Abstract
Achondroplasia is a condition characterized by a genetic mutation affecting long bone endplate development. Current data suggests that the bone mineral content (BMC) and bone mineral density (BMD) of achondroplasic populations are below age matched individuals of average stature (controls). Due to the disproportionate limb-to-torso length compared to controls however, the lower BMC and BMD may be nullified when appropriately presented. The aim of this study was to measure whole-body and segmental body composition in adult males with achondroplasia (N = 10, 22 ±3 yrs), present data relative to whole-body and whole-limb values and compare all values to age matched controls (N = 17, 22 ±2 yrs). Dual X-ray absorptiometry (DEXA) was used to measure the in vivo mass of the whole-body and 15 segments, from which BMD, BMC, fat free mass (FFM) and body fat mass were measured. BMC of lumbar vertebrae (L1-4) was also measured and presented as a volumetric BMD (BMDVOL). The achondroplasic group had less BMC, BMD and FFM, and more body fat mass than controls as a whole-body measure. The lower achondroplasic BMC and BMD was somewhat nullified when presented relative to whole-body and whole-limb values respectively. There was no difference in lumbar BMDVOL between groups. Whole-body BMD measures presented the achondroplasic group as ‘osteopenic’. When relative to whole-limb measures however, achondroplasic BMD descriptions were normal. Further work is needed to create a body composition database for achondroplasic population’s, or for clinicians to present achondroplasic body composition values relative to the whole-limb.
Highlights
There was no difference in fat mass between groups (P = 0.447), but the achondroplasic group had a higher body fat percentage than controls (P < 0.001, Table 1)
The total mass of the all achondroplasic segments was lower than controls (P < 0.001) and there were significant effects between groups’ bone mineral content (BMC), bone mineral density (BMD), fat free mass (FFM) and body fat mass (P < 0.001, Table 2)
The findings show that adult achondroplasic males have less BMC, BMD and FFM than controls at the whole-body and segmental level, but body fat masses are the same as controls
Summary
Achondroplasia is the most common genetic form of dwarfism and is classically characterized by disproportionate limb-to-torso length and shorter stature (< 1.47 m) compared to persons of average stature without a form of dwarfism (hereafter referred to as ‘controls’). Achondroplasia is brought about by a fibroblast mutation resulting in shorter long-bones which presents a ‘disproportionate’ limb-to-torso lengths compared to controls [1,2,3,4,5,6]. Despite the available data on the condition, little quantitative confirmation of body composition (here defined as bone mineral content (BMC), bone mineral density (BMD), fat mass and fat free mass (FFM)) has been made. The participant inclusion criteria and in vivo body mass evaluation methods used in these studies are not robust enough to allow appropriate comparisons within achondroplasic populations or to commonly used reference data (e.g. controls)
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