Neurological Balance and Medical Disorders
Authored by: The DrSensory Editorial Team
Reviewed by: 🛡️ DrSensory Clinical Review Board
Last updated: June 2026
Key Takeaways
- Down syndrome is a genetic condition caused by an extra copy of chromosome 21, which disrupts typical development and leads to characteristic physical features and health concerns.
- There are three primary types: trisomy 21 (the most common, about 95% of cases), translocation (about 3%), and mosaic Down syndrome (about 2%).
- Down syndrome usually results from a random error during cell division and is not typically inherited; while women aged 35 and older have a higher risk, most children with Down syndrome are born to mothers under 35.
- Common characteristics include poor muscle tone (hypotonia) and loose joints, delayed speech and language, and mild to moderate intellectual disability, alongside strengths in social interaction and visual learning.
- Every individual with Down syndrome is unique, and early intervention and supportive care can significantly enhance quality of life.
| Trait | Down Syndrome | Autism Spectrum Disorder |
|---|---|---|
| Eye contact | Typically strong | Often reduced |
| Social interest | Often very engaging | May be socially withdrawn |
| Language delay | Present in both | Often more profound in ASD |
| Repetitive behaviors | Less common | Common in ASD |
| Age | Milestone Category | Expected Timeline (with DS) |
|---|---|---|
| 0-3 mo | Lifting head | 6-10 weeks |
| 4-6 mo | Rolling over | 5-7 months |
| 6-10 mo | Sitting unassisted | 9-12 months |
| 12-18 mo | Crawling | 12-18 months |
| 18-24 mo | Walking independently | 18-30 months |
| 2-3 yrs | First words | 2-3 years |
| 3-5 years | Simple sentences | 3-5 years |
Frequently Asked Questions
What causes Down syndrome?
Down syndrome is caused by an extra copy of chromosome 21. It typically arises from a random error during cell division, and while the exact cause is unknown, it is not usually inherited.
What are the different types of Down syndrome?
There are three primary types. Trisomy 21 is the most common at about 95% of cases, translocation occurs in approximately 3% of individuals, and mosaic Down syndrome is a rare form affecting about 2%.
Does the mother's age affect the chance of having a baby with Down syndrome?
Women aged 35 and older have a higher risk. However, the majority of children with Down syndrome are born to mothers under 35 because of higher birth rates in that group.
What are some common signs of Down syndrome in a child?
Common characteristics can include a flattened face, almond-shaped eyes that slant upward, poor muscle tone and loose joints, shorter-than-average height, delayed speech and language, and mild to moderate intellectual disability. Each individual is unique, so the presence and severity of these traits can vary widely.
How is Down syndrome diagnosed?
Diagnosis can occur during pregnancy or after birth. Screening tests assess the likelihood of Down syndrome but are not definitive, while diagnostic procedures such as amniocentesis or chorionic villus sampling (CVS) confirm the presence of an extra chromosome 21.
