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Study Reveals Familial Patterns in Intelligence Among First Episode Psychosis Patients

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A recent study by a group of researchers from various European institutions looked into the connection between family intelligence quotients (IQ) and the risk of schizophrenia spectrum disorders (SSD). The study, published in the journal Schizophrenia Bulletin, explored the familiality of IQ among first-episode psychosis (FEP) patients and their first-degree relatives, revealing significant findings about cognitive similarities and potential genetic and environmental influences on mental health.

The familiality of cognitive traits, including IQ, has long been a subject of interest in understanding the genetic and environmental factors contributing to schizophrenia spectrum disorders. Previous studies have shown varying degrees of familial aggregation of IQ among patients with SSDs, suggesting a complex interplay between genetics and environment. The PAFIP-FAMILIAS project aimed to quantify the degree of IQ resemblance within families and investigate how these patterns correlate with the clinical profiles of FEP patients.

The study involved 129 FEP patients, 143 parents, and 97 siblings, all of whom underwent the same neuropsychological battery to assess their IQ and other cognitive functions. The researchers employed the Intraclass Correlation Coefficient (ICC) to estimate IQ-familiality and calculated the intra-family resemblance score (IRS) for each family. This score provided a quantitative measure of the similarity of IQ among family members.

The results revealed that IQ familiality among FEP patients was low to moderate, with an ICC of 0.259. Approximately 44.9% of the FEP patients showed a low IRS, indicating a significant discordance with their family IQ. Interestingly, these patients with low IQ and low familial resemblance were more frequently diagnosed with schizophrenia and demonstrated poorer premorbid adjustment during childhood and adolescence. In contrast, patients with low IQ but high familial resemblance exhibited the poorest performance in executive functions.

The study’s findings suggest that deviations from familial cognitive performance may be linked to specific pathological processes in SSD. Patients who do not reach their cognitive and familial potential might face adjustment difficulties from early childhood, possibly influenced by environmental factors. Conversely, patients with high phenotypic resemblance to their families may bear a more significant genetic burden for schizophrenia.

These results have profound implications for understanding the heterogeneity of psychotic manifestations. By stratifying patients based on their concordance or discordance with family neurocognition, researchers and clinicians can better comprehend the underlying mechanisms of psychosis and develop targeted prevention and treatment strategies.

One of the study’s main strengths is its use of comprehensive neuropsychological data from both FEP patients and their unaffected first-degree relatives, allowing for a robust estimation of IQ familiality. But the researchers acknowledged several limitations. The small size of some patient subgroups limited the statistical power, and the study’s findings cannot be generalised to all FEP patients due to the voluntary participation, which might have skewed the sample towards those with better cognitive and functional outcomes.

The study used the WAIS-III Vocabulary subtest to estimate IQ, which primarily measures crystallised intelligence, potentially overlooking other important aspects of cognitive ability. Future research should aim to include larger samples and explore genetic factors underlying IQ familiality to provide a more comprehensive understanding of these dynamics.

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