Quantitative ultrasound and peripheral bone densitometry in patients with genetic disorders.

The aim of the study was comparison of quantitative ultrasound and densitometric peripheral measurements in subjects with genetic disorders. The study included 52 subjects (35 boys and 17 girls) in mean age 13.1 +/- 4.8 y. Patients with following disorders were evaluated: Down syndrome (n = 21), Martin-Bell syndrome (n = 14) and other (n = 17). There were no additional factors potentially influencing bone metabolism. Bone status was assessed by quantitative ultrasound at the hand phalanges using DBM Sonic 1200 (IGEA, Italy), which measures amplitude-dependent speed of sound (Ad-SoS [m/s]) and bone densitometry at the calcaneus and forearm by the use of PIXI (GE, USA), which measures bone mineral density (BMD, g/cm2). Ad-SoS correlated significantly with forearm and calcaneus BMD in the whole group (r = 0.66, p < 0.000001 and r = 0.51, p < 0.0001, respectively), in females (r = 0.58, p < 0.05 and r = 0.5, p < 0.05) and in males (r = 0.70, p < 0.000001 and r = 0.54, p < 0.001). Calcaneus BMD correlated with wrist BMD in the whole group, in females and males: r = 0.66, p < 0.000001, r = 0.67, p < 0.01 and r = 0.75, p < 0.0001, respectively. These coefficients of correlation were compared and did not reveal significant differences in the whole group and in the gender subgroups. ROC analysis of Ad-SoS values versus calcaneus and forearm BMD showed area under curve 0.89 for forearm BMD and 0.79 for calcaneus BMD (subjects with Ad-SoS T-score below -3.2 were considered as abnormal). Age correlated significantly with Ad-SoS, forearm and calcaneus BMD (r ranged from 0.53 to 0.9, p from 0.05 to 0.000001). In all patients and males, age more strongly influenced Ad-SoS than calcaneus BMD (p < 0.05). Also, body weight and height correlated significantly with Ad-SoS, forearm and calcaneus BMD, except for correlation between forearm BMD and height in female patients (r from 0.58 to 0.84, p < 0.05). Generally, in multiple stepwise regression analysis of age and body size on skeletal parameters, age had positive influence, and body size was a positive or a negative factor. In conclusion, both quantitative ultrasound and peripheral densitometry may be recommended for the assessment of skeletal status in subjects with genetic disorders, although measurements of phalanges seem to be more sensitive for detecting age-related bone changes.