A Family Of Hypophosphatasia (HPP)

Objective To detect and analyze the Liver/Bone/Kidney Alkaline Phosphatase(ALPL)exons of a Chinese children with hypophosphatasia(HPP)and his family,at the same time,study on the pathogenic epitopes of the disease,investigate its pathogenic mechanism and the relationship between genotype and clinical phenotype.Methods 8 people enrolled in the study,including a 9 years old patient with HPP and his biological parents,grandparents,little brother,aunt,uncle.(1)The patient and his family were collected peripheral venous anticoagulant;(2)Genomic DNA from the peripheral venous blood was extracted using the Blood Genomic DNA Extraction Kit;(3)12 exons of Liver/Bone/Kidney Alkaline Phosphatase(ALPL)were amplified using PCR systems,and the DNA sequences were analyzed,then compared the sequence results with ALPL gene sequence(ID: 249)in Gene Bank.Results In the HPP family,the proband was the only patient,grandmother was the only normal family member,the other 6 family members were all carriers.The sequence analysis of ALPL exons revealed the existence of 4 points mutations in all,they were c.269A>G in exon 4(p.D90G),c.787T>C in exon 7(p.Y263H),c.330T>C in exon 5,and c.876A>G in exon 9 respectively.Among them,the former two points mutations were missense mutation,the later two were synonymous mutation.The substitution A?G at position 269-nt in exon 4 which leading to the substitution of glycine for asparagine 90 in ALPL polypeptide(p.D90G)was found in the proband and his grandfather,mother,uncle,but none of the later three had the skeletal and dental abnormalities,were all HPP carriers.The substitution T?C at position 787-nt in exon 7 which leading to the substitution of histidine for tyrosine 263 in ALPL polypeptide(p.Y263H)was found in the proband and his father,aunt,little brother,but none of the later three had the skeletal and dental abnormalities,were all HPP carriers.The homozygous synonymous mutation in exon 5 c.330T>C was found in the proband and his grandfather,grandmother,father,mother,aunt,uncle,little brother,serine was encoded before and after this mutation.The homozygous synonymous mutation in exon 9 c.876A>G was found in father and aunt,while heterozygous synonymous mutation in this site was found in the proband and his little brother,proline was encoded before and after this mutation.Conclusion c.269A>G in exon 4 in the proband was maternally inherited,and this mutation site in mother was paternally inherited.And c.787T>C in exon 7 in the proband was paternally inherited.Grandfather,mother and uncle only had a missense mutation(c.269A>G),while father,aunt and little brother only had a missense mutation(c.787T>C),none of these 6 people had the skeletal and dental abnormalities,were all HPP carriers.We can infer that c.269A>G may play a synergistic role with c.787T>C in the HPP onset of the family,so the proband was the only patient.The homozygous missense mutation in exon 7 c.787T>C was found in father and aunt,but they had no symptons,we guess functional domains of the protein which encoded by this site mutation was not affected.Further studies should be performed to confirm the above inferences.We can know that HPP' genotype and clinical phenotype were not consistent completely from the 6 carriers,and the detailed correlation between them need a large-scale trial to identify.