Circulating miRNAs and Bone Microstructure in Adults With Hypophosphatasia
Circulating miRNAs and Bone Microstructure in Adults With Hypophosphatasia
The aim of the study is to accomplish a complete bone status of patients with HPP using new
 approaches to assess bone quality.
Hypophosphatasia (HPP) is a hereditary disease of bone metabolism that is not yet curable.
 Clinical phenotype is variable and reaches from demineralization of bone, deformation of the
 skeleton, microsomia and gait abnormality to breathing difficulties. Symptoms of the adult
 form are low-traumatic fractures, hip or thigh pain and arthropathy. Cause of the disease is
 a mutation in the ALPL-gene (1p36.1-p34) coding for the tissue-nonspecific isoenzyme of
 alkaline phosphatase (TNAP) in liver, bone and kidney. This leads to a low activity of
 alkaline phosphatase (AP) and elevated levels of phosphoethanolamine (PEA) in urine.

 HPP is a very rare disease with a prevalence of ~1/100 000. The Medical Department II of the
 St. Vincent Hospital Vienna, Department of the Medical University of Vienna and the Sigmund
 Freud University Vienna is a department that is specialized on bone diseases and, as a member
 of "Orphanet", also on In particular, (i) bone microstructure as a main component of bone
 strength and (ii) circulating microRNAs (miRNAs) as promising biomarkers for bone diseases
 will be analyzed in patients with HPP and age-, and gender-matched healthy controls.

 Microstructural deteriorations of cortical and trabecular bone as well as volumetric bone
 density (vBMD) in radius and tibia in patients with HPP will be compared to healthy
 individuals using HR-pQCT (High resolution peripheral quantitative computer tomography,
 Scanco Medical, Brütisellen). HR-pQCT is a high-resolution, non-invasive technique to measure
 cortical and trabecular bone mircostructures as well as vBMD at a high resolution level
 (82µm).

 Micro-RNAs (miRNAs) are short, non-coding RNA molecules of which some have been identified as
 bone specific (e.g. miR-31, miR-335, miR-155, miR-29b, miR-188, miR-550a). They play a
 significant role in bone metabolism controlling synthesis and function of osteoblasts as well
 as osteoclasts.

 In recent studies we could show that these microRNAs can be detected in serum and that their
 serum concentration correlates with the risk for osteoporotic fractures. Data for patients
 with HPP do not exist yet. miRNAs will be measured by qPCR (quantitative polymerase chain
 reaction) in serum of patients with HPP and respective controls.

 In addition, measurements of areal BMD (aBMD) by DXA (Dual Energy X-ray Absorptiometry) and
 DXL (Dual X-ray and Laser) will be performed. Vitamin D and established bone turnover markers
 including PINP (N-terminal propeptide of type I collagen), CTX (collagen type 1 cross-linked
 C-telopeptid) and sclerostin will be analyzed. Moreover, body composition will be determined.
Inclusion Criteria for Hypophosphatasia (HPP)

 -  genetically verified hypophosphatasia

 -  age >18 years

 -  written informed consent

 -  complete serological and radiological examinations

 Inclusion Criteria für Controls:

 -  healthy men and women without any history of musculoskeletal diseases

 -  written informed consent

 -  Alkaline phosphatase (AP) in reference range

 -  complete serological and radiological examinations

 Exclusion Criteria for both Groups:

 -  inflammatory diseases

 -  other genetic disorders affecting bone such as osteogenesis imperfecta,
 Ehlers-Danlos-syndrome and fibrous dysplasia

 -  diabetes mellitus type 1 and 2

 -  COPD

 -  chronic kidney and liver dysfunction

 -  systemic glucocorticoid use and glucocorticoid induced osteoporosis

 -  eating disorders

 -  HIV-infections and any malignancy including plasmacytosis and lymphoma.