Gene analysis of six cases of congenital protein S deficiency and functional analysis of protein S mutations (A139V, C449F, R451Q, C475F, A525V and D599TfsTer13).

Congenital deficiency of protein S (PS), an anticoagulant factor, leads to venous thrombosis, with onset predominantly beginning in adolescence. In the present study, gene analysis of six unrelated Japanese families diagnosed with congenital PS deficiency identified five missense mutations in the PROS1 gene - c.757C>T (Ala139Val; A139V), c.1346 G>T (Cys449Phe; C449F), c.1352G>A (Arg451Gln; R451Q), c.1424G>T (Cys475Phe; C475F) and c.1574C>T (Ala525Val; A525V) - and one frameshift mutation, c.2135delA (Asp599ThrfsTer13; D599TfsTer13). C449F, R451Q, A525V and D599TfsTer13 are novel mutations. Results from ELISA to measure PS antigen levels in culture supernatant showed that the A139V variant was similar to wild-type, but other variants showed reductions when compared with wild-type. Results from pulse-chase analysis confirmed that the A139V variant exhibited secretion equivalent to wild-type, but for the other variants, there was no extracellular secretion, and it had nearly all been degraded inside the cell within six hours. Results from pulse-chase analysis using proteasome inhibitors also showed that intracellular degradation of mutant protein was inhibited. Activity of the A139V variant was decreased to 71% of wild-type, and the phospholipid binding capacity fell to as low as 45%. These results suggest that although the A139V variant has normal secretion, it has abnormal phospholipid binding capacity, and therefore causes type II PS deficiency, in which PS activity is decreased. It is also thought that with the other variants, misfolding due to amino acid mutations causes nearly all PS to be degraded intracellularly, therefore leading to type I PS deficiency.

Causative genetic mutations for antithrombin deficiency and their clinical background among Japanese patients.

We summarize causative genetic mutations for antithrombin (AT) deficiency and their clinical background in Japanese patients. A total of 19 mutations, including seven novel mutations, were identified. We also summarize clinical symptoms of thrombosis, age at onset, family history, and contributing factors for thrombosis, and review the use of prophylactic anticoagulation in pregnant women with heterozygous type II heparin binding site defects (HBS) AT deficiency. The prevalence of thrombosis in probands with type I AT deficiency (88%) was double that observed in those with type II AT deficiency (50%). The prevalence of thrombotic episodes among family members was also higher for type I AT deficiency subjects (82%) than for those with type II AT deficiency (0%). The most common contributing factor for thrombosis among women with type I AT deficiency was pregnancy. Forty-five percent of women with type I AT deficiency developed thrombotic events before the 20th week of gestation. In contrast, women with type II (HBS) AT deficiency appear to be at a lower risk of thrombosis during pregnancy. In conclusion, thrombotic risk varies among different subtypes. Risk assessments based on genetic/clinical backgrounds may contribute to appropriate diagnosis, treatment, and prophylaxis for patients with AT deficiency.