Which one affects the other, Down syndrome or hypothyroidism?

Patient's question:

Very thin and very worried, don't know what to do. Please ask the doctor to explain it well, we don't know which hospital to believe anymore! Thank you! Down Syndrome Examination Report; Chromosome number: 47 cells: 15 autosomes: 45 sex chromosomes 2 karyotype analysis: 47, XY, +21

Doctor's answer:

Congenital hypothyroidism should be diagnosed early and treated as soon as possible to minimize damage to brain development. Once the diagnosis is confirmed, lifelong thyroid hormone replacement therapy should be taken without interruption, otherwise, all previous efforts will be wasted. The diet should be rich in protein, vitamins, and minerals. Down syndrome has no effective treatment methods. Hypothyroidism does not cause Down syndrome either.