University of Southern Denmark Multiple Fractures and Impaired Bone Fracture Healing in a Patient with Pycnodysostosis and Hypophosphatasia Hepp, Nicola; Frederiksen, Anja Lisbeth; Dunø, Morten; Jørgensen, Niklas Rye; Langdahl, Bente; Vedtofte, Poul; Hove, Hanne B.; Hindsø, Klaus; Jensen, Jens Erik Beck Published in: Calcified Tissue International DOI: 10.1007/s00223-019-00605-1 Publication date: 2019 Document version: Accepted manuscript Citation for pulished version (APA): Hepp, N., Frederiksen, A. L., Dunø, M., Jørgensen, N. R., Langdahl, B., Vedtofte, P., Hove, H. B., Hindsø, K., & Jensen, J. E. B. (2019). Multiple Fractures and Impaired Bone Fracture Healing in a Patient with Pycnodysostosis and Hypophosphatasia. Calcified Tissue International, 105(6), 681-686. https://doi.org/10.1007/s00223-019-00605-1 Go to publication entry in University of Southern Denmark's Research Portal Terms of use This work is brought to you by the University of Southern Denmark. Unless otherwise specified it has been shared according to the terms for self-archiving. If no other license is stated, these terms apply: • You may download this work for personal use only. • You may not further distribute the material or use it for any profit-making activity or commercial gain • You may freely distribute the URL identifying this open access version If you believe that this document breaches copyright please contact us providing details and we will investigate your claim. Please direct all enquiries to [email protected] Download date: 29. Sep. 2021 Multiple fractures and impaired bone fracture healing in a patient with pycnodysostosis and hypophosphatasia Nicola Hepp1, Anja Lisbeth Frederiksen2,3, Morten Dunø4, Niklas Rye Jørgensen5,6, Bente Langdahl7, Poul Vedtofte8, Hanne B. Hove9, Klaus Hindsø10 and Jens-Erik Beck Jensen1,11 1 Dept. of Endocrinology, Hvidovre University Hospital Copenhagen, Kettegård Alle 30, 2650 Hvidovre, Denmark 2 Dept. of Clinical Genetics, Odense University Hospital, Winsløws Vej 4, 5000 Odense C, Denmark 3 Department of Clinical Research, Faculty of Health, University of Southern Denmark, Winsløwparken 19. 3, 5000 Odense C, Denmark 4 Dept. of Clinical Genetics, University Hospital Copenhagen Rigshospitalet, Blegdamsvej 9, 2100 Copenhagen, Denmark 5 Dept. of Clinical Biochemistry, Rigshospitalet, Valdemar Hansens Vej 13, 2600 Glostrup, Denmark 6 OPEN, Odense Patient data Explorative Network, Odense University Hospital/Institute of Clinical Research, University of Southern Denmark, J.B.Winsløws Vej 9, 5000 Odense C, Denmark 7 Dept. of Endocrinology and Internal Medicine, Aarhus University Hospital, Palle Juul Jensens Boulevard 99, G317, 8200, Aarhus N, Denmark 8 Dept. of Oral and Maxillofacial Surgery, University Hospital Copenhagen Rigshospitalet, Blegdamsvej 9, 2100 Copenhagen, Denmark Abbreviations: ALP, alkaline phosphatase; ALPL, TNSALP encoding gene; BALP, bone specific alkaline phosphatase; BMC, bone mineral content; BMD, bone mass density; CPAP, continuous positive airway pressure; CT, computed tomography; CTSK, cathepsin K; CTSK, cathepsin K encoding gene; CTX, c-terminal telopeptide of type I collagen; DXA, dual energy X-ray absorptiometry; ECM, bones extracellular matrix; FGF23, fibroblast growth factor 23; HPP, hypophosphatasia; HR- pQCT, high-resolution peripheral quantitative computed tomography; nr, normal range; OB, osteoblasts; OC, osteoclasts; PEA, phosphoethanolamine; Pi, inorganic phosphate; PINP, plasma procollagen type 1 N-terminal propeptide; PLP, pyridoxal-5´-phosphate; PPi, inorganic pyrophosphate; PTH, parathyroid hormone; rd, reference data; TBS, trabecular bone score; TNSALP, tissue-non- specific alkaline phosphatase; TRAP-5b, tartrate-resistant acid phosphatase-5b; vBMD, volumetric bone mineral density 1 9 Center for Rare Diseases, Dept. of Pediatrics, University Hospital Copenhagen, Juliane Maries Vej 6, 2100 Copenhagen, Denmark 10 Paediatric section, Dept. of Orthopedic Surgery, University Hospital Copenhagen Rigshospitalet, Blegdamsvej 9, 2100 Copenhagen, Denmark 11 Dept. of Clinical Medicine, University of Copenhagen, Blegdamsvej 9, 2100 Copenhagen, Denmark Corresponding Author: Nicola Hepp, MD, PhD-student Dept. of Endocrinology, Hvidovre University Hospital Kettegård Alle 30 2650 Hvidovre Denmark Phone: +4553625083 [email protected] Anja Lisbeth Frederiksen (ALF): [email protected] Morten Dunø (MD): [email protected] Niklas Rye Jørgensen (NRJ): [email protected] Bente Langdahl (BL): [email protected] Poul Vedtofte (PV): [email protected] Hanne B. Hove (HBH): [email protected] Klaus Hindsø (KH): [email protected] Jens-Erik Beck Jensen (JEBJ): [email protected] 2 Abstract Pycnodysostosis (PYCD) is a rare recessive inherited skeletal