Clinical Biochemistry of Domestic Animals (Sixth Edition) - UMK ...

III. Pathogenesis
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cellular organelles and may deform the nuclear outline.
As the process continues, the affected cells enlarge, which
is one cause of organomegaly. Just as with the CNS, cartilage,
and bone, pathophysiology is probably not solely
related to the increase in the cell, tissue, or organ size. The
storage of GAGs within the mitral heart valve causes the
normally fusiform cells to become rounded ( Fig. 24-6 ).
This, in turn, causes the valve leaflet and cordae tendinea
to become thick ( Fig. 24-7 ), interfering with normal valve
function and producing mitral regurgitation. Similarly,
storage within the cells of the cornea ( Fig. 24-8 ) results
in reflection and refraction of light, producing the cloudiness
observed grossly and by ophthalmoscopy ( Fig. 24-9 ).
However, in the cornea there is also an abnormality in collagen
biosynthesis resulting in larger fibrils that are more
widely spaced than normal ( Alroy et al. , 1999 ), and the
cornea of the MPS VI cat, rather than being thicker because
of increased cell size, is thinner than normal ( Aguirre et al. ,
1992 ).
In many LSDs, the CNS contains swollen neurons
( Fig. 24-10 ) with lysosomes that contain lamellar substrate
FIGURE 24-8 A light micrograph of the posterior cornea from a cat
with MPS VI illustrating the highly vacuolated keratocytes. Bar 25u.
FIGURE 24-6 An electron micrograph of a cell from the mitral heart
valve from a cat with MPS I. Note the extreme number of cytoplasmic
vacuoles, the loss of recognition of other organelles, and the deformed
nuclear outline. Bar 3u.
FIGURE 24-9 The appearance of the retina with indistinct optic disc
and vessels of an MPS I cat as seen through the cloudy cornea.
FIGURE 24-7 The mitral valve from a cat with MPS I illustrating the
thickened valve leaflets and cordae tendineae .
FIGURE 24-10 A light micrograph of swollen neurons in the facial
nucleus in the brain of a cat with MPSI. Bar 25u.