[Hyperhomocysteinemia and schizophrenia: case control study]

Homocysteine (Hcys) is a sulphur-containing amino acid that has been widely investigated for its putative role in neuropsychiatric disorders. Elevated plasma homocysteine levels have been associated with schizophrenia. Among other factors, low folate and vitamin B12 levels have been implicated in the increase in homocysteine. The aim of the study was to determine plasma Hcys, folate and vitamin B12, and the frequency and severity of hyperhomocysteinemia in patients with schizophrenia, and to investigate the association between Hcys and clinical features and its relationship with folate and vitamin B12 levels.

This was a case-control study carried out on 61 (54 males and seven females, mean age=33.3 ± 9.2) inpatients with chronic schizophrenia according to DSM-IV criteria and 46 (25 males and 21 females, mean age=45.9 ± 14.2) healthy controls. Most of patients (90.2%) were treated by first generation antipsychotics with a mean daily dosage of 401.6 mg chlorpromazine equivalents. Total homocysteine serum levels were determined quantitatively by fluorescence-polarization immunoassay (FPIA) with an AxSYM analyzer™ (Abbott). Quantitative vitamin B12 and folate serum levels were measured with an Elecsys 2010 analyzer™ (Roche Diagnostics). Differences between patients and controls were examined using a two-way Ancova with gender and diagnosis as independent variables, adjusting for age.

Patients with schizophrenia showed higher plasma Hycs and lower plasma folate than controls (mean=16.1 μmol/L in patients versus 10.9 μmol/L in controls; P=0.028 for Hycs and 4.2 μg/L in patients versus 8.2 μg/L in controls; P<0.001 for folate). Patients and controls did not differ in vitamin B12 levels. Both male and female patients had increased plasma Hcys compared to controls. Hyperhomocysteinemia (Hcys levels>15 μmol/L) was present in 34.4% of the patients versus 15.2% in controls. The prevalence of moderate hyperhomocysteinemia (Hcys levels: 15-29 μmo/L) was 26.2% and that of intermediate hyperhomocysteinemia (Hcys levels: 30-100 μmol/L) was 8.2%. In patients with schizophrenia, plasma Hcys was not correlated with age (r=0.07; P=0.56), duration of illness (r=-0.04; P=0.78) and did not differ with gender and clinical sub-types. Moreover, plasma Hcys was higher in patients without family history of psychiatric disorders (19.2 μmol/L) versus 12.7 μmol/L in patients with family history of psychiatric disorders (P=0.032). Concerning therapeutic features, plasma Hcys did not differ with type of antipsychotic and was not related to daily dosage of antipsychotics. A negative correlation was found between plasma Hcys and vitamin B12 levels (r=-0.26; P=0.04).

These results confirm an increase of Hcys levels in schizophrenic patients and suggest that it is associated with absence of family history of psychiatric disorders and with low vitamin B12 levels. Hyperhomocyteinemia could be related to the pathophysiology of aspects of this illness. Homocysteine should be considered as a factor to consider in monitoring and management of patients with schizophrenia.