Different Dental Manifestations in Sisters with the Same ALPL Gene Mutation: A Report of Two Cases

Hypoalkaline Phosphatemia Dental Type: A Case Report

Mutations in dental hypophosphatasia (HPP) have been reported less than those in other types of HPP because the symptoms are mild or the dental lesions are only partial manifestations of other types of HPP. In this case, we observe the clinical manifestation of dental hypoalkaline phosphatase by analyzing the genetic mutation and biochemical parameters in child. The clinical data of the child with odonto HPP were collected and analyzed. The blood samples of the child and his parents were sequenced and verified using Sanger through a specific probe capture and high-throughput second-generation sequencing technology. Major clinical manifestations in the patient were early loss of deciduous teeth, significantly lower serum alkaline phosphatase (ALP) levels, lower active vitamin D, and increased blood phosphorus, but no abnormality was observed in the oral X-ray. Two missense mutations-c.542C>T (p. ser181leu) and c.644 T> C (p.Ile215Thr)-were found in exon 6 of the ALPL gene from the father and mother, respectively. The clinical manifestations of odonto hypophosphatasia were early loss of deciduous teeth and significantly reduced serum ALP levels. Of 2 mutations-c.542C>T (p.ser181leu) and c.644 T> C (p.Ile215Thr)-in the ALPL gene, c.644 T> C (p.Ile215Thr) was a new mutation.

A case report of odonto-hypophosphatasia with a novel variant in the ALPL gene

OBJECTIVES

Hypophosphatasia (HPP) is a rare skeletal dysplasia caused by variants in the alkaline phosphatase (ALPL) gene. More than 400 pathogenic variants of the ALPL gene have been registered in the ALPL gene variant database. Here, we describe the case of a Japanese child with odonto-hypophsphatasia (odonto-HPP) and a novel ALPL variant.

CASE PRESENTATION

At the age of 2 years and 1 month, he prematurely lost one deciduous tooth, with the root intact, when he fell and hit his face lightly. Three months later, he lost another adjacent deciduous tooth without incentive. His serum alkaline phosphatase (ALP) level was 72 U/L. His urine phosphoethanolamine (PEA) level was extremely high at 938 μmol/mg·Cre. The serum pyridoxal 5'-phosphaye (PLP) level was 255.9 nmol/L. Based on the clinical symptoms and laboratory findings, the patient was clinically diagnosed with odonto-HPP. Genetic analysis of the ALPL gene revealed a heterozygous variant (NM_000478.6:c.1151C>A, p.Thr384Lys).

CONCLUSIONS

We report a case of odonto-HPP with a novel variant in the ALPL gene. HPP is a rare disease, and the heterozygous mutation in the ALPL gene highlights the novelty of this case.