Are life-threatening chromosomal disorders usually detected in early infancy? would a 2 yo have already shown signs if there is was serious problem?

Usually: Nowadays, any kid who's a little different is likely to be checked for chromosomal microdeletions. A few are well-known and occasionally, as for velofacial cardiac syndrome, forewarned is forearmed; all the gene testing in the world is no substitute for a good physical exam & appropriate imaging. If junior seems otherwise okay, relax & enjoy being a parent of a kid who'll probably be a joy.

Yes: The normal impact of chromosome abnormalities is the interruption of complex fetal organ development. Too many or too few genes change the process.The heart/brain/facial features/hands & feet are all complex & usually show the effects.Some kids escape defects in one area but show them in another. Most are evident within the first months but some less threatening defects can escape early detection.