Molecular diagnosis of hypophosphatasia and differential diagnosis by targeted Next Generation Sequencing

Abstract

Hypophosphatasia (HPP) is a rare inherited skeletal dysplasia due to loss of function mutations in the ALPL gene. The disease is subject to an extremely high clinical heterogeneity ranging from a perinatal lethal form to odontohypophosphatasia affecting only teeth. Up to now genetic diagnosis of HPP is performed by sequencing the ALPL gene by Sanger methodology. Osteogenesis imperfecta (OI) and campomelic dysplasia (CD) are the main differential diagnoses of severe HPP, so that in case of negative result for ALPL mutations, OI and CD genes had often to be analyzed, lengthening the time before diagnosis. We report here our 18-month experience in testing 46 patients for HPP and differential diagnosis by targeted NGS and show that this strategy is efficient and useful. We used an array including ALPL gene, genes of differential diagnosis COL1A1 and COL1A2 that represent 90% of OI cases, SOX9, responsible for CD, and 8 potentially modifier genes of HPP. Seventeen patients were found to carry a mutation in one of these genes. Among them, only 10 out of 15 cases referred for HPP carried a mutation in ALPL and 5 carried a mutation in COL1A1 or COL1A2. Interestingly, three of these patients were adults with fractures and/or low BMD. Our results indicate that HPP and OI may be easily misdiagnosed in the prenatal stage but also in adults with mild symptoms for these diseases.

Safety and efficacy of treatment with asfotase alfa in patients with hypophosphatasia: Results from a Japanese clinical trial

“…Thus, the early diagnosis of HPP is important in this situation. A treatment algorithm for HPP has been proposed . Other therapies including teriparatide, bone marrow transplantation and gene induction have been reported .…”

Osteomalacia with low alkaline phosphatase: a not so rare condition with important consequences

“…This is the reason why pyridoxine-responsive seizures are an indication of the severity of the disease and the possible lethal prognosis 7. The clinical expression varies from a total lack of bone mineralisation, which leads to stillbirth, to stress fractures and premature deciduous or permanent teeth loss in adults, as was the case in our patient 8. A description of the clinical presentation of each form of HPP is given in table 1.…”

Differential diagnosis of perinatal hypophosphatasia: radiologic perspectives

“…Genetic testing for ALPL mutations can be confirmatory in cases of diagnostic uncertainty [91, 92]. However, clinicians should be aware of the depth of coverage with whole-exome sequencing and next-generation sequencing technology, as some pathogenic variants may not be detected [92, 93].…”