Congenital Anomalies and Dysmorphic Features

Introduction

Congenital anomalies and dysmorphic features are critical topics for the MCCQE1 exam and Canadian medical practice. This comprehensive guide will help you prepare for the Canadian medical licensing exam by covering key concepts, Canadian guidelines, and providing MCCQE1-style practice questions.

Definition and Epidemiology

Congenital anomalies are structural or functional abnormalities present at birth. Dysmorphic features are physical characteristics that deviate from the normal pattern of development.

Canadian Epidemiology

• Congenital anomalies affect approximately 3-5% of newborns in Canada
• They are a leading cause of infant mortality, accounting for 23% of infant deaths in Canada
• The prevalence varies among different ethnic groups within Canada's diverse population

Types of Congenital Anomalies

Congenital anomalies can be classified into several categories:

1. Structural anomalies: Affect the formation of body parts
2. Functional anomalies: Affect how body systems work
3. Metabolic disorders: Affect chemical processes in the body
4. Chromosomal abnormalities: Result from changes in chromosome number or structure

Common Dysmorphic Features

Understanding dysmorphic features is essential for recognizing potential genetic syndromes. Here are some common features to look for:

• Facial anomalies (e.g., hypertelorism, low-set ears)
• Limb abnormalities (e.g., polydactyly, syndactyly)
• Growth abnormalities (e.g., short stature, macrocephaly)
• Skin abnormalities (e.g., café-au-lait spots, hypopigmentation)

Diagnostic Approach

When evaluating a patient with suspected congenital anomalies or dysmorphic features, follow these steps:

Canadian Guidelines for Screening and Management

The Canadian College of Medical Geneticists (CCMG) and the Society of Obstetricians and Gynaecologists of Canada (SOGC) provide guidelines for genetic screening and management of congenital anomalies.

Key points include:

1. Universal offer of prenatal screening for common aneuploidies
2. Non-invasive prenatal testing (NIPT) as an option for high-risk pregnancies
3. Newborn screening programs for metabolic and genetic disorders (varies by province)
4. Multidisciplinary approach to management of congenital anomalies

Key Syndromes for MCCQE1

Familiarize yourself with these commonly tested syndromes:

1. Down syndrome (Trisomy 21)

   • Most common chromosomal abnormality
   • Features: Hypotonia, flat facial profile, upslanting palpebral fissures

2. Turner syndrome (45,X)

   • Affects females
   • Features: Short stature, webbed neck, shield chest

3. Marfan syndrome

   • Autosomal dominant connective tissue disorder
   • Features: Tall stature, arachnodactyly, lens dislocation

4. Fetal Alcohol Spectrum Disorder (FASD)

   • Caused by prenatal alcohol exposure
   • Features: Growth deficiency, central nervous system abnormalities, facial dysmorphism

Management Principles

Management of congenital anomalies and dysmorphic features in Canada follows these principles:

1. Early detection and intervention
2. Multidisciplinary care coordination
3. Family-centered approach
4. Long-term follow-up and support
5. Integration with community resources

Key Points to Remember for MCCQE1

• 🍁 Understand the Canadian epidemiology of congenital anomalies
• 🍁 Know the Canadian guidelines for prenatal and newborn screening
• 🍁 Recognize common dysmorphic features and their associated syndromes
• 🍁 Be familiar with the diagnostic approach, including genetic testing options available in Canada
• 🍁 Understand the principles of management and the role of multidisciplinary care in the Canadian healthcare system
• 🍁 Be prepared to discuss ethical considerations in genetic counseling and testing

Sample Question

A 28-year-old woman presents to her family physician at 10 weeks gestation for her first prenatal visit. She has no significant medical history and takes no medications. Her family history is negative for genetic disorders. Which one of the following prenatal screening options is most appropriate to offer this patient according to Canadian guidelines?

• A. Chorionic villus sampling
• B. Amniocentesis
• C. Non-invasive prenatal testing (NIPT)
• D. Maternal serum screening
• E. No screening is necessary

Explanation

The correct answer is:

• D. Maternal serum screening

Explanation: According to Canadian guidelines, all pregnant women should be offered prenatal screening for common aneuploidies, regardless of age or risk factors. For a low-risk pregnancy at 10 weeks gestation, maternal serum screening is the most appropriate first-line screening option.

• Option A (Chorionic villus sampling) and B (Amniocentesis) are invasive procedures typically reserved for high-risk pregnancies or for diagnostic confirmation after positive screening results.
• Option C (NIPT) is not routinely offered as first-line screening in Canada for low-risk pregnancies due to cost considerations, although it may be available as an option.
• Option E is incorrect because offering prenatal screening is standard of care in Canada.

References

1. Langlois, S., & Brock, J. A. (2013). Current status in non-invasive prenatal detection of Down syndrome, trisomy 18, and trisomy 13 using cell-free DNA in maternal plasma. Journal of Obstetrics and Gynaecology Canada, 35(2), 177-181.

2. Rasmussen, S. A., & Friedman, J. M. (2012). The etiology of congenital anomalies: Where are we now? American Journal of Medical Genetics Part C: Seminars in Medical Genetics, 157C(2), 127-133.

3. Public Health Agency of Canada. (2019). Congenital Anomalies in Canada 2017. Ottawa: Public Health Agency of Canada.

4. Canadian College of Medical Geneticists. (2018). Practice Guidelines for the Detection, Diagnosis, and Management of Genetic Disorders. Retrieved from https://www.ccmg-ccgm.org/practice-guidelines (opens in a new tab)

5. Society of Obstetricians and Gynaecologists of Canada. (2017). Prenatal Screening for Fetal Aneuploidy in Singleton Pregnancies. Journal of Obstetrics and Gynaecology Canada, 39(9), e380-e394.