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Fetopathology and developmental pathology of the embryo and fetus
Marta Ježová, Josef Feit et al.
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Single gene disorders
Introduction

Single gene disorders (mendelian disorders) involve approximately 0.6 – 0.8 % of general population. They are passed from generation to generation according to the Mendel's laws. 90% are inherited in autosomal manner (dominant or recessive), 10% are inherited in X-linked manner.

Classification

Types of heredity:

  • autosomal dominant heredity:
    • is the most frequent
    • male : female ratio is 50 : 50
    • 50% descendents are affected, 50% are healthy
    • characteristic is variable expresivity a penetration of the pathological gene
    • examples: Marfan's syndrome, tuberous sclerosis, achondroplasia
  • autosomal recessive heredity:
    • clinical symptoms are manifested only in homozygotes
    • 25% descendents are affected, 50% are carriers, 25% are healthy
    • many of the autosomal recessive disorders are enzymopathies — enzyme defects
    • examples: mucoviscidosis, phenylketonuria, Wilson's disease
  • gonosomal heredity:
    • X-linked
    • almost always recessive
    • most of the affected are males
    • examples: Duchenne's muscular dystrophy, hemophilia
Tuberous sclerosis