Name of the Condition

• Trisomy 21, mosaicism (mitotic nondisjunction)
• Commonly known as Mosaic Down Syndrome

Summary

Mosaic Down Syndrome is a genetic condition where a person has a mix of normal and extra chromosome 21 cells. This occurs due to mitotic nondisjunction, leading to some cells having the usual two copies of chromosome 21, while others have three.

Causes

The condition results from errors during cell division after fertilization, known as mitotic nondisjunction, rather than a uniform chromosomal anomaly present from conception like in standard Down syndrome.

Risk Factors

• Maternal age: Advanced maternal age increases the risk of nondisjunction errors.
• Family history: While not typically inherited, having a sibling with Down syndrome may slightly increase risks.

Symptoms

• Developmental delays
• Intellectual disabilities
• Physical features such as a flat facial profile, almond-shaped eyes, and a single deep crease across the palm
• The severity and presentation of symptoms can vary depending on the percentage of affected cells.

Diagnosis

• Genetic testing such as karyotyping or chromosomal microarray analysis to identify mosaic patterns
• Amniocentesis or chorionic villus sampling during pregnancy may also indicate mosaicism

Treatment Options

• Early intervention programs with physical, occupational, and speech therapy to support development
• Treatment of associated health issues, such as cardiac or respiratory problems, if present
• Educational support to cater to any learning difficulties

Prognosis and Follow-Up

• Many individuals have a relatively typical life expectancy, but with varying degrees of independence and health needs.
• Regular follow-ups to manage developmental progress and health concerns are crucial.

Complications

• Increased risk of heart defects, respiratory issues, and hearing problems.
• Potential for some level of intellectual disability, though typically milder than non-mosaic Down syndrome.

Lifestyle & Prevention

• While prevention of mosaicism isn't possible, lifestyle choices like early prenatal care and consultations can support overall health.
• Parents of affected children should promote a healthy lifestyle, including appropriate nutrition and physical activity.

When to Seek Professional Help

• Concerns about developmental milestones or unusual health issues should prompt consultation with healthcare professionals.

Additional Resources

• The National Down Syndrome Society (NDSS)
• The Down Syndrome Resource Foundation

Tips for Medical Coders

• Ensure clarity when documenting the mosaicism nature of Trisomy 21, distinguishing it from non-mosaic Down syndrome (Q90.0).
• Verify diagnostic confirmation through genetic tests to avoid misclassification.