A question about genetics.

[MegaLegs]

Thought I'd post in health rather than SN as I know there are many clever, sciencey mnetters about.

My 2 year old has Developmenatl Delay which so far has no dx. The report from his latest assessment at the Child development centre arrived today and I wanted to check something.

He has had bloods taken for genetic testing. The tests haven't all been done yet but they have found he is neg for Fragile x and the bit I wanted to ask about, his caryo type (although I think it should be karyo)is normal. From what I understand that means he has a normal set of matching chromosomes - is that correct?

yep, spot on (and you're right, it's karyotype)

The first genetic tests done are often Fragile X and Karyotype.

This (Karyotype) is a VERY basic chromasome test and will often show nothing amiss unless there is a major deletion, translocation or duplication.

MegaLegs, as you say, it means that your ds has no major chromosome changes (none missing or duplicated). I have been trying to think of an analogy- if you imagine an image of the UK taken from space, then that is the karyotype, and your ds's looks normal. However, even if Manchester was missing, you wouldn't notice on a map at that scale. If you did more detailed testing, like zooming in a bit using Google Earth (analogous to some types of FISH, maybe), then you would see that Manchester was missing. Even then though there could be a house missing in Manchester (getting down to DNA level now) and you wouldn't possibly notice that unless you knew exactly where to start looking.

I suspect that hasn't helped much, sorry.

I would agree with what all the others have said, basically the results show that the correct number of chromosomes are present and they are all the right size. The commonest chromosomal abnormality likely to cause dev delay is Downs syndrome where there are 3 chromosome 21s instead of two. This will have been the sort of thing they were checking for.So fortunately everything is OK there, however the test will not show small abnormalities within the chromosomes.

Thank you everyone. I like your analogy Tamum. He has been referred to see the Geneticist in the New Year and I guess they will be delving deeper into his chromosomes in the meantime.