Bone Abstracts

Objectives: i) Describe bone mineral density (BMD) of children with MPS IV (Morquio disease), a rare genetic disorder which produces skeletal deformity, small stature and results in physical limitations such as the ability to walk.

ii) Examine fracture history and factors affecting bone health in Morquio.

iii) Describe technical issues encountered in assessing BMD by DXA in Morquio.

Methods: In this prospective cross-sectional study, BMD of the whole body (WB), lumbar spine (LS) and lateral distal femur (LDF) were acquired by DXA on a group of children with MPS IV(A) or MPS IV(B). Functional abilities, medical history, Tanner score, and laboratory results were reviewed. Radiologic images of the lateral spine, including X-rays and IVA by DXA were used to aid in correct region of interest placement on the LS DXA and in interpretation. Age and gender-matched norms were used to calculate Z-scores.

Results: Ten children (eight females) with a mean age of 11.8 years (range 3.3–18 years) participated in the study. Both subtypes of Morquio (A and B) were represented. While every subject was weightbearing, half were full-time ambulators. Whole body could be obtained on only four subjects due to respiratory compromise caused by the position, presence of hardware or positioning difficulties. Mean WB Z-score was −2.2 (range −0.6 to −4). Mean LS BMD Z-score was −3.5 (range −0.8 to −6.9) with seven subjects exhibiting low BMD. Technical issues encountered with this metabolic condition included kyphosis at the thoracolumbar junction and wedge configuration of the vertebrae. Lateral views of the spine were needed for correct identification of vertebrae. LDF BMD Z-scores at all regions were low, with mean Z-scores of −2.6, −2.5, and −2.8 at regions 1, 2, and 3 respectively. Only one fracture was reported and was due to trauma of the hand.

Conclusion: Children with Morquio exhibited low BMD at all sites measured. Despite the low BMD and skeletal dysplasia, fractures were not reported. WB DXA was not well tolerated or feasible. Anatomical abnormalities of the spine and technical limitations of DXA make assessment of the LS challenging.