Skeletal consequences of familial hypocalciuric hypercalcaemia vs. primary hyperparathyroidism

Clinical Endocrinology (2009) 71, 798–807

doi: 10.1111/j.1365-2265.2009.03557.x

ORIGINAL ARTICLE

Skeletal consequences of familial hypocalciuric hypercalcaemia vs. primary hyperparathyroidism Signe Engkjær Christensen*, Peter H. Nissen†, Peter Vestergaard*, Lene Heickendorff†, Lars Rejnmark*, Kim Brixen‡ and Leif Mosekilde* *Department of Endocrinology and Metabolism C, †Department of Clinical Biochemistry, Aarhus University Hospital, Aarhus and ‡Department of Endocrinology, Odense University Hospital, Odense, Denmark

Summary Objectives Bone metabolism is only superficially described in familiar hypocalciuric hypercalcaemia (FHH). We describe and compare biochemical and osteodensitometric variables in FHH and primary hyperparathyroidism (PHPT) and assess whether they can improve the diagnostic discrimination between the groups. Design Cross-sectional. Patients Sixty-six FHH patients with known calcium-sensing receptor (CASR) gene mutations and 147 PHPT patients. Measurements We determined calcium, creatinine, phosphate, magnesium, parathyroid hormone (PTH), 25OHD, 1,25(OH)2D and alkaline phosphatase (AP) in plasma, NTx/creatinine ratio in urine and calculated the calcium/creatinine clearance ratio (CCCR). We performed dual energy X-ray absorptiometry at the lumbar spine, hip, forearm and whole body. Results When compared with normal controls, the FHH patients had increased levels of PTH and AP with normal U-NTx and regional Z-scores. Increased phenotypic expression of CASR mutations in terms of hypercalcaemia was associated with higher lumbar spine bone mineral density, but not with bone markers. FHH were younger and leaner than the PHPT patients. They had comparable plasma Ca2+ and 25OHD, but lower levels of PTH, 1,25(OH)2D, AP and U-NTx. They had higher Z-scores in the hip and in the forearm. We achieved the best discrimination between groups by multiplying CCCR with AP, 1,25(OH)2D and PTH, but the difference between the area under the curves by receiver operating characteristic analysis remained insignificant. Conclusion Familiar hypocalciuric hypercalcaemia is associated with increased PTH and AP compared to normal controls, but not with bone loss irrespective of the severity of the CASR mutations. A multiplicative model including CCCR, AP, 1,25(OH)2D and PTH insignificantly improved the power of the CCCR to differentiate between FHH and PHPT. However, we still recommend CASR gene analysis in patients with a CCCR 140 lmol/l), other calcium-metabolic or bone diseases, lithium treatment, systemic glucocorticoid treatment for more than 6 months, malignant disease, uncontrolled or newly diagnosed chronic disease, and hospital admission due to drug or alcohol abuse. As normal controls for vitamin D metabolites, we used data from 46 randomly selected healthy men and women matched by age (±5 years), sex and season (summer/winter).19–21 Other biochemical variables were compared with our normal laboratory reference values. The study was approved by the Regional Ethical Committee (Aarhus County #20030195). All patients with FHH gave informed verbal and written consent. The database was approved by the Danish Data Protection Agency. Methods Biochemistry. We measured plasma and urine calcium, plasma Ca2+, albumin, creatinine and phosphate by standard laboratory methods. We corrected total plasma calcium for individual variations in albumin.16  2009 Blackwell Publishing Ltd, Clinical Endocrinology, 71, 798–807

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We measured plasma intact PTH using the Elecsys 2010 immunoassay (Roche Diagnostics, Basel, Switzerland). The interand intra-assay coefficients of variation (CV) were less than 6% and 2%, respectively. We measured plasma 25OHD by enzyme-immunoassay (IDS, Phoenix, AZ, USA). The intra- and interassay CV were 6% and 7%, respectively. However, in our normal controls, 25OHD was measured using an equilibrium radioimmunoassay (RIA) (DiaSorin Inc., Stillwater, MN, USA) with inter- and intra-assay CV values of 13% and 10%, respectively. In order to be comparable to the IDS method, the DiaSorin results were adjusted by the formula: Y(nmol/l) = 1Æ23 · X(nmol/l) + 4Æ7 based on double measurements in 123 patients.5 We measured plasma 1,25(OH)2D by RIA (IDS, Phoenix) with the intra- and interassay CV from 10% and 12%, respectively. In our normal controls, we measured plasma 1,25(OH)2D by using the RIA (Nichols Institute, San Clemente, CA, USA) with intraand interassay CV values, both of 11%. In order to be comparable to the IDS method, the Nichols results were adjusted by the formula: Y(pmol/l) = 1Æ138 · X(pmol/l) + 3Æ9, based on double measurements in 74 patients.5 We constructed normal 95% confidence intervals for these variables. We measured alkaline phosphatase (AP) by the IFCC (International Federation of Clinical Chemistry) standardized, spectrophotometrical method, 37 C, Aeroset (Abbott Laboratories, Abbott Park, IL, USA) and Pyridinoline cross-linked amino-terminal telopeptide of collagen type I (U-NTx) in a second void morning spot urine by an immunometrical method (Vitros, Ortho Clinical Diagnostics, Inc., UK) and expressed as U-NTx/U-creatinine ratio (nmol/mmol). All the above mentioned measurements were performed in nonfasting individuals. We performed dual-energy X-ray absorptiometry (DXA) on the lumbar spine (L1–L4), the total hip, the forearm and whole body using Hologic QDR scanning equipment (Hologic, Waltham, MA, USA). We present our data as total body bone mineral content (BMC, g), together with BMD T- and Z-scores. We used the common normal material provided by the manufactures database to calculate BMD T- and Z-scores. We defined osteoporosis by Tscores 50 years 24H-U-Calcium (mmol) # $ Calcium/creatinine clearance ratio

