The degree of the medical problems and disability can vary widely in children with a related disorder because the genetic material that is extra or missing will be different in every case, and the professional opinion of a clinical geneticist should always be sought.
In mosaicism there is an extra chromosome in some cells but other cells have normal chromosomes. The cells with 45 chromosomes die. Some children may be profoundly handicapped, but many are much lesser affected, and several SOFT children with mosaicism have entered mainstream education.
In a partial trisomy there is a small extra piece of a chromosome attached to another chromosome. This may be called an unbalanced translocation. A deletion means that there is part of a chromosome missing. The long arm of the chromosome is referred to as q and the short arm as p. A deletion of one of the long arms of chromosome 13 would be 13q-, and numbers can be used to specify exact areas of the chromosome.
In some rare cases chromosomes can form rings due to a loss of genetic material from both ends of the chromosome. Cell divisions during the development of the embryo, foetus, child, and adult, may involve further damage to the ring chromosome, and generally this cell division happens at a lower rate and body growth is slowed.
Holoprosencephaly is when the front part of the brain fails to develop into clearly separate right and left halves, and although a baby with holoprosencephaly may have normal chromosomes, it is common in trisomy 13. This may severely affect the function of the brain, although among children with this condition there is considerable variability in the degree of malformation and its effects. Babies diagnosed with this condition usually have a small head, excessive fluid in the brain, cleft lip, varying degrees of learning difficulties, epilepsy, hormonal problems, or problems with the heart, bones, bowel or bladder.