disease, characterized by short stature, brittle bones and recurrent fractures, caused by variants in the Cathepsin K encoding gene (CTSK) that leads to impaired osteoclast mediated bone resorption. Hypophosphatasia (HPP) is a dominant or recessive inherited condition representing a heterogeneous phenotype with dental symptoms, recurrent fractures and musculoskeletal problems. The disease results from mutation(s) in the tissue-nonspecific alkaline phosphate (TNSALP) encoding gene (ALPL) with reduced activity of alkaline phosphatase (ALP) and secondarily defective mineralization of bone and teeth. Here, we present the first report of a patient with the co-existence of PYCD and HPP. This patient presented typical clinical findings of PYCD, including short stature, maxillary hypoplasia and sleep apnoea. However, the burden of disease was caused by over 30 fractures, whereupon most showed delayed healing and non-union. Biochemical analysis revealed supressed bone resorption and low bone formation capacity. We suggest that the co-existence of impaired bone resorption and mineralization may explain the severe bone phenotype with poor fracture healing. Keywords Pycnodysostosis; hypophosphatasia; CTSK; fracture; bone healing 3 Introduction Pycnodysostosis (PYCD) is an inborn recessive skeletal dysplasia with a prevalence of 1-1.7 per million [1, 2]. The disease is caused by Cathepsin K (CTSK) deficiency encoded by CTSK [3]. The protease CTSK is essential for the bone-resorbing osteoclasts (OC) to degrade bone matrix proteins, and impairment leads to failure of bone resorption and remodelling [4-7]. The clinical presentation is characterized by brittle bones, small stature, craniofacial and oral abnormalities, including micrognathia and dental crowding [8, 9]. The tissue-non-specific alkaline phosphatase (TNSALP) is an important enzyme for normal skeletal and dental mineralization [10]. Here, deficiency caused by mutation(s) in the TNSALP encoding gene (ALPL) leads to the rare bone disease Hypophosphatasia (HPP) [11]. Clinical manifestations of HPP in adults are highly variable, including stress and fragility fractures, dental symptoms, muscle weakness, chronic pain in the lower extremities and kidney stones [12-14]. Persistently low levels of the TNSALP and an elevation of its substrates pyridoxal-5´-phosphate (PLP) and phosphoethanolamine (PEA) are biochemical hallmarks [15]. We report a 29-year old woman clinically diagnosed with PYCD in early childhood who has encountered over 30 fractures with delayed healing and most resulted in non-union. At the age of 25 years, we observed persistently low levels of alkaline phosphatase (ALP), an uncommon biochemical finding of PYCD [2, 4, 8, 16-18]. Genetic analysis identified the co- existence of a novel presumed pathogenic heterozygous variant in ALPL. Here, we describe clinical, genetic, biochemical findings as well as results of dual energy X-ray absorptiometry (DXA) and high-resolution peripheral quantitative computed tomography (HR-pQCT). 4 Material and Methods A detailed description of the material and methods is attached in the supplementary material. Results Clinical, genetic, and biochemical findings of the studied family The patient, a Caucasian woman, was born as the first child to non-consanguineous parents at term after an uneventful pregnancy with a birth weight of 2900 g and a length of 50 cm. At the age of 18 months, she was clinically diagnosed with PYCD. From age 4 until 14 years, the patient underwent growth hormone therapy. At the age of 12, sleep apnoea was diagnosed due to a restricted upper airway, midface retrusion and a long soft palate and treated with continuous positive airway pressure (CPAP). Additional co-morbidities include generalised epilepsy of unknown origin, diagnosed at the age of 17 years and migraine without aura. Further, the patient receives Levothyroxine due to mild non-autoimmune hypothyroidism. Genetic analyses of the patient revealed compound heterozygous variants in CTSK, c.121- 1G>A; c.926C>T, p.Leu309Pro respectively. The parents were heterozygote carriers and both variants were previously reported in Danish patients with PYCD [19]. Subsequent sequencing of ALPL identified a novel heterozygous variant in exon 12 (c.1487A>G, p.His496Arg) both in the patient and her father. The variant is not reported in the gnomAD database, which describes more than 265.000 alleles in the area, nor in the ALPL mutation database (http://www.sesep.uvsq.fr/ 03_hypo_mutations.php). In silico analysis predicts the variant to have pathogenic potential. The patient’s mother has never experienced fractures, or dental problems. Opposite, the father presented several dental symptoms, including severe caries and enamel-defects