66 66 66 66 66 66 66 66 66 66 66 60 66 26 40 66 53 17 14 22 65 22 43 65

50 (17–83) 66Æ7 1Æ68 (1Æ52–1Æ90) 68Æ8 (50Æ1–134Æ5) 23Æ8 (18Æ2–39Æ3) 1Æ41 (1Æ32–1Æ70) 2Æ66 (2Æ46–3Æ09) 2Æ69 (2Æ54–3Æ16) 70 (38–132) 5Æ3 (2Æ5–20Æ8) 0Æ90 (0Æ49–1Æ39) 73Æ0 (31–165) 57 (18–154) 74Æ5 (35–154) 50 (18–127) 126 (56–307) 37 (12–205) 30 (12–205) 49 (17–101) 50 (14–166) 2Æ6 (0Æ6–9Æ5) 2Æ6 (1Æ1–7Æ1) 2Æ5 (0Æ6–9Æ5) 0Æ006 (0Æ002–0Æ026)

Table 2 depicts differences between FHH and PHPT patients. The FHH group was younger, taller and leaner and had lower plasma creatinine (2P = 0Æ04), PTH (2P < 0Æ01) and 1,25(OH)2D (2P < 0Æ01) than the PHPT group, while the plasma levels of calcium, phosphate and 25OHD did not differ statistically between the groups. In total, 27% of PHPT patients had increased levels of AP and 14% had increased urinary NTx/creatinine ratio. Both plasma AP and the urinary NTx/creatinine ratio were significantly

95% reference values

Outside 95% reference values

1Æ15–1Æ30 2Æ20–2Æ55 2Æ20–2Æ52 44–115 1Æ6–6Æ9 0Æ80–1Æ50 35–105 18–110* 43–110* 18–85* 39–220*

66 [i] 57 [i] 66 [i] 1 [d], 1 [i] 15 [i] 16 [d] 2 [d], 6 [i] 6 [i] 2 [d], 3 [i] 4 [i] 2 [i]

21–83 17–94 26–124

1 [d], 1 [i] 0 [d], 1 [i] 1 [d], 2 [i]

2Æ0–9Æ0 2Æ0–7Æ0 †

5 [d], 0 [i] 11 [d], 3 [i]

Table 1. Clinical characteristics of 66 patients with familial hypocalciuric hypercalcaemia. Biochemical values are compared with normal laboratory reference values

[i] Increased values. [d] Decreased values. *Reference values are based on 46 healthy controls matched to FHH patients with respect to age (±5 years), sex and season, and collected during summer (N = 21) and winter (N = 25) periods. †See16.  2009 Blackwell Publishing Ltd, Clinical Endocrinology, 71, 798–807

The skeleton in FHH patients Table 2. Comparison of descriptive and biochemical variables between patients with familial hypocalciuric hypercalcaemia (FHH) and with primary hyperparathyroidism (PHPT)

FHH

Age (years) Females (%)† Height (m)* Body weight (kg)* BMI (kg/m2)* P-Calcium ion (mmol/l)* P-Calcium total (mmol/l)* P-Calcium alb. adj. (mmol/l)* P-Creatinine (lmol/l)* P-PTH (pmol/l)* P-Phosphate (mmol/l) P-Alkaline phosphatase (U/l)* P-Alkaline phosphatase (U/l)‡ P-25OHD (nmol/l)* P-1,25(OH)2D (pmol/l)* U-NTx/Creatinine ratio* U-NTx/Creatinine ratio‡ 24H-U-Calcium (mmol)* Calcium/creatinine clearance ratio* Lumbar spine BMD, Z-score T-score < )2Æ5 (%)† Total hip BMD, Z-score T-score