Infantile hypophosphatasia due to a new compound heterozygous TNSALP mutation - functional evidence for a hydrophobic side-chain?

Utsch, B; Brun-Heath, I; Staatz, G; Gravou-Apostolatou, C; Karle, S; Jacobs, U; Ludwig, M; Zenker, M; Dörr, H-G; Rascher, W; Mornet, E; Dötsch, J (2009). Infantile hypophosphatasia due to a new compound heterozygous TNSALP mutation - functional evidence for a hydrophobic side-chain? Experimental and clinical endocrinology & diabetes, 117(1), pp. 28-33. Stuttgart: Thieme 10.1055/s-2008-1073157

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BACKGROUND: Infantile hypophosphatasia (IH) is an inherited disorder characterized by defective bone mineralization and a deficiency of alkaline phosphatase activity. OBJECTIVE/DESIGN: The aim of the study was to evaluate a new compound heterozygous TNSALP mutation for its residual enzyme activity and localization of the comprised amino acid residues in a 3D-modeling. PATIENT: We report on a 4-week old girl with craniotabes, severe defects of ossification, and failure to thrive. Typical clinical features as low serum alkaline phosphatase, high serum calcium concentration, increased urinary calcium excretion, and nephrocalcinosis were observed. Vitamin D was withdrawn and the patient was started on calcitonin and hydrochlorothiazide. Nonetheless, the girl died at the age of 5 months from respiratory failure. RESULTS: Sequence analysis of the patient's TNSALP gene revealed two heterozygous mutations [c.653T>C (I201T), c.1171C>T (R374C)]. Transfection studies of the unique I201T variant in COS-7 cells yielded a mutant TNSALP protein with only a residual enzyme activity (3.7%) compared with wild-type, whereas the R374C variant was previously shown to reduce normal activity to 10.3%. 3D-modeling of the mutated enzyme showed that I201T resides in a region that does not belong to any known functional site. CONCLUSION: We note that I201, which has been conserved during evolution, is buried in a hydrophobic pocket and, therefore, the I>T-change should affect its functional properties. Residue R374C is located in the interface between monomers and it has been previously suggested that this mutation affects dimerization. These findings explain the patient's clinical picture and severe course.

Item Type:	Journal Article (Further Contribution)
Division/Institute:	04 Faculty of Medicine > Department of Gynaecology, Paediatrics and Endocrinology (DFKE) > Clinic of Paediatric Medicine
UniBE Contributor:	Utsch, Boris
ISSN:	0947-7349
ISBN:	18523927
Publisher:	Thieme
Language:	English
Submitter:	Anette van Dorland
Date Deposited:	04 Oct 2013 15:03
Last Modified:	05 Dec 2022 14:19
Publisher DOI:	10.1055/s-2008-1073157
PubMed ID:	18523927
Web of Science ID:	000263268400006
URI:	https://boris.unibe.ch/id/eprint/27250 (FactScience: 105160)