Complex sentence: FCMD mainly affects the brain, eyes, and muscles, in particular, the disorder affects development of the skeletal muscles leading to weakness and deformed appearances, and brain development is blunted affecting cognitive functioning as well as social skills.
Split into simpler sentences: FCMD mainly affects the brain, eyes, and muscles. In particular, the disorder affects development of the skeletal muscles leading to weakness and deformed appearances, and brain development is blunted affecting cognitive functioning as well as social skills.