Ralph A. Gruppo

The plasminogen activator inhibitor-1 gene, hypofibrinolysis, and osteonecrosis.

In 59 patients with osteonecrosis of the hip, four genes associated with thrombophilia or hypofibrinolysis along with coagulation tests were studied to determine the pathoetiologic associations of heritable coagulation disorders with osteonecrosis. Patients did not differ from healthy control subjects for the thrombophilic Factor V Leiden, prothrombin, or methylenetetrahydrofolate reductase mutations. The plasminogen activator inhibitor-1 gene was shifted toward homozygosity for the 4G polymorphism; 41% of patients with osteonecrosis were homozygous for the 4G/4G polymorphism versus 20% of 40 healthy control subjects. The gene product of the 4G polymorphism, hypofibrinolytic plasminogen activator inhibitor activity, was higher in patients than in control subjects (median 19.2 versus 6.3 U/mL); 61% of patients had high plasminogen activator inhibitor activity (> or = 16.4 U/mL) versus 5% of control subjects. Stimulated tissue plasminogen activator activity (inhibited by plasminogen activator inhibitor activity) was lower in patients than in control subjects (3.10 versus 5.98 IU/mL); 31% of patients had low stimulated tissue plasminogen activator activity (< 2.28 IU/mL) versus 3% of control subjects. Heritable hypofibrinolysis conferred by the 4G/4G mutation of the plasminogen activator inhibitor-1 gene seems to be a major pathoetiology of primary osteonecrosis.

Legg-Perthes disease in three siblings, two heterozygous and one homozygous for the factor V Leiden mutation

A family is described with three-generation transmission of factor V Leiden (a thrombophilic mutation that causes resistance to activated protein C). Legg-Perthes disease developed in three siblings in this family. The male proband and his sister were heterozygous for the mutation and had unilateral hip disease at age 2 years. The brother, who had bilateral hip disease, was homozygous. This novel family provides compelling evidence for the pathoetiologic role of familial thrombophilia in Legg-Perthes disease.

Correlation of the C677T MTHFR genotype with homocysteine levels in children with sickle cell disease

Recently, a mild to moderate elevation in the plasma homocysteine (Hcy) level has been found to be an important risk factor for stroke. Homozygosity for a common mutation (C677T) in the gene encoding for the enzyme methylenetetrahydrofolate reductase (MTHFR) involved in Hcy metabolism has been associated with increased levels of Hcy. To determine the role of hyperhomocysteinemia in the pathogenesis of stroke in children with sickle cell disease (SCD), Hcy levels and C677T MTHFR genotype were determined in 40 patients homozygous for hemoglobin SS and compared with 197 healthy children. Eleven of 40 patients with SCD had a history of stroke. The prevalence of homozygosity for the C677T MTHFR variant was 5% in the patients with SCD. The median Hcy level was 5.8 micromol/L in the patients versus 5.4 micromol/L in the controls (Fishers, P > 0.05). There was no correlation of Hcy levels with the MTHFR genotype in patients with SCD. In patients with SCD and stroke, the median Hcy level was 4.8 micromol/L versus 6.0 micromol/L in those without stroke (P = 0.44, Mann-Whitney rank sum test). There was no difference in the proportion of patients with SCD with or without stroke who were homozygous for the C677T MTHFR mutation (0/11 versus 2/29; Fishers, P = 1.000). In conclusion, this study failed to demonstrate an elevation in plasma Hcy levels in children with SCD compared with normal controls. Furthermore, hyperhomocysteinemia did not seem to be a significant factor in the pathogenesis of stroke in children with SCD.

Hyperhomocysteinemia is associated with low plasma pyridoxine levels in children with sickle cell disease

Elevated plasma homocysteine levels have been shown to be a risk factor for endothelial cell damage and thrombosis, which are implicated in sickle cell disease (SCD)-related vaso-occlusion. The aim of this study was to determine the prevalence of hyperhomocysteinemia in SCD. Fasting and postmethionine load (PML) homocysteine, red cell folate, and the MTHFR C677T mutation were determined in 77 patients with SCD and 110 African-American controls. Plasma methylmalonic acid and pyridoxine levels were determined in 54 patients and all controls. For analysis, the subjects were divided into two age groups (2–10 years and 10.1–21 years). In both age groups, median PML homocysteine levels were significantly elevated in patients with SCD compared with controls. Fasting homocysteine levels were elevated in patients with SCD versus controls only in those older than 10 years. Hyperhomocysteinemia was noted in 38% of patients versus 7% in controls. Folate levels were higher among patients than controls and showed a significant negative correlation with PML homocysteine levels in patients with SCD. Pyridoxine levels in patients with SCD were significantly lower than in controls and showed a negative correlation with PML homocysteine levels. Among patients with SCD, pyridoxine deficiency was more common (62%) among those with hyperhomocysteinemia compared with those with normal homocysteine levels (30%). Homozygosity for the MTHFR C677T mutation was rare. These data suggest that children with SCD have significant hyperhomocysteinemia, associated with pyridoxine and relative folate deficiencies.