Complex sentence: In some people the cholesterol receptor is defective, uptake of cholesterol from the blood into liver cells is slow and cholesterol accumulating in the blood and can damage blood vessel walls resulting in strokes and heart attacks at a young age.
Split into simpler sentences: In some people the cholesterol receptor is defective, uptake of cholesterol from the blood into liver cells is slow and cholesterol accumulates in the blood. This receptor defect, if it did lead to blood vessel damage, would lead to observations of strokes and heart attacks at a young age.