Down syndrome (trisomy 21) - causes, symptoms, diagnosis, & pathology

Summary

The video explains the genetic basis of Down syndrome, detailing how it arises from chromosomal abnormalities, specifically an extra copy of chromosome 21. It discusses the process of meiosis and nondisjunction, which can lead to conditions like trisomy 21. Additionally, it touches on Robertsonian translocation as a rare cause and introduces the concept of mosaicism. The video also highlights common physical traits and health issues associated with Down syndrome, emphasizing the impact of maternal age on risk. Despite challenges, it concludes with a hopeful note on the improved quality of life for individuals with Down syndrome.

Takeaways

• 😀 Humans have 46 chromosomes organized into 23 pairs, inherited equally from both parents.
• 😀 Down syndrome, or trisomy 21, is caused by an extra copy of chromosome 21, resulting in 47 chromosomes.
• 😀 Nondisjunction is the primary cause of Down syndrome, occurring when chromosomes fail to separate properly during meiosis.
• 😀 The meiosis process reduces the chromosome number in sex cells from 46 to 23 through two rounds of cell division.
• 😀 Robertsonian translocation, which involves chromosome 21 attaching to another chromosome, accounts for about 4% of Down syndrome cases.
• 😀 Mosaic Down syndrome occurs when some cells have 46 chromosomes while others have 47, affecting about 1% of individuals with Down syndrome.
• 😀 Individuals with Down syndrome may experience various health issues, including heart defects and gastrointestinal problems.
• 😀 Maternal age significantly impacts the risk of having a child with Down syndrome, with higher risks associated with older mothers.
• 😀 Screening tests during pregnancy, like blood tests and ultrasounds, can assess the risk of Down syndrome but are not definitive diagnoses.
• 😀 Advances in medical care have improved the longevity and quality of life for individuals with Down syndrome, allowing many to thrive.

Q & A

What is the basic structure of human DNA?

Human DNA is organized into 46 chromosomes, which are packaged into pairs, with one chromosome from each parent.

What is Down Syndrome and how does it occur?

Down Syndrome, also known as trisomy 21, occurs when an individual has an extra copy of chromosome 21, resulting in a total of 47 chromosomes instead of the usual 46.

What is meiosis and why is it important?

Meiosis is the process that produces sex cells (sperm and egg) and reduces the chromosome number by half, ensuring genetic diversity in offspring.

What is nondisjunction and how does it contribute to chromosomal disorders?

Nondisjunction is the failure of chromosomes to separate properly during cell division, which can result in cells with an abnormal number of chromosomes, such as in Down Syndrome.

How does Robertsonian translocation relate to Down Syndrome?

Robertsonian translocation can lead to Down Syndrome when part of chromosome 21 attaches to another chromosome, typically chromosome 14, leading to genetic abnormalities.

What percentage of Down Syndrome cases are caused by nondisjunction?

About 95% of Down Syndrome cases are due to nondisjunction, while approximately 4% are related to Robertsonian translocation.

What are some common physical characteristics of individuals with Down Syndrome?

Common physical characteristics include a flat facial profile, a simian crease in the hands, and epicanthal folds.

What role does maternal age play in the risk of having a child with Down Syndrome?

Maternal age is a major risk factor; the likelihood of Down Syndrome increases significantly for mothers over 45, with rates of about 1 in 25 births.

What screening tests can be performed during pregnancy to assess the risk of Down Syndrome?

Screening tests include measuring levels of alpha-fetoprotein (AFP), unconjugated estriol (uE3), human chorionic gonadotropin (hCG), and ultrasound to check for nuchal translucency.

How has medical care improved the lives of individuals with Down Syndrome?

Improved medical care has significantly increased the longevity and quality of life for individuals with Down Syndrome, enabling many to thrive and lead fulfilling lives.