Congenital and Genetic abnormalities


Congenital abnormalities


  1. due to developmental error during fetal development

  2. almost always detected at birth

 Developmental processes are occur at a rapid rate therefore errors have devastating implications

Stem cells differentiate into their specialized cell types, move to area of organ or tissue placement then divide.


Errors in embryogenesis – if they occur at the particular organs critical period in development that organ will be severely development


Different structures devel @ different times


Organogensis – begins at day 15 post conception therefore this is the most vulnerable time for mutations.


  • each organ has its own critical period within fetal development – different organs develop at different times

  • The CNS has an extensive critical period therefore most congenital abnormalities will also affect the CNS


Tatatogens: Mutagenic agents

  • drugs

  • microbes

  • vitamin,mineral or nutrient deficiency


Taratogens: – agents that affect the fetal development environment

  • the maternal body

  • the environment outside the maternal body


  1. Falitamide:a taratogen causing limb reduction defects

  2. Alcohol: causes Fetal alcohol Syndrome

  3. Deficiency: Vitamin, mineral or nutrients eg folic acid

  4. Viral infections: eg Rubella virus causing german measles


Fig. gestational development


Genetic Abnormalities


  • Not always present at birth

  • genetic code mutations

eg diabetes


autosomal dominant and recessive


Homozygous for a particular gene when identical alleles of the gene are present on both homologous chromosomes.


Heterozygous for a particular gene when two different alleles occupy the gene’s position on the homologous chromosomes.


Types of Chromosomes

  1. autosomal chromosomes 22 pairs

  2. sex chromosomes –1 pair, 2 chromosomes the X and Y


3 primary types of abnormalities


  1. Chromosomal Abnormalities

  • reflects an atypical number of chromosomes or a structural abnormality in one or more chromosomes.

  • Trisomy 21 – Downs Syndrome


  1. Single gene (monogenic) Chromosomal Abnormalities

2a. autosomal recessive

  • 25% chance of the individual being affected

  • 50% of individuals will be carriers for the gene

  • 25% of individuals will be unaffected

  • Cystic Fibrosis


    2b. autosomal dominant

  • 25% of individuals will be carriers for the gene

  • 50% chance of inheritance

  • 25% will be lethals (noncompatoible with life)

  • Dwarfism


    2c.X-linked recessive

  • the mutated affected gene is linked to the X chromosome

  • hemophilia


  1. Complex trait (polygenic and environmental) Chromosomal Abnormalities

  • type 2 diabetes

  • more than one gene is affected

  • lifestyle (enviro factors)



  1. Chromosomal abnormalities

Numeric abnormalities:


  • Aneuploidy – extra or missing Chromosome

  • Trisomy – additional Chromosome to the pair eg trisomy 21

  • Monosomy – only one chromosome, one missing from the pair (lethal)

  • named for the Chromosome # involved

  • Karyotype is the characteristic chromosome complement of a eukaryote species


  1. Trisomy 21

  2. Turners Syndrome

  • female XO (1 in 3000 live births)

  1. Klinfelters syndrome

  • male XXY (1 in 500)

  • fig 7-11


Structural defects:

  1. Chromosomal deletion: The loss of a segment of the genetic material from a chromosome.


  1. Chromosomal Inversion: a chromosome rearrangement in which a segment of a chromosome is reversed end to end.

  2. Chromosome translocation: is a chromosome abnormalitycaused by rearrangement of parts between nonhomologous chromosomes.

Martin, Glenn and Porth, Carol, Mattson. 2009. Pathophysiology Concepts of Altered Health States. 8th ed. Lippincott Williams and Wilkins. Philadelphia

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