In patients with moderate to severe MPS I, coarse facial features develop slowly in the first year and by two years of age are usually fairly obvious (Image 1).
Image 1 - Coarse facial features -
Courtesy of E. Kakkis, MD
This coarseness, which leads to the loss of fine detail in the infant's facial features, is caused by storage of glycosaminoglycans in the orofacial region, as well as by underlying facial bone dysostosis. Thickened nostrils, lips, and ear lobules and enlargement of the tongue are all characteristics that become progressively more evident. Facial and body hypertrichosis is often seen by 24 months of age, at which time the facial and scalp hair may be coarse, straight and thatch-like. Children with severe MPS I generally have large heads, in part a consequence of the thickened calvaria that also produces a characteristic cranial appearance. The head tends to be longer than normal from front to back (scaphocephaly) and the forehead is often particularly prominent, or prow-shaped, as a consequence of cranio-synostosis.
The physical appearance of mildly affected individuals with attenuated MPS I is quite variable (Image 2).
Image 2 - Young adult woman with attenuated
phenotype of MPS I (also known as Scheie disease)
(Photo used with patient permission)
Coarse facial features that are so characteristic of children with severe MPS I are less obvious in mildly affected individuals. These individuals may have short necks, broad mouths, square jaws and receding chins (micrognathia). These mildly affected individuals, while their stature and height may be unaffected, often have a stocky build and their trunks may be short in relation to their limbs. Patients with attenuated MPS I may have variable degrees of slowed growth. Arthropathy is universal and leads to fixed deformities of joints; typically individuals exhibit a characteristic joint contracture deformity (Image 3).
Image 3 - Joint Contractures
Courtesy of J.E. Wraith, MD
Genetic counselors are health professionals who are trained to help families understand genetic disorders such as MPS I disease. A genetic counselor can help you determine if you are a carrier of a gene defect that causes MPS I and can provide valuable information and support for family planning. To learn more, click here.