Down Syndrome: Clinical Case and Viva QnA
Clinical Case of Down Syndrome
A 2-day-old newborn male is referred to the pediatric clinic for evaluation of possible Down syndrome. The infant was born at 38 weeks gestation to a 38-year-old primiparous mother via spontaneous vaginal delivery. Pregnancy was uncomplicated, and prenatal screening tests were declined.
On physical examination, the infant presents with:
- Hypotonia
- Flat facial profile
- Upslanting palpebral fissures
- Small, low-set ears
- Single palmar crease on the right hand
- Increased space between first and second toes (sandal gap)
- Weak Moro reflex
Cardiac auscultation reveals a grade 3/6 systolic murmur, loudest at the left sternal border. Abdominal examination is unremarkable.
A karyotype analysis is ordered, which confirms trisomy 21 (47,XY,+21), establishing the diagnosis of Down syndrome.
5 Varieties of Presentation of Down Syndrome
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Classical Trisomy 21:
- Most common form (95% of cases)
- Characteristic facial features (flat face, upslanting palpebral fissures, small nose)
- Hypotonia
- Intellectual disability
- Congenital heart defects (e.g., atrioventricular septal defect)
-
Mosaic Down Syndrome:
- Milder phenotypic features
- Variable degree of intellectual disability
- May have fewer health complications
- Some cells have trisomy 21, while others have normal karyotype
-
Translocation Down Syndrome:
- Occurs in about 4% of cases
- Extra chromosome 21 material attached to another chromosome (usually 14)
- Can be inherited from a parent with balanced translocation
- Similar physical features to classical trisomy 21
-
Brushfield Spots Variant:
- Prominent white or grayish spots on the iris
- More noticeable in individuals with lighter-colored eyes
- Present in about 85% of individuals with Down syndrome
-
Duodenal Atresia Presentation:
- Presents with bilious vomiting in the neonatal period
- Abdominal distension and failure to pass meconium
- Occurs in approximately 5-7% of infants with Down syndrome
- Requires surgical intervention
Viva QnA
1. What is the genetic cause of Down syndrome?
Down syndrome is caused by the presence of an extra copy of chromosome 21, resulting in trisomy 21. This can occur through non-disjunction during meiosis, mosaic trisomy, or chromosomal translocation.
2. What is the incidence of Down syndrome?
The incidence of Down syndrome is approximately 1 in 700 live births. The risk increases with maternal age, particularly after 35 years.
3. Name three common facial features of Down syndrome.
Three common facial features of Down syndrome are:
- Flat facial profile
- Upslanting palpebral fissures
- Small nose with a flat nasal bridge
4. What is the most common congenital heart defect in Down syndrome?
The most common congenital heart defect in Down syndrome is the atrioventricular septal defect (AVSD), also known as endocardial cushion defect, which occurs in about 40-50% of cases.
5. How is Down syndrome definitively diagnosed?
Down syndrome is definitively diagnosed through chromosomal analysis, typically by karyotyping. This can be done prenatally through amniocentesis or chorionic villus sampling, or postnatally using a blood sample.
6. What is the life expectancy for individuals with Down syndrome?
With modern medical care and early interventions, the life expectancy for individuals with Down syndrome has increased significantly. Many now live into their 60s, with an average life expectancy of around 60 years.
7. What is the risk of developing Alzheimer's disease in individuals with Down syndrome?
Individuals with Down syndrome have an increased risk of developing Alzheimer's disease, with symptoms often appearing in their 40s or 50s. By age 60, about 50-70% of people with Down syndrome show signs of Alzheimer's disease.
8. What is the recommended age for starting thyroid function screening in children with Down syndrome?
Thyroid function screening should begin at birth and be repeated at 6 months, 12 months, and then annually throughout life due to the increased risk of thyroid dysfunction in individuals with Down syndrome.
9. What is the significance of the single palmar crease in Down syndrome?
The single palmar crease, also known as the simian crease, is present in about 45% of individuals with Down syndrome. While it's a characteristic feature, it's not diagnostic as it can also occur in about 1% of the general population.
