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Genetic disorders (Investigations (Microarrays Indication: chromosomal…

- - - - Non-penetrance
        Lack of disease phenotype in person with the genotype
        E.g. otosclerosis
      - De novo mutation
        Arises spontaneously in child without affected parents
        Due to mutation in gametes, parental mosaicism, or non-paternity
        E.g. acondroplasia
      - Varied expression
        Some affected have milder/more severe disease,
        due to presence of other genes or environmental effect
      - Homozygosity
        Homozygous for AD often a more severe/lethal phenotype
      - Knudson's two hit hypothesis
        Inherited predisposition requiring a further somatic mutation to develop the phenotype e.g. Rb
    - - Consanguinty
        Shared genetic profile so increased
        risk of offspring having AR disorder
    - - Recessive
        Males affected
        Female carriers usually healthy
        e.g. colour blindness, DMD/BMD, Fragile X,
        Haemophilia A/B, Hunter syndrome, G6PD deficiency
        Important to identify carrier females
      - Dominant
        Rare
        Both males and females affected
        Disease usually more severe in males
        E.g. Rett syndrome - lethal during neonatal life in males, progressive neurodegeneration in female children