Which complement deficiency is known to be inherited as X-linked?

Properdin deficiency is indeed an X-linked complement deficiency. Properdin is a crucial component of the complement system that helps regulate the alternative pathway of complement activation. It is the only known complement protein that is X-linked, which means that males with the deficiency will typically express the symptoms of the condition, while females may be carriers without significant effects due to the presence of another X chromosome.

Understanding the context of the complement system is important here. Other deficiencies related to the complement system, such as Factor H deficiency, C3 deficiency, and C1 esterase inhibitor deficiency, are inherited through different mechanisms—Factor H and C3 deficiencies are usually inherited in an autosomal recessive manner, while C1 esterase inhibitor deficiency is inherited in an autosomal dominant manner. By knowing the inheritance patterns of these deficiencies, it's clear why properdin deficiency stands out as the X-linked option.