10. How does maternal age affect the risk of having a child with Down syndrome?
The risk of having a child with Down syndrome increases with maternal age. At age 25, the risk is about 1 in 1,250. At age 35, it increases to 1 in 400, and by age 45, the risk is approximately 1 in 30.
11. What is mosaic Down syndrome?
Mosaic Down syndrome is a less common form where some cells of the body have trisomy 21, while others have the typical 46 chromosomes. This can result in a milder presentation of Down syndrome features and potentially higher cognitive function.
12. What is the recommended frequency of hearing evaluations for children with Down syndrome?
Hearing evaluations should be performed every 6 months until age 3, and then annually thereafter. This is due to the high prevalence of conductive and sensorineural hearing loss in individuals with Down syndrome.
13. What is the association between Down syndrome and leukemia?
Children with Down syndrome have a 10-20 times higher risk of developing leukemia compared to the general population. Acute myeloid leukemia (AML) and acute lymphoblastic leukemia (ALL) are the most common types observed.
14. What is atlantoaxial instability and why is it important in Down syndrome?
Atlantoaxial instability refers to increased mobility between the first and second cervical vertebrae. It occurs in about 15% of individuals with Down syndrome and can potentially lead to spinal cord compression. Regular screening and caution with certain physical activities are recommended.
15. What are Brushfield spots and how often are they seen in Down syndrome?
Brushfield spots are small, white or grayish spots on the iris of the eye. They are seen in about 85% of individuals with Down syndrome who have light-colored eyes, but are less noticeable in those with darker eyes.
16. How does Down syndrome affect cognitive development?
Down syndrome typically causes mild to moderate intellectual disability. However, cognitive abilities can vary widely among individuals. Early intervention programs can significantly improve cognitive outcomes and adaptive skills.
17. What is the recommended approach to growth monitoring in children with Down syndrome?
Children with Down syndrome should be monitored using specific growth charts developed for this population. These charts account for the different growth patterns typically seen in Down syndrome, including shorter stature and increased risk of obesity.
18. What is the prevalence of celiac disease in individuals with Down syndrome?
The prevalence of celiac disease in individuals with Down syndrome is estimated to be 5-15%, which is significantly higher than in the general population. Regular screening for celiac disease is recommended, starting at age 2-3 years.
19. What are the main features of the cardiovascular system assessment in a newborn with Down syndrome?
The cardiovascular assessment should include:
- Careful auscultation for murmurs
- Evaluation of peripheral pulses
- Assessment for cyanosis or tachypnea
- Echocardiogram within the first month of life, even in the absence of murmurs
20. What is the recommended ophthalmological follow-up for children with Down syndrome?
Children with Down syndrome should have:
- Initial eye examination by 6 months of age
- Annual examinations from age 1 to 5 years
- Every 2 years after age 5
21. How does Down syndrome affect the immune system?
Down syndrome is associated with various immune system abnormalities, including:
- Reduced number and function of T and B lymphocytes
- Decreased neutrophil chemotaxis
- Increased susceptibility to infections
- Higher risk of autoimmune disorders
22. What is the significance of duodenal atresia in Down syndrome?
Duodenal atresia occurs in approximately 5-7% of infants with Down syndrome. It presents with bilious vomiting and abdominal distension in the neonatal period. The association is important because the presence of duodenal atresia should prompt evaluation for Down syndrome, and vice versa.
23. What are the main speech and language challenges in Down syndrome?
Individuals with Down syndrome often experience:
- Delayed language acquisition
- Difficulties with speech articulation
- Stronger receptive language compared to expressive language
- Challenges with complex sentence structures
24. How does sleep apnea affect individuals with Down syndrome?
Obstructive sleep apnea is common in Down syndrome due to anatomical factors like midface hypoplasia, macroglossia, and hypotonia. It can lead to:
- Daytime sleepiness
- Behavioral issues
- Cognitive impairment
- Cardiovascular complications
25. What prenatal screening methods are available for Down syndrome?
Prenatal screening methods for Down syndrome include:
- First trimester combined test (nuchal translucency ultrasound and serum markers)
- Second trimester quadruple screen
- Non-invasive prenatal testing (NIPT) using cell-free fetal DNA
- Diagnostic tests like chorionic villus sampling and amniocentesis for definitive diagnosis
