Fig. 5. Abnormalities of the cilia (1) dynein arms abnormalities involve either partial or complete absence of outer dynein arm/inner dynein arm, (2) radial spokes abnormalities including the absence of spokes or deviated central microtubules, (3) inappropriate directionality of cilia, caused by partial or complete absence of the central microtubules, and (4) abnormal number of peripheral microtubules. Atypical arrangements for example 8+1, 8+2, 8+3, or 7+2 have been observed under the microscope on cross-section.