Down Syndrome (Trisomy 21) Animation | Causes, Features & Clinical Insights for NEET PG & USMLE

Summary

This video explains Down syndrome (Trisomy 21), a genetic condition caused by an extra chromosome 21, leading to physical traits, intellectual disabilities, and various medical challenges. The video covers its causes, including nondisjunction, Robertsonian translocation, and mosaicism, as well as risk factors like maternal age. Key features include distinct facial characteristics, heart defects, gastrointestinal issues, and an increased risk of early-onset dementia and leukemia. Prenatal diagnosis and early intervention through therapy and surgery can significantly improve outcomes, allowing individuals with Down syndrome to live fulfilling lives.

Takeaways

• 😀 Down syndrome, also known as Trisomy 21, is a genetic condition caused by an extra copy of chromosome 21.
• 😀 The most common cause of Down syndrome is complete trisomy, where every cell in the body has an extra chromosome 21 due to nondisjunction during egg or sperm formation.
• 😀 A small percentage of Down syndrome cases (4%) are caused by Robertsonian translocation, which can be inherited, requiring genetic counseling.
• 😀 Mosaicism, accounting for about 1% of cases, occurs when some cells have an extra chromosome 21 while others do not, potentially leading to milder symptoms.
• 😀 Advanced maternal age, especially women over 35, significantly increases the risk of having a child with Down syndrome due to age-related changes in egg cells.
• 😀 Common physical traits in children with Down syndrome include distinct facial features, such as Brushfield spots, epicanthal folds, a flat nasal bridge, and a protruding tongue.
• 😀 Children with Down syndrome often have intellectual disabilities ranging from mild to moderate and may have a single transverse palmar crease and a wide gap between the first and second toes.
• 😀 Congenital heart defects, such as AVSD (Atrioventricular Septal Defect), are common in children with Down syndrome and may require surgical intervention.
• 😀 Gastrointestinal issues like duodenal atresia, imperforate anus, and Hirschsprung disease are seen in some Down syndrome patients, requiring careful management.
• 😀 Individuals with Down syndrome are at a higher risk of developing early-onset dementia, leukemia, hypothyroidism, and immune system dysfunction.
• 😀 Early intervention therapies, including speech, physical, and occupational therapy, play a critical role in helping individuals with Down syndrome develop essential skills for independence and quality of life.

Q & A

What is Down syndrome and how does it occur?

Down syndrome, also known as Trisomy 21, is a genetic condition caused by an extra copy of chromosome 21. This additional genetic material disrupts normal growth and development, leading to intellectual disabilities, distinct physical traits, and certain medical challenges.

What is the most common cause of Down syndrome?

The most common cause of Down syndrome, seen in about 95% of cases, is complete trisomy 21. This occurs due to an error during the formation of eggs or sperm, a process known as nondisjunction, where one cell has an extra chromosome 21.

What is a Robertsonian translocation and how does it relate to Down syndrome?

A Robertsonian translocation occurs in about 4% of Down syndrome cases. It involves part of chromosome 21 attaching to another chromosome, such as chromosome 14. This form can be inherited, and parents may need genetic counseling.

What is mosaicism in relation to Down syndrome?

Mosaicism accounts for about 1% of Down syndrome cases. In this form, some cells have an extra chromosome 21 while others do not, leading to milder features depending on the proportion of affected cells.

How does advanced maternal age impact the risk of having a child with Down syndrome?

Women over 35 have a significantly higher chance of having a child with Down syndrome due to age-related changes in egg cells. At age 40, the risk is about 1 in 100, compared to 1 in 700 for women under 30.

What are the typical physical features of a child with Down syndrome?

Children with Down syndrome often have distinct facial features, including brushfield spots (small white spots on the iris), epicanthal folds, a flat nasal bridge, and a protruding tongue. They also have a single transverse palmar crease and a wide gap between the first and second toes.

What are some common medical conditions associated with Down syndrome?

Children with Down syndrome may have congenital heart defects, gastrointestinal issues (like duodenal atresia and imperforate anus), early-onset dementia, leukemia, hypothyroidism, atlantoaxial instability, and increased susceptibility to infections.

How does Down syndrome impact the gastrointestinal system?

Around 5% of children with Down syndrome have gastrointestinal issues like duodenal atresia, which can block the small intestine, and other conditions such as imperforate anus and Hirschsprung disease, which causes severe constipation.

What neurological issues are commonly seen in individuals with Down syndrome?

Individuals with Down syndrome are at an increased risk of early-onset dementia, typically by the age of 40, due to the overexpression of the amyloid precursor protein gene located on chromosome 21, which leads to amyloid plaques and neurofibrillary tangles in the brain.

How is Down syndrome diagnosed and what screening options are available?

Down syndrome is typically diagnosed prenatally via ultrasound (to detect increased nuchal translucency), amniocentesis, or chorionic villus sampling. A quad-screen blood test between 16 and 20 weeks can also help identify pregnancies at risk.