**Question:** A female with recurrent abortions and isolated prolonged APTT is most likely associated with:

**Core Concept:** Prothrombin time (PT), activated partial thromboplastin time (aPTT), and their normal ranges are important coagulation tests that evaluate the intrinsic and extrinsic coagulation pathways, respectively. Prolonged aPTT indicates a defect in the intrinsic pathway.

**Why the Correct Answer is Right:** The correct answer (C) is related to Factor V Leiden (FVL) mutation. Factor V Leiden is a common inherited thrombophilia (increased risk of thrombosis). It is a mutation in the F5 gene, which codes for the protein Factor V. Factor V is essential for the activation of prothrombinase complex during the intrinsic coagulation pathway.

In individuals with Factor V Leiden mutation, the protein Factor V function is impaired, leading to a prolonged aPTT. The prolonged aPTT indicates a defect in the intrinsic pathway, which is consistent with Factor V Leiden mutation.

**Why Each Wrong Option is Incorrect:**

A. Factor V Leiden is not a specific cause of isolated prolonged aPTT without aPTT prolongation. Other causes of isolated prolonged aPTT, such as deficiency of protein C, protein S, or antithrombin III, are more likely when the aPTT is also prolonged.

B. Factor V Leiden is not a specific cause of recurrent abortions. Other thrombophilias, antiphospholipid syndrome, and specific anti-phospholipid antibodies are more likely when there are recurrent abortions.

D. Factor V Leiden is not exclusively inherited. Acquired causes, such as medications (e.g., heparin, insulin) and pregnancy, can also lead to a prolonged aPTT.

**Correct Answer:** C. Factor V Leiden (inherited thrombophilia) is most likely in this scenario, as it is a common cause of isolated prolonged aPTT and recurrent abortions. The inherited nature of Factor V Leiden helps distinguish it from the other options.