In DI, both the deciduous and permanent teeth are clinically affected, appearing blue-gray or amber brown and opalescent, although the deciduous teeth are often more severely affected. Radiographically, bulbous crowns, narrow roots, and small or obliterated pulp chambers and root canals are seen. Histologically, the dentin has a dys-plastic appearance with irregular dentinal tubules and areas lacking dentin tubules. Because of the defect in dentin, enamel is easily broken off, exposing the underlying dentin, leading to accelerated attrition. Three subtypes of DI have been recognized (table 1; fig. 1).
Individuals with DI type I have a syndromic form of DI. In addition to having DI, they also have osteogenesis imperfecta (OI), an autosomal dominant disorder of bone fragility. OI is further classified into collagenous and non-collagenous forms. All four collagenous OI subtypes can have DI as a feature. DI is more common in types III and IV. DI only occurs in cases of OI due to dominant negative effects (such as missense mutations). In some cases, DI may be the most penetrant clinical finding [Pallos et al., 2001]. Thus, it is important for health care providers to ask about histories of bone fractures (especially
Fig. 1. Clinical and radiographic features of DI types I—111 (a-g) and DD types I and II (h-j). a-c Individuals with DI type I. In this family, affected members also had OI type I due to a missense alteration in COL1A1 (p.Gly559Cys). a, b The constriction of the crown in the cervical region and almost complete obliteration of the pulp chambers. c The enamel has fractured from the central
Fig. 1. Clinical and radiographic features of DI types I—111 (a-g) and DD types I and II (h-j). a-c Individuals with DI type I. In this family, affected members also had OI type I due to a missense alteration in COL1A1 (p.Gly559Cys). a, b The constriction of the crown in the cervical region and almost complete obliteration of the pulp chambers. c The enamel has fractured from the central and lateral incisors, exposing the underlying yellow-brown dentin. d, e An individual with DI type II. f, g An affected male from the Brandywine cohort. h The extremely short roots characteristic of DD type I. i The phenotype in deciduous teeth that resembles DI type II, but the permanent teeth are normal in color. j The thistle-tube deformity commonly seen in DD type II.
with minimal trauma), joint hyperextensibility, short stature, hearing loss and scleral hue in all patients exhibiting DI. Approximately 90% of individuals with OI types I-IV have an identifiable mutation in COL1A1 or COL1A2, the two genes that encode the chains of type I procollagen [Steiner et al., 2005].
The presence of DI without other etiologically related clinical findings (i.e. non-syndromic DI) is classified as DI type II. The clinical and radiographic tooth phenotype is indistinguishable from that seen in syndromic DI type I. Penetrance is almost complete and de novo mutations are rare. The estimated incidence of DI type II is between 1/6,000 and 1/8,000 [Witkop, 1957]. A few families with DI type II have also had hearing loss, but it is not clear how the mutation in DSPP causes the hearing loss.
DI type III (OMIM 125500) was initially described in the Brandywine, triracial isolate in southern Maryland. The phenotype in this extended kindred can be traced to a sea captain from Liverpool who came to Maryland in 1732 [Witkop, 1965]. This isolate has the highest reported frequency of dental defects in the world, with approximately 6% having DI [Kim et al., 2005]. Overall, 1 in 15 individuals in this population is estimated to have DI [Witkop, 1957]. In addition to the abnormalities in tooth color and size seen in DI type II, very large pulp chambers and multiple pulp exposures are seen in deciduous teeth in approximately 2% of the Brandywine cohort. Enamel pitting has also been reported in some members of the Brandywine cohort [Levin et al., 1983]. These large pulp chambers led to the designation DI type III, however not all affected family members demonstrate large pulp chambers. Other unrelated families have been reported with these clinical features, demonstrating that the features associated with DI type III are not unique to the Brandywine cohort, and may represent variable clinical expression. Asymptomatic radiolucencies are sometimes seen in teeth with significant attrition. The Brandywine cohort also segregated juvenile periodontitis as an autosomal dominant trait [Boughman et al., 1986]. Linkage analysis supported the existence of a separate gene for juvenile periodontitis, located approximately 17 cM from the locus for DI type III.
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