Is downs syndrome an inborn error of metabolism?

Extrachromosome: Down syndrome is due to one extra copy of chromosome number 21, trisomy 21. It is not due to a single gene defect affecting metabolism of one entity.

Maybe: The classic inborn errors are genetic defects in single genes that code for enzymes that help turn your food into you. Down syndrome is due to having 3 copies of an entire chromosome, #21, that contains hundreds of genes. There is early evidence that a "gene dosage effect" does alter some steps in metabolism in Down syndrome because the genes for some metabolic enzymes are on chromosome 21.