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A long term follow-up study of the development of hip disease in Mucopolysaccharidosis type VI
Esmee Oussoren1, Johannes H J M Bessems2, Virginie Pollet2
1Department of Pediatrics, Center for Lysosomal and Metabolic Diseases, Erasmus University Medical Center, Rotterdam, The Netherlands.
Abstract:
Hip problems in Mucopolysaccharidosis type VI (MPS VI) lead to severe disability. Lack of data on the course of hip disease in MPS VI make decisions regarding necessity, timing and type of surgical intervention difficult. We therefore studied the development of hip pathology in MPS VI patients over time. Data were collected as part of a prospective follow-up study. Standardized supine AP pelvis and frog leg lateral radiographs of both hips were performed yearly or every 2years. Image assessment was performed quantitatively (angle measurements) and qualitatively (hip morphology). Clinical burden of hip disease was evaluated by physical examination, six minute walking test (6MWT) and a questionnaire assessing pain, wheelchair-dependency and walking distance. A total of 157 pelvic radiographs of 14 ERT treated MPS VI patients were evaluated. Age at first image ranged from 2.0 to 21.1years. Median follow up duration was 6.8years. In all patients, even in the youngest, the acetabulum and os ilium were dysplastic. Coverage of the femoral head by the acetabulum improved over time, but remained insufficient. While the femoral head appeared normal in the radiographs at young age, the ossification pattern became abnormal in all patients over time. In all patients the distance covered in the 6MWT was reduced (median Z scores -3.3). Twelve patients had a waddling gait. Four patients were partially wheelchair-dependent and ten patients had limitations in their maximum walking distance. In conclusion, clinically significant hip abnormalities develop in all MPS VI patients from very early in life, starting with deformities of the os ilium and acetabulum. Femoral head abnormalities occur later, most likely due to altered mechanical forces in combination with epiphyseal abnormalities due to glycosaminoglycan storage. The final shape and angle of the femoral head differs significantly between individual MPS VI patients and is difficult to predict.
Insights
Hip abnormalities in Mucopolysaccharidosis type VI (MPS VI) are present from early childhood, causing significant disability. These progressive hip issues in MPS VI patients impact mobility and require careful management strategies.
Area of Science:
- Orthopedics
- Genetics
- Pediatrics
Background:
- Mucopolysaccharidosis type VI (MPS VI) is a rare genetic disorder.
- Hip problems in MPS VI patients lead to severe disability and impact quality of life.
- Limited data exists on the natural history of hip disease in MPS VI, hindering treatment decisions.
Purpose of the Study:
- To investigate the longitudinal development of hip pathology in patients with MPS VI.
- To correlate radiographic findings with clinical manifestations of hip disease.
- To provide data for informed surgical intervention timing and type.
Main Methods:
- Prospective follow-up study involving 14 enzyme replacement therapy (ERT)-treated MPS VI patients.
- Annual or biennial pelvic and hip radiographs (AP pelvis, frog leg lateral) analyzed quantitatively and qualitatively.
- Clinical evaluation included physical examination, 6-minute walking test (6MWT), and questionnaires on pain, wheelchair use, and walking distance.
Main Results:
- All patients exhibited hip dysplasia (acetabulum and os ilium) from a young age.
- Acetabular coverage of the femoral head improved but remained insufficient over time.
- Femoral head ossification abnormalities developed later, alongside reduced 6MWT distances and gait disturbances.
Conclusions:
- Clinically significant hip abnormalities are a universal feature of MPS VI, evident early in life.
- Os ilium and acetabular deformities precede femoral head abnormalities, likely due to altered biomechanics and GAG storage.
- Individual variability in final femoral head morphology makes prediction challenging.
