Protein S Deficiency

Definition - What does Protein S Deficiency mean?

Protein S deficiency is a condition characterized by the lack of protein S, which is a naturally-occurring vitamin-K dependent blood thinner. Protein S deficiency is a rare condition, affecting about 1 in 500 people in the United States. Although it is usually hereditary, protein S deficiency may also be acquired. The hereditary form of protein S deficiency is inherited in an autosomal dominant fashion. This means that if one parent has the deficiency, each of their children will have a 50:50 chance of having a full-blown disease. Protein S deficiency can affect both males and females. The condition leads to recurrent pregnancy loss as well as recurrent IVF (in vitro fertilization) failure.

FertilitySmarts explains Protein S Deficiency

Protein S activates another blood thinner named protein C, which in turn degrades the activated forms of clotting factors V and VIII. Reduced breakdown of these clotting factors (as occurs with protein S deficiency) increases their levels, and consequently, augments blood’s vulnerability to clot excessively. These blood clots can form in both arteries and veins such as veins of the legs (deep vein thrombosis) and arteries of the brain.

Women with protein S deficiency also find it hard to get pregnant. This is because the clots tend to form in the vessels of the placenta and uterus. This not only negatively impacts implantation of the fertilized egg but if implantation is successful, deprives the developing baby of the nutrients and oxygen supply that it needs to survive. Recurrent pregnancy loss (RPL), is, therefore, expected with conditions like protein S deficiency. RPL is defined as 2 or more consecutive losses, most often occurring in the initial 3 months.

Improper function of the placenta can also result in preeclampsia and abruption. For this reason, women with a history of recurrent pregnancy loss, abruption, severe preeclampsia, and growth restriction of the fetus are usually tested for protein S deficiency.

Not only are spontaneous pregnancies prone to miscarry, but IVF failure is also likely to occur in women with infertility due to protein S deficiency. In fact, the largest percentage of failed IVF cycles is due to the lack of implantation caused by conditions like protein S deficiency.

The diagnosis is made by laboratory blood tests that measure protein S antigen levels and activity.

Individuals treated for protein S deficiency fall into 2 categories: one who have had a thrombotic event and the other who have no symptoms or complications but are carriers of the disease. The first group is treated with blood thinners like heparin. In the latter group, doctors may use preventive strategies if required.

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