Investigation of molecular diagnosis by alkaline phosphatase gene sequence analysis in patients with low alkaline phosphatase levels and thought to be clinically hypophosphatasia

OBJECTIVE: In this study, we aimed to investigate the molecular diagnosis of patients with low alkaline phosphatase levels and who were thought to have hypophosphatasia clinically. MATERIAL AND METHODS: During a period from January 2104 to October 2018 at Ege University Hospital, patients with serum alkaline phosphatase levels less than 40 U / L and aged 0-20 years were recorded.. We searched all ALP values recorded in the electronic patient file of our hospital and hospital records. Patients who had normal and high ALP values with previous tests were excluded.When the records were evaluated, cases with a history of clinical situation and drug use, which could lead to decrease ALP levels other than hypophosphatasia, were excluded from the study list. Following this exclusion, 273 people were included in the study. The selected cases were evaluated for the second time. After this evaluation, 147 cases were excluded. The remaining 126 cases were called with the registered phone numbers in our hospital system. The causes of low ALP levels were explained in details and they were called for control examination. Thirty patients were included in the study. Detailed anamnesis of the cases, the family histories were noted, and we performed their physical examinations. The family tree was drawn. Serum ALP levels were re-studied, and serum calcium, phosphorus, urine calcium / creatinine levels were examined. For definite diagnosis of hypophosphatasia, we performed ALPL gene sequence analysis from the blood samples. RESULTS: The median age of the 30 patients included in the study was 20.35 (minimum: 6.1, maximum 22.5). In the study group, 3 patients were male and 27 were female. In five patients, heterozygous pathogenic mutations were detected in 4 cases and the single allele deletion was detected in one case. These mutations were the heterozygous missense c.657G>T (p.Met219Ile) mutation, heterozygous c.648 + 1G> A mutation, heterozygous missense c.542C> T (p.Ser181Leu) mutation, heterozygous c.862 + 1G> C mutation. The group with mutation / deletion group and the normal group analysis were compared with anamnesis, clinical features and laboratory findings. Control ALP levels and mean ALP levels were lower in the mutation / deletion group. Control ALP values were 30 U / L (minimum: 23U / L; maximum 45 U / L) in the mutation / deletion group, and 41U / L (minimum: 26U / L; maximum: 194U / L) in the group with normal sequence analysis. There was a significant difference between ALP levels of both groups (p: 0.036). When the ALP mean values of the vi cases were compared, the difference between the two groups was also significant (p: 0.028). The median value of ALP was 27 U / L (minimum 22.5 U / L; maximum: 39 U / L) in the mutation / deletion group and 37.6 U / L (minimum: 22.5 U / L; maximum: 113,5 U / L) in the other group. In one of the cases with pathogenic mutation detected according to ACMG 2015 criteria, we found right arm fracture due to trauma in infantile period. In our other case (case 2), the presence of chest deformity was prominent. In case 3, significant scoliosis was detected in childhood. In this patient, Z score was decreased in the bone densitometry. In case 5, there were seizures occurring in infantile period, which could be significant for hypophosphatasia and in the physical examination there were short stature, genu valgus, a significant decrease of bone density. In our case, we learned the history fracture due to trauma for 2 times in childhood. İn the physical examination we noted short stature. CONCLUSION: In our study, compared with normal sequence analysed group, mutation \ deletion detected group had lower ALP values. Compared to other studies ;our lower ALP limit value helped us to detect more cases with pathogenic changes in sequence analyse. Hypophosphatase may present a variety of clinical signs ranging from severe to mild. It should be kept in mind that hypophosphatasia may be present in cases with skeletal system findings (bone deformities, short stature, frequent fractures, etc.) and other symptoms as well as low ALP.