Skeletal Radiol (2005) 34: 727–735 DOI 10.1007/s00256-005-0933-8 SCIENTIFIC ARTICLE G. Guglielmi F. de Terlizzi I. Torrente R. Mingarelli B. Dallapiccola Received: 19 October 2004 Revised: 22 March 2005 Accepted: 14 April 2005 Published online: 6 July 2005 # ISS 2005 Quantitative ultrasound of the hand phalanges in a cohort of monozygotic twins: influence of genetic and environmental factors Abstract Objective: Our objective was to evaluate the similarities and differences in bone mass and structure between pairs of monozygotic twins as measured by means of the quanti- tative ultrasound (QUS) technique. Design: A cohort of monozygotic twins was measured by QUS of the hand phalanges using the DBM sonic bone profiler (IGEA, Carpi, Italy). The parameters studied were ampli- tude-dependent speed of sound (AD-SoS), ultrasound bone profile index (UBPI), signal dynamics (SDy) and bone transmission time (BTT). Linear correlation coefficients, multi- variate linear analysis and the ANOVA test were used to assess intrapair associations between vari- ables and to determine which factors influence the intrapair differences in QUS variables. Patients: One hun- dred and six pairs of monozygotic twins were enrolled in the study, 68 females and 38 males in the age range 5 to 71 years. Results: Significant intrapair correlations were obtained in the whole population and separately for males and females, regarding height (r =0.98–0.99, p <0.0001), weight (r =0.95–0.96, p <0.0001), AD-SoS (r =0.90–0.92, p <0.0001), BTT (r =0.94–0.95, p <0.0001) and other QUS parameters (r >0.74, p <0.0001). Multivariate analysis revealed that intrapair differences between AD-SoS, SDy, UBPI and BTT are significantly influenced by age in the whole population and in the female population. Furthermore, the ANOVA test showed, for the female group, a significant increase in the intrapair differences in SDy and UBPI above 40 years. Conclusions: A relative contribution of genetic factors to skeletal status could be observed by phalangeal QUS measurement in monozygotic twins. A significant increase in the intrapair difference in QUS parameters with increasing age and onset of menopause also suggests the importance of environmental fac- tors in the female twin population. Keywords Quantitative ultrasound . Hand phalanges . Twins . Bone tissue . Bone mass regulation Introduction Osteoporosis is a multifactorial disease with both genetic and environmental determinants [1]. Several studies have already shown the influence of particular genes on the mechanism of bone resorption and bone formation [2– 6]; genetic influence is also the main explanation of the different incidence of osteoporosis among white and black populations [7]. Furthermore, the higher correlation level of osteocalcin in homozygotic twins compared with dizy- gotic twins indicates a strong genetic component in bone homeostasis [8]. On the other hand, it is already well known that in the same way many environmental factors, such as diet, drugs, exercise and coexisting diseases may contribute to the regulation of bone metabolism [6]. G. Guglielmi (*) . B. Dallapiccola Department of Radiology, Scientific Institute Hospital “Casa Sollievo della Sofferenza”, San Giovanni Rotondo, Italy e-mail: guglielmi_g@hotmail.com Tel.: +1-0882-410542 F. de Terlizzi IGEA Biophysics Lab, Carpi, Italy I. Torrente . R. Mingarelli . B. Dallapiccola Mendel Institute, Rome, Italy