Cytology · MU Sofia

Chromosomal and genetic defects underlying congenital malformations.

Covers chromosomal and genetic causes of congenital malformations, starting with numerical defects such as trisomies 21, 18 and 13, monosomy X and polyploidy, then structural changes like deletions, duplications, translocations and microdeletions. It moves on to single-gene disorders grouped by inheritance pattern, multifactorial conditions such as neural tube defects and cleft lip, and epigenetic changes, before ending with how these errors disturb early development. Clinical features of each named syndrome are given alongside.

Inside: 4 sections · 11 labelled pictures · 14 flashcards · 4 min

Topic 95 of 97 in the MU Sofia syllabus for Cytology (Medicine, Year 1). The free AceMed note covers it in 4 sections, about 530 words (4 min of reading), with 14 flashcards.

In this note

  1. Introduction
  2. Chromosomal Defects
  3. Genetic Defects
  4. How These Defects Affect Development

Introduction

Congenital malformations, or birth defects, arise from a variety of genetic and environmental factors and can be categorised based on their type, cause, or the body systems they affect. These malformations can manifest due to chromosomal defects, genetic mutations, multifactorial inheritance, and epigenetic changes.

Chromosomal Defects

  • These defects involve alterations in the number or structure of chromosomes, which carry genetic instructions for development.
  • Numerical abnormalities include changes in the number of chromosomes:
  • Trisomy occurs when there is an extra chromosome.
  • Trisomy 21 (Down Syndrome): An extra chromosome 21 leads to intellectual disability, heart defects, and distinct facial features.
  • Trisomy 18 (Edwards Syndrome): An extra chromosome 18 causes severe growth problems, organ defects, and a high mortality rate.
  • Trisomy 13 (Patau Syndrome): An extra chromosome 13 results in brain defects, cleft palate, and heart malformations.
  • Monosomy occurs when there is a missing chromosome.
  • Turner Syndrome (45, X): In females, the absence of one X chromosome leads to short stature, infertility, and some developmental delays.
  • Polyploidy is the presence of extra sets of chromosomes, which usually results in miscarriage (e.g., triploidy).
  • Structural abnormalities involve changes in the structure of chromosomes:
  • Deletions: A part of a chromosome is missing.
  • Cri-du-chat Syndrome (chromosome 5 p arm deletion): Causes a cat-like cry in infants, intellectual disability, and a small head size.
  • Duplications: Extra copies of chromosome sections are present, which can cause developmental delays and organ abnormalities.
  • Translocations: Parts of one chromosome attach to another. For example, some cases of familial Down syndrome involve translocations between chromosomes 21 and 14.
  • Microdeletions/Microduplications: Tiny pieces of chromosomes are either missing or extra. For instance, 22q11.2 Deletion Syndrome (DiGeorge Syndrome) can cause heart defects, immune system problems, and cleft palate.

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