to develop these earlier, and be more severe at a given age than females. By age 30 years, just about all males with FSHD exhibit symptoms, but only two-thirds of females do.
We now know that some people (particularly men) with average or mild presentations of FSHD, may, if they are the first cases in a family, have a mixture of normal and FSHD-type cells and their offspring, who have inherited the FSHD mutation, would do so in all their cells, and therefore present earlier and more severely.
Data from many families suggests that offspring inheriting the faulty gene are likely to be affected from a similar young age and at least as severely as occurred in their affected parent, although in large families affected daughters with FSH might be milder than their fathers.
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