Combination of osteogenesis imperfecta and hypophosphatasia in three children with multiple fractures, low bone mass and severe osteomalacia, a challenge for therapeutic management

Nadja Fratzl-Zelman; Agnès Linglart; Kim Bin; Frank Rauch; Stéphane Blouin; Régis Coutant; Aurélie Donzeau

doi:10.1016/j.ejmg.2023.104856

Combination of osteogenesis imperfecta and hypophosphatasia in three children with multiple fractures, low bone mass and severe osteomalacia, a challenge for therapeutic management

Eur J Med Genet. 2023 Nov;66(11):104856. doi: 10.1016/j.ejmg.2023.104856. Epub 2023 Sep 25.

Authors

Nadja Fratzl-Zelman¹, Agnès Linglart², Kim Bin³, Frank Rauch⁴, Stéphane Blouin⁵, Régis Coutant⁶, Aurélie Donzeau⁷

Affiliations

¹ Ludwig Boltzmann Institute of Osteology at Hanusch Hospital of OEGK and AUVA Trauma Centre Meidling, 1st Med. Department Hanusch Hospital, Vienna, Austria; Vienna Bone and Growth Center, Vienna, Austria. Electronic address: nadja.fratzl-zelman@osteologie.lbg.ac.at.
² AP-HP, Paris Saclay University, INSERM, Reference Center for Rare Diseases of the Calcium and Phosphate Metabolism, Platform of Expertise for Rare Diseases, OSCAR Filière, EndoERN and BOND ERN Center, Endocrinology and Diabetes for Children, Bicêtre Paris Saclay Hospital, France.
³ Pediatric Orthopedic Surgery Angers University Hospital, Angers, France.
⁴ Shriners Hospital for Children, Canada, Montreal, QC, Canada.
⁵ Ludwig Boltzmann Institute of Osteology at Hanusch Hospital of OEGK and AUVA Trauma Centre Meidling, 1st Med. Department Hanusch Hospital, Vienna, Austria; Vienna Bone and Growth Center, Vienna, Austria.
⁶ AP-HP, Paris Saclay University, INSERM, Reference Center for Rare Diseases of the Calcium and Phosphate Metabolism, Platform of Expertise for Rare Diseases, OSCAR Filière, EndoERN and BOND ERN Center, Endocrinology and Diabetes for Children, Bicêtre Paris Saclay Hospital, France; Department of Pediatric Endocrinology and Diabetology, Competence Center for Rare Diseases of the Calcium and Phosphate Metabolism, Angers University Hospital, Angers, France.
⁷ Department of Pediatric Endocrinology and Diabetology, Competence Center for Rare Diseases of the Calcium and Phosphate Metabolism, Angers University Hospital, Angers, France.

PMID: 37758163
DOI: 10.1016/j.ejmg.2023.104856

Abstract

Osteogenesis imperfecta (OI) and hypophosphatasia (HPP) are rare skeletal disorders caused by mutations in the genes encoding collagen type I (COL1A, COL1A2) and tissue-non-specific isoenzyme of alkaline phosphatase (ALPL), respectively. Both conditions result in skeletal deformities and bone fragility although bone tissue abnormalities differ considerably. Children with OI have low bone mass and hypermineralized matrix, whereas HPP children develop rickets and osteomalacia. We report a family, father and three children, affected with growth retardation, low bone mass and recurrent fractures. None of them had rickets, blue sclera or dentinogenesis imperfecta. ALP serum levels were low and genetics revealed in the four probands heterozygous pathogenic mutations in COL1A2 c.838G > A (p.Gly280Ser) and in ALPL c.1333T > C (p.Ser445Pro). After multidisciplinary meeting, a diagnostic transiliac bone biopsy was indicated for each sibling for therapeutic decision. Bone histology and histomorphometry, as compared to reference values of children with OI type I as well as, to a control pediatric patient harboring the same COL1A2 mutation, revealed similarly decreased trabecular bone volume, increased osteocyte lacunae, but additionally severe osteomalacia. Quantitative backscattered electron imaging demonstrated that bone matrix mineralization was not as decreased as expected for osteomalacia. In summary, we observed within each biopsy samples classical features of OI and classical features of HPP. The apparent nearly normal bone mineralization density distribution results presumably from divergent effects of OI and HPP on matrix mineralization. A combination therapy was initiated with ALP enzyme-replacement and one month later with bisphosphonates. The ongoing treatment led to improved skeletal growth, increased BMD and markedly reduced fracture incidence.

Keywords: Bone biopsy samples; Bone histomorphometry; Mineralization; Quantitative backscattered electron microscopy; Rare bone disorders; Therapy.

MeSH terms

Alkaline Phosphatase / genetics
Calcinosis*
Child
Fractures, Multiple*
Humans
Hypophosphatasia* / drug therapy
Hypophosphatasia* / genetics
Mutation
Osteogenesis Imperfecta* / drug therapy
Osteogenesis Imperfecta* / genetics
Osteomalacia* / genetics
Osteomalacia* / pathology
Rickets*

Substances

Collagen Type I, alpha2 Subunit
Alkaline Phosphatase