Monosomy 21 is a rare chromosomal disorder in which a person is missing the entire 21st chromosome. This condition is also known as trisomy 21 or Down syndrome. People with monosomy 21 have a wide range of physical and mental disabilities, including intellectual disability, developmental delays, and physical abnormalities.

The most common symptoms of Monosomy 21 (also known as Trisomy 21 or Down Syndrome) include:

- Low muscle tone
- Small stature
- Flattened facial features
- Upward slanting eyes
- Short neck
- Poor coordination
- Delayed development
- Intellectual disability
- Congenital heart defects
- Hearing and vision problems
- Increased risk of infections

Monosomy 21, also known as Trisomy 21 or Down Syndrome, is caused by an extra copy of chromosome 21. This extra copy of chromosome 21 is usually caused by a random error in cell division during the development of the egg or sperm. It can also be caused by a parent passing on an extra copy of chromosome 21 to their child.

Monosomy 21, also known as Trisomy 21 or Down Syndrome, is a genetic disorder caused by the presence of an extra copy of chromosome 21. Treatment for Monosomy 21 is focused on managing the physical and intellectual disabilities associated with the condition. Treatment may include physical, occupational, and speech therapy, as well as medications to help manage symptoms. Other treatments may include special education, social skills training, and behavior modification. In some cases, surgery may be recommended to correct physical abnormalities.

1. Advanced maternal age: Women over the age of 35 are more likely to have a baby with monosomy 21.

2. Previous pregnancy with trisomy 21: Women who have had a previous pregnancy with trisomy 21 are more likely to have a baby with monosomy 21.

3. Family history of monosomy 21: If a family member has had monosomy 21, the risk of having a baby with monosomy 21 is increased.

4. Abnormal prenatal screening results: Abnormal results on prenatal screening tests can indicate an increased risk of monosomy 21.

5. Abnormal ultrasound results: Abnormal results on an ultrasound can indicate an increased risk of monosomy 21.

There is no cure for Monosomy 21 (also known as Down Syndrome). However, there are medications and therapies that can help manage the symptoms associated with the condition. These include medications to help with cognitive and behavioral issues, physical therapy to help with motor skills, and speech therapy to help with communication.