Prognathism, Mandibular
Description
Mandibular prognathism is a dentofacial anomaly characterized by protrusion of the mandible, with lower incisors often overlapping the upper incisors. The protruding lower jaw is caused by a forward positioning of the mandible itself (summary by Stiles and Luke, 1953).
NomenclatureThe 'Habsburg Jaw' is an eponymous designation for patients with mandibular prognathism/hyperplasia since members of the ruling Habsburg (sometimes spelled 'Hapsburg') family, dominant in Europe between the 13th and 20th centuries, had seemingly large lower jaws. However, the facial abnormalities in this family may have been due to maxillary deficiency rather than mandibular prognathism (summary by Peacock et al., 2014; see HISTORY below).
Clinical FeaturesThompson and Winter (1988) described affected individuals in 3 generations. They pointed out that in addition to mandibular prognathism, there is thickened lower lip, flat malar areas, and mildly everted lower eyelids. One child in the family had craniosynostosis.
Chudley (1998) presented examples of the Habsburg jaw printed on postage stamps of Spain.
InheritanceMandibular prognathism was transmitted through many generations of the Hapsburg line as a dominant trait with incomplete penetrance (Rubbrecht, 1930; Strohmayer, 1937).
Stiles and Luke (1953) described a family in which members of 4 generations had mandibular prognathism. The pedigree pattern was consistent with autosomal dominant inheritance with incomplete penetrance.
Mandibular prognathism is a feature of the XXY, XXXY, and XXXXY syndromes and of interest is the progressive increase of this feature as the number of X chromosomes increases (Gorlin et al., 1965). Although the X chromosome has a role, the mendelian trait is not X-linked.
Wolff et al. (1993) assembled an extraordinary pedigree covering 23 generations and comprising 13 European noble families with mandibular prognathism. Pedigree analysis using the Elston-Stewart algorithm yielded a maximum likelihood estimate of penetrance of 95.5%.
Cruz et al. (2008) analyzed 55 Brazilian families with mandibular prognathism comprising 158 affected men and 214 affected women (male to female ratio of 1:1.35, p = 0.030). Inheritance was consistent with an autosomal dominant pattern in 89.1% of families. Thirty-two families had incomplete penetrance, and 17 showed complete penetrance. The incidence of mandibular prognathism was 14.3%, and heritability was estimated at 0.316. Cruz et al. (2008) concluded that there is a major gene that influences the expression of the trait with clear signs of mendelian inheritance.
HistoryThe prominent appearance of the jaw in members of the ruling Habsburg family in Europe, which has been documented in numerous portraits, has been attributed to mandibular prognathism. However, in a visual assessment of at least 3 portraits of 7 Spanish Habsburg emperors performed by 4 individuals specializing in oral and maxillofacial surgery, dentistry, and plastic and oral surgery, Peacock et al. (2014) concluded that the primary deformity in this family is maxillary deficiency resulting in midface hypoplasia rather than absolute mandibular prognathism. Eleven dysmorphic features for maxillary deficiency and 7 for mandibular prognathism were chosen and scored for diagnosis. The results also suggested that the Habsburg nasal deformity, characterized by a dorsal hump and overhanging nasal tip, and everted lower lip may both be explained by maxillary deficiency.