Five cases of hypophosphatasia with dental findings

Dental manifestation and management of hypophosphatasia

Hypophosphatasia is an inherited metabolic disorder characterized by defective mineralization of bones and teeth with a wide variety of manifestations, ranging from stillbirth to dental symptoms alone. Recently, the prognosis of severe hypophosphatasia patients has been greatly improved by the introduction of enzyme replacement therapy. The typical dental manifestation is early exfoliation of primary teeth due to disturbed cementum formation, so dentures are recommended to ensure that important oral functions are acquired. Some studies have shown that enzyme replacement therapy improves dental mineralization, resulting in the stabilization of periodontal tissues and better growth of tooth roots. A nationwide Japanese survey revealed the common genetic and dental manifestations of patients with mild hypophosphatasia, which markedly differ from those of the severe forms. There may be many undiagnosed mild patients, so dentists should contribute to the early diagnosis by screening possible cases based on the typical finding of early exfoliation of primary teeth. Early diagnosis is important for patients to receive early intervention in both medical and dental fields. The establishment of fundamental dental therapy to solve the dental problems is still underway and is eagerly anticipated.

Cementum and Dentin in Hypophosphatasia

Hypophosphatasia (HPP) often leads to premature loss of deciduous teeth, due to disturbed cementum formation. We addressed the question to what extent cementum and dentin are similarly affected. To this end, we compared teeth from children with HPP with those from matched controls and analyzed them microscopically and chemically. It was observed that both acellular and cellular cementum formation was affected. For dentin, however, no differences in mineral content were recorded. To explain the dissimilar effects on cementum and dentin in HPP, we assessed pyrophosphate (an inhibitor of mineralization) and the expression/activity of enzymes related to pyrophosphate metabolism in both the periodontal ligament and the pulp of normal teeth. Expression of nucleotide pyrophosphatase phosphodiesterase 1 (NPP1) in pulp proved to be significantly lower than in the periodontal ligament. Also, the activity of NPP1 was less in pulp, as was the concentration of pyrophosphate. Our findings suggest that mineralization of dentin is less likely to be under the influence of the inhibitory action of pyrophosphate than mineralization of cementum.

Enzyme replacement prevents enamel defects in hypophosphatasia mice

Hypophosphatasia (HPP) is the inborn error of metabolism characterized by deficiency of alkaline phosphatase activity, leading to rickets or osteomalacia and to dental defects. HPP occurs from loss-of-function mutations within the gene that encodes the tissue-nonspecific isozyme of alkaline phosphatase (TNAP). TNAP knockout (Alpl(-/-), aka Akp2(-/-)) mice closely phenocopy infantile HPP, including the rickets, vitamin B6-responsive seizures, improper dentin mineralization, and lack of acellular cementum. Here, we report that lack of TNAP in Alpl(-/-) mice also causes severe enamel defects, which are preventable by enzyme replacement with mineral-targeted TNAP (ENB-0040). Immunohistochemistry was used to map the spatiotemporal expression of TNAP in the tissues of the developing enamel organ of healthy mouse molars and incisors. We found strong, stage-specific expression of TNAP in ameloblasts. In the Alpl(-/-) mice, histological, µCT, and scanning electron microscopy analysis showed reduced mineralization and disrupted organization of the rods and inter-rod structures in enamel of both the molars and incisors. All of these abnormalities were prevented in mice receiving from birth daily subcutaneous injections of mineral-targeting, human TNAP at 8.2 mg/kg/day for up to 44 days. These data reveal an important role for TNAP in enamel mineralization and demonstrate the efficacy of mineral-targeted TNAP to prevent enamel defects in HPP.

Taurodontism in twins with cleft lip and/or palate

The aims of this study were to determine the frequency of taurodontism of the first and second permanent molars in twins discordant or concordant for clefts, the frequency for each type of cleft in twins, and the concordance-discordance ratio in mono- and dizygotic twins. Thirty-nine pairs of twins (13 monozygotic, 26 dizygotic) between the ages of 7 and 23 yrs were investigated. Taurodontism and hypodontia were determined from orthopantomograms of the dentition. Of the 39 pairs of twins investigated, 16 (41%) had taurodontism, equally in mono- and dizygotic pairs. The highest frequency of the trait was noted in subjects with isolated cleft palate and the lowest in cleft lip subjects. Four of 13 monozygotic pairs with taurodontism were concordant for the trait, as were 9 of 12 dizygotic pairs. Taurodontism was symmetric in 91% of the affected molar pairs. Concomitant taurodontism and hypodontia was observed in 8 of 16 taurodontic twin pairs. We conclude that the etiology of clefting in our group of twins seems to have an effect on the frequency of taurodontism. A high concordance for taurodontism and a high symmetry of the trait may indicate a strong genetic etiology of taurodontism.

Hypophosphatasia: dental aspects and mode of inheritance

Hypophosphatasia is rare enzymopathy that normally presents within the first few years of life and often has profound effects upon the periodontium. It is a heritable disorder characterised by defective mineralisation of the skeletal and dental structures of the body and a deficiency in the liver/bone/kidney (L/B/K) isoenzyme of alkaline phosphatase (ALP). There has been a tremendous advance in our knowledge of this condition over the last decade due to the advent of highly specific DNA probes and novel microanalytical techniques. This paper aims to review current literature about hypophosphatasia with special reference to the dental aspects of the condition and to shed light upon the controversial area of its mode of genetic inheritance. It is concluded that hypophosphatasia may result from the existence of 2 defective alleles, which alone or in combination may cause the condition. One allele is expressed in an autosomal dominant manner producing milder phenotypic characteristics, whilst the other is expressed in an autosomal recessive manner producing the more severe clinical form that often results in neonatal death. The milder phenotypes may go undiagnosed and the consequence of this in genetic counselling terms is extremely important.

Taurodontism in premolars

Taurodontism is not a dental anomaly that affects only the molars. In a review of 379 premolars extracted for different pathologic reasons, three cases of taurodontism were found. The three cases were in upper premolars and were studied anatomically and radiographically. The literature was reviewed, as well as the low incidence of the condition in premolars, which is probably related to a genetic condition. Our observations support this fact, as suggested by the study of our cases from a restricted population nucleus, within a district area of the city of Seville, Spain. Among the diagnostic criteria of taurodontism, those established by Shifman and Chanannel are more objective. Finally, our findings support an embryologic origin as a result of a delay in the apical epithelial diaphragm evagination or by interference in the epitheliomesenchymatose induction.

Hypophosphatasia: a family study involving a case diagnosed from gingival crevicular fluid

Hypophosphatasia is an inherited disorder characterized by defective mineralization of the skeletal and dental structures of the body and deficient liver/bone/kidney alkaline phosphatase (L/B/K ALP) activity. There has been a tremendous advance in our knowledge of this condition over the last decade due to the advent of highly specific DNA probes and novel microanalytic techniques. The purpose of this paper is threefold: to review the dental aspects of current literature about this rare condition; to present a case (and family study) that was diagnosed in a 5-yr-old boy from 0.14 microliters of gingival crevicular fluid, using a new ultrasensitive chemiluminescent assay for the enzyme alkaline phosphatase; and to provide strong evidence for an autosomal dominant mode of inheritance.

The incidence of taurodontism in dental patients

The incidence of taurodontism was investigated in a dental school patient population. Radiographic examinations of 1,581 patients were evaluated; of this population, 179 patients (11.3%) exhibited taurodontism. Thirty-eight patients had taurodonts as well as another dental anomaly of some type.