Implications of abnormal 21 karyotype

46xy,inv(21)(q11.qq22.3)

I hope there is someone out there who can give me some insight into what this particular karyotype means.

My six-year old grandson is developmentally delayed. Assessments have placed him at the emotional level of a 3-4 year old with severely delayed gross and fine motor skills. He is currently finishing grade 1 and is able to read at a lower level, but has great difficulty with printing, drawing shapes, and coloring and is far behind his classmates in all areas. He can follow complex directions. He can also navigate well on the computer and is pretty good at understanding and playing video games, but has trouble with cooperative play and rules. His vocabulary is adequate, but he has slurred speech and can be difficult to understand. Physically, he is average height and quite slender with very poor muscle tone. He has a distinctly awkward gait and has difficulty determining spatial relations and body positioning. His facial features are slightly dysmorphic - broad forehead, wideset eyes, heavy jaw - and he has difficulty chewing and swallowing. He has frequent asthma attacks that require hospitalization. Although he is at times frustrated by his limitations (the mind is willing but the body is weak), he is a sweet, loving and thoughtful boy.

He has been undergoing assessments to determine the extent and long-term implications of his disabilities. All of his biological tests came back normal except for the karyotype, which indicated an abnormality - inv(21)(q11qq22.3). I understand that and extra copy of chromosome 21 causes Downs Syndrome, but what exactly does particular notation mean?

We have so many questions. Is this simply a 'delay' in development? Will he catchup, or will he reach a certain point and not progress further? What are the long-term mental and physical health implications associated with abnormalities on this chromosome (i.e., Alzheimer's, nervous disorders, cancers, or other medical problems)?

His follow-up appointment to discuss these results is not scheduled until August. In the meantime, we have to deal with his teachers and the school board to determine a suitable program for him next fall. We know he should be held back, but at the same time, it would be crushing for him to see another group of children move past him in the system next year. The school will not assign a classroom aide or developmental curriculum without a clear diagnosis. We would like to have at least some interpretation of these results in order to press for the special consideration he needs to succeed at school.

Any insight would be most appreciated.