Résumé
Objective:Clinical and genetic analysis were conducted in 2 patients with hypophosphatasia(HPP) and their families to explore the pathogenic mechanism of HPP.Methods:The genomic DNA was extracted from peripheral blood of two patients with HPP and their family members. Sanger sequencing and pedigree verification were performed on the pathogenic variants identified using whole-exome sequencing. Then the function of the mutation sites was analyzed with bioinformatics software.Results:Proband 1 presented with developmental retardation, pectus funnel and premature loss of deciduous tooth, of which the serum alkaline phosphatase level was slightly lower than the bound of the normal range. Two complex heterozygous missense variants c. 1120G>A and c. 1334C>G of ALPL gene were detected in the proband 1 which were inherited from his parents respectively, showing an autosomal recessive inheritance. Both the variants were predicted to inflict deleterious effects on ALPL gene function by multiple bioinformatics program, and were classified as likely pathogenetic variants according to American College of Medical Genetics and Genomics(ACMG) guidelines. Proband 2 showed three missing permanent teeth and the significantly lower level of serum alkaline phosphatase than normal range. A heterozygous variant c. 1190-3C>G of ALPL gene was detected in proband 2 whose pattern of inheritance was unknown. The clinical significance of this variant was unknown according to ACMG standards and guidelines. All of these variants were considered as novel since none of them has been reported. Along with the above combined results, proband 1 and 2 were diagnosed as childhood HPP and Odontohypophosphatasia, respectively.Conclusion:This study reinforced the relationship between HPP and variants in ALPL gene. Two variants, c. 1120G>A and c. 1334C>G, were located in the homodimer interface and crown domain of tissue-nonspecific alkaline phosphatase(TNSALP), respectively, while c. 1190-3C>G were located in the splice sites, which might result in low TNSALP activity.
Résumé
Objective To investigate the role of TNSALP gene detection in prenatal diagnosis of HPP. Method The clinical data and the results of complete exon sequencing of TNSALP gene in one neonate with low alkaline phosphatase (HPP) were analyzed retrospectively. Peripheral bloods from his family members were collected. The amniotic fluid cell in fetuses at 17 weeks was tested for candidate gene mutations by Sanger sequencing. Results Mainly manifestations in 6-day-old baby were multiple fractures, limb shortening and bending and dyspnea. He died of respiratory failure 9 days after birth. The serum alkaline phosphatase was decreased and serum calcium was decreased slightly; serum phosphorus, serum 25 hydroxyvitamin-D and parathyroid hormone were normal. X-ray showed that the whole body bone was very poorly mineralized, and the long diaphysis was enlarged with shape of a cup at the end and multiple fractures existed. Gene sequencing revealed a complex heterozygous missense mutation in the TNSALP gene, including the heterozygous missense mutation c.542C>T in exon sixth causing 181st amino acids changed from serine to leucine (p.S181L), and tenth exon heterozygous missense mutation in c.1016G>A causing 339th amino acid changed from glycine to glutamic acid (p.G339E). The parental phenotypes were normal. The c.542C>T mutation is inherited from his father and the c.1016G>A mutation is inherited from his mother. These two mutations were not detected in the fetus. Conclusion TNSALP gene analysis can be applied to the diagnosis and prenatal diagnosis of HPP.