Enzyme deficiencies and iodine intake can interact to determine goitre formation in non-endemic areas.
Underlying predisposition
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Enzyme deficiencies of varying severity may explain many sporadic goitres in non-endemic areas.
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A family history is often present and suggests a genetic defect.
Influence of iodine intake
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High iodine intake may compensate for the underlying predisposition. The passage illustrates this with Iceland, where an iodine-rich fish diet accompanies the near absence of goitre.
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Low iodine intake encourages goitre formation in people with a metabolic predisposition.