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2020 January 20
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The suggestion that malocclusion has a genetic component comes from observations of mandibular prognathism (frequently associated with Angle’s Class III) segregating in families. Probably the best-known example is the House of Habsburg, which produced emperors and kings of Bohemia (current Czech Republic), England, Germany, Hungary, Croatia, Illyria (a region of Austria), the Mexican second empire, Ireland, Portugal, Spain, and several administrators and principalities of Denmark and Italy (Fig 1).3 Since many cases of mandibular prognathism aggregate in families, there is the perception that it follows an autosomal dominant Mendelian mode of inheritance (monogenic or single gene). The perception that one gene with a main effect leads to mandibular prognathism4 motivated linkage5-8 and association9-17 studies under the hypothesis that a strong genetic effect can be identified even with relatively small sample sizes (definitions of linkage and association studies are provided at the end of this article). These results are inconsistent, suggesting that monogenic inheritance and a gene with a major effect are not the best explanation for the majority of cases of malocclusion. Currently, it is understood that inheritance of mandibular prognathism and malocclusions in general is multifactorial or complex, which means that more than one gene (instead of just one) contribute to the establishment of malocclusion, and these genes can be influenced by the environment. Like for other conditions, there are exceptions, and a major gene effect with autosomal dominant inheritance may be possible.