In simple words: This code represents the most common type of Down syndrome, where a person has an extra copy of chromosome 21 due to a cell division error during reproduction. This results in various physical characteristics and developmental differences.

Trisomy 21, nonmosaicism (meiotic nondisjunction) is a genetic condition where an individual has three copies of chromosome 21 instead of the usual two. This occurs due to an error in cell division called nondisjunction during meiosis, the process of forming reproductive cells (sperm and egg).It's the most common form of Down syndrome.

Example 1: A newborn infant exhibits characteristic features of Down syndrome, including hypotonia, a flat facial profile, and upward-slanting eyes. Karyotyping confirms the presence of trisomy 21 due to meiotic nondisjunction. The diagnosis is coded as Q90.0., A prenatal screening test indicates a high risk of Down syndrome. Subsequent diagnostic testing, such as amniocentesis or chorionic villus sampling, confirms trisomy 21 due to nonmosaicism (meiotic nondisjunction). This would be coded as Q90.0. , A young child with developmental delays and characteristic physical features of Down syndrome is being evaluated by a specialist. Genetic testing confirms the diagnosis of trisomy 21 resulting from meiotic nondisjunction, therefore Q90.0 is used.

Documentation for Q90.0 should include results of chromosomal analysis (karyotype) confirming the diagnosis of trisomy 21.Clinical findings consistent with Down syndrome, such as hypotonia, characteristic facial features, and developmental delays, should also be documented.

** This code is specifically for Trisomy 21 caused by meiotic nondisjunction and not for mosaic Trisomy 21 or other chromosomal abnormalities. Use additional codes to specify any associated conditions, such as congenital heart defects or intellectual disabilities.