Pregnant women with hypothyroxinemia — low levels of the thyroid hormone thyroxine — are at greater risk of having babies who later develop cognitive abnormalities similar to those seen in schizophrenia, according to a new study published in the journal Biological Psychiatry.
Hypothyroxinemia is also associated with preterm birth, another risk factor for schizophrenia.
For the study, researchers examined thyroxine levels in archived serum samples from 1,010 mothers of children with schizophrenia and 1,010 matched control mothers.
The serum samples were collected during the first and early second trimesters of pregnancy as part of the Finnish Maternity Cohort. The findings show that 11.8 percent of people with schizophrenia had a mother with hypothyroxinemia, compared with 8.6 percent of people without schizophrenia. The finding was statistically significant.
This suggests that children of mothers with hypothyroxinemia during pregnancy have increased odds of developing schizophrenia. The association remained even after adjusting for variables strongly related to schizophrenia such as maternal psychiatric history and smoking.
First author Dr. David Gyllenberg of the University of Turku, Finland, thinks the importance of this paper is that it “links the finding to an extensive literature on maternal hypothyroxinemia during gestation altering offspring brain development.”
Senior author Dr. Alan Brown, professor of psychiatry epidemiology at Columbia University Medical Center, emphasized that “this work adds to a body of literature suggesting that maternal influences, both environmental and genetic, contribute to the risk of schizophrenia.”
“Although replication in independent studies is required before firm conclusions can be drawn, the study was based on a national birth cohort with a large sample size, increasing the plausibility of the findings,” said Brown.
While the study did not address a cause for the association, it did find that adjusting for preterm birth lowered the association between hypothyroxinemia and schizophrenia, suggesting that preterm birth may play a role in the increased risk.
And while the study focused on patients with schizophrenia, the researchers caution that the finding may not be solely specific to schizophrenia. They say that hypothyroxinemia should be studied as a risk factor for other neurodevelopmental disorders as well, such as bipolar disorder and autism.
Their findings are expected to encourage further research examining how hypothyroxinemia causes neurodevelopmental abnormalities and ultimately contributes to risk of mental illnesses that arise during development.
“As rodent models of maternal hypothyroxinemia have been developed and schizophrenia is largely considered a disorder of brain development, I hope this paper can inform future animal studies examining molecular and cellular deviations that are relevant to schizophrenia,” said Gyllenberg.