Genetics · MU Sofia

51. Congenital anomalies – classification and Etiology. Dysmorphology and teratogenesis.

Covers the definition and frequency of congenital anomalies, then sets out how they are classified by pathogenetic mechanism (malformations, deformations, disruptions, dysplasias) and by morphology (major and minor). It goes on to genetic and environmental causes, Wilson's principles of teratogenesis with a table of critical periods, and the main physical, chemical, biological and maternal teratogens. It closes with dysmorphology concepts such as syndrome, sequence and association, and with primary and secondary prevention.

Inside: 7 sections · 13 labelled pictures · 1 table · 14 flashcards · 4 min

Topic 51 of 65 in the MU Sofia syllabus for Genetics (Medicine, Year 3). The free AceMed note covers it in 7 sections, about 579 words (4 min of reading), with 14 flashcards.

In this note

  1. Congenital anomalies – classification and Etiology. Dysmorphology and teratogenesis.
  2. II. CLASSIFICATION OF CONGENITAL ANOMALIES
  3. III. ETIOLOGY OF CONGENITAL ANOMALIES
  4. IV. TERATOGENESIS
  5. V. TYPES OF TERATOGENS
  6. VI. DYSMORPHOLOGY
  7. VII. PREVENTION OF CONGENITAL ANOMALIES

Congenital anomalies – classification and Etiology. Dysmorphology and teratogenesis.

Congenital anomalies (also called congenital malformations or birth defects) are structural, functional, or metabolic abnormalities that are present at birth, although they may become clinically apparent later in life.

They arise due to disturbances in prenatal development, particularly during embryogenesis.

Epidemiology

  • Occur in approximately 2–4% of live births
  • Major cause of:
  • infant mortality,
  • childhood disability,
  • long-term morbidity

II. CLASSIFICATION OF CONGENITAL ANOMALIES

Congenital anomalies can be classified based on pathogenetic mechanism, morphology, or etiology.

A. Classification According to Pathogenetic Mechanism

1. Malformations

Malformations are primary structural defects caused by intrinsic developmental errors during organ formation (organogenesis).

Key points:

  • Occur early (3rd–8th week of gestation)
  • Usually genetically determined

Examples:

  • Neural tube defects
  • Congenital heart defects
  • Cleft lip and palate

2. Deformations

Deformations result from mechanical forces acting on a normally developing fetus, leading to abnormal shape or position.

Key points:

  • Occur later in pregnancy
  • Often reversible

Examples:

  • Clubfoot due to uterine constraint
  • Hip dislocation
  • Cranial molding

3. Disruptions

Disruptions are defects caused by destruction of previously normal tissue.

Key points:

  • Extrinsic cause
  • Sudden onset

Examples:

  • Limb defects due to amniotic bands
  • Intestinal atresia due to vascular accidents

4. Dysplasia

Dysplasia refers to abnormal cellular organization within tissues, usually affecting an entire tissue type.

Key points:

  • Often genetic
  • Progressive

Examples:

  • Skeletal dysplasias
  • Ectodermal dysplasia

B. Classification According to Morphology

1. Major Anomalies

  • Cause significant functional impairment or cosmetic deformity
  • Often require medical or surgical treatment

Examples:

Congenital heart defects, neural tube defects

2. Minor Anomalies

  • Minimal functional impact
  • Often markers of underlying syndromes

Examples:

Low-set ears, epicanthic folds, single palmar crease

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