What is the best explanation of a child having the physical phenotype of Down syndrome but having a totally normal karyotype on chromosomal analysis of blood?

Down Syndrome

Explanation:

Individuals who acquire an unequal translocation including chromosome 21 may have extra hereditary material from chromosome 21, which causes Down Syndrome.  Trisomy 21, mosaic Down Syndrome isn't acquired. It happens as an arbitrary occasion during cell division right off the bat in fetal improvement.  The most widely recognized type of Down Syndrome is called trisomy 21. This is a condition wherein individuals have 47 chromosomes in every cell rather than 46. A blunder in cell division called nondisjunction causes trisomy 21. This mistake leaves a sperm or egg cell with an additional duplicate of chromosome 21 preceding or at origination.  Around 95 percent of the time, Down disorder is brought about by trisomy 21  the individual has three duplicates of chromosome 21, rather than the standard two duplicates, in all cells. This is brought about by anomalous cell division during the advancement of the sperm cell or the egg cell.  Trisomy 18 and 13 are normally brought about by unconstrained hereditary changes that happen at the hour of preparation.Each egg and sperm cell contains 23 chromosomes. The association of these cells makes 23 sets, or 46 complete chromosomes, half from the mother and half from the father.