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Are Adult Patients with Laron Syndrome Osteopenic? A Comparison between Dual-Energy X-Ray Absorptiometry and Volumetric Bone Densities

Endocrine Institute (C.A.B., V.E.), Rabin Medical Center, Beilinson Campus, Petah Tikva 49100, Israel; Nadrilony Institute (M.K.), Tel Aviv 52451, Israel; the Pediatric Endocrine and Diabetic Research Unit (Z.L.), Schneider Children’s Medical Center of Israel, Petah Tikva 49100, Israel; and Sackler School of Medicine (Z.L., C.A.B.), Tel Aviv University, Tel Aviv, 69978 Israel

Address all correspondence and requests for reprints to: Carlos Benbassat, M.D., Endocrine Institute, Rabin Medical Center, Beilinson Campus, Petah Tikva, Israel 49100. E-mail: carlosb{at}netvision.net.il.

Severe short stature resulting from a deficiency in IGF-I is a prominent feature of Laron syndrome (LS). Although low bone mineral density (BMD) has been noted in LS patients examined by dual energy x-ray absorptiometry (DEXA), this technique does not take volume into account and may therefore underestimate the true bone density in patients with small bones. The aim of the present study was to evaluate the BMD yielded by DEXA in our LS patients using estimated volumetric values. Volumetric density was calculated with the following formulas: bone mineral apparent density (BMAD) = bone mineral content (BMC)/(area)^3/2 for the lumbar spine and BMAD = BMC/area² for the femoral neck. The study sample included 12 patients (mean age, 43.9 yr; mean height, 123.7 cm). Findings were compared with 10 osteopenic subjects without developmental abnormalities (mean age, 56 yr; mean height, 164.8 cm) and 10 healthy control subjects matched for sex and age to the LS patients (mean height, 165.5 cm). BMAD in the LS group was 0.201 ± 0.02 g/cm³ at the lumbar spine and 0.201 ± 0.04 g/cm³ at the femoral neck; corresponding values for the osteopenic group were 0.130 ± 0.01 and 0.140 ± 0.01 g/cm³, and for the controls, 0.178 ± 0.03 and 0.192 ± 0.02 g/cm³. Although areal BMD was significantly lower in the LS and osteopenic subjects compared with controls (P < 0.02) at both the lumbar spine and femoral neck, BMAD was low (P < 0.01) in the osteopenic group only. In conclusion, DEXA does not seem to be a reliable measure of osteoporosis in patients with LS.

Abbreviations: BMAD, Bone mineral apparent density; BMC, bone mineral content; BMD, bone mineral density; DEXA, dual energy x-ray absorptiometry; GHD, GH deficiency; GHIS, GH insensitivity syndrome; LS, Laron syndrome; QCT, quantitative computed tomography.

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