OBJECTIVE: Congenital cleft palates are one of the most commonly occurring birth defects in the world, with recent studies reporting rates as high as 6.8 per 10,000 live births. The condition significantly impacts those children in many ways: feeding, airway maintenance, middle ear disease, and speech development. Despite efforts to surgically repair the cleft palate defect, about 15% of patients will have velopharyngeal insufficiency (VPI), regardless of the type of repair. We hypothesize that VPI in cleft palate patients may be due, at least in part, to muscular dysgenesis and inherent levator muscle dysfunction. METHODS: Six palates from 14-month-old female Spanish goats were used to perform this study: three control, non-clefted goat palates and three chemically-induced, congenitally-clefted goat palates. Levator veli palatini (LVP) muscles from each of the experimental groups were analyzed morphometrically at the cellular level using light microscopy and H&E staining. Cross-sections of the LVP were evaluated by myosin ATPase staining to determine slow and fast muscle fiber composition, and entire fascicles were assessed for myosin heavy chain content using Western blot analysis. In addition, congenitally-clefted and non-clefted 8-week-old goat palates were analyzed at the subcellular level using electron microscopy. RESULTS: The cleft palate LVP muscles demonstrated a disorganized pattern of fiber orientation compared to the control group under light microscopy. Under electron microscopy, sarcomeric patterns were disrupted and enlarged mitochondria were identified in the clefted muscles. Cross-sectional areas of the clefted palate muscle fibers (1987±739 µm²) were significantly greater than the areas of the non-clefted (1656±518 µm²) muscle fibers (p<0.0003). Myosin ATPase staining of muscle cross-sections showed significant differences (p<0.0001) between the two groups with clefted muscles containing both Type 1, slow-oxidative (29.3±10.6%) and Type 2, fast-glycolytic (70.7±10.6%) fibers while the normal muscles contained only Type 1 fibers (100%). This finding was confirmed using Western blot analysis of myosin heavy chains. CONCLUSIONS: Clear differences in muscle fiber orientation and fiber type exist between control and congenitally-clefted goat palates. These findings have enormous clinical implications. Perhaps, with this information, patients at risk for developing VPI may be identified earlier, and treatment can be adjusted accordingly.
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