Dictionary of Medical Terms You'll See

Entering the world of genetics and disorders has opened a new vocabulary for us. Here are some of the key phrases we repeatedly encounter:

Autosomal dominant: means the presence of one abnormal gene from one parent is needed in order for the disorder to develop. The abnormal gene "dominates" the pair of genes even if the matching gene from the other parent is normal.

Variable expressivity : Variable expressivity refers to the degree to which a condition or disorder is expressed in an individual. It's like a dimmer switch on a light. If there's a mutation present, the switch is turned on but how much shows is controlled by the expressivity dimmer switch. It's because of this changing level of severity that gives us such a broad prevalence statistic. Some families don't know they have it until a child is born with more obvious characteristics or complications leading to difinitive diagnosis.

Phenotype/Genotype: One's phenotype is their physical appearance which is determined by their genotype - which genes are dominant. When discussing Noonan Syndrome, the phrase Phenotype-Genotype Correlation arrises. This refers to which physical characteristics are more prevalent with each known gene mutation. For example, hypertrophic cardiomyopathy (HCM)is most commonly associated with RAF1 mutations or "the phenotype of HCM is correlated to the RAF1 genotype".

Missense mutation: A single nucleotide (C, G, A, T) is changed resulting in the production of a different amino acid. This in turn affects the resulting protein which in turn can affect physical development, mental accuity, heart development, etc.

Germline mutation: The mutation happens within the germ cells - sperm or ova. By contrast, somatic mutations happen in mature cells such as in the development of cancer.

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