Schizophrenia genetic variants are not associated with intelligence. Issue 12 (December 2013)

• Record Type: Journal Article
• Authors: van Scheltinga, A. F. Terwisscha; Bakker, S. C.; van Haren, N. E. M.; Derks, E. M.; Buizer-Voskamp, J. E.; Cahn, W.; Ripke, S.; Ophoff, R. A.; Kahn, R. S.
• Is Part Of: Psychological medicine. Volume 43:Issue 12(2013)
• Page Start: 2563
• Page End: 2570
• Publication Date: 2013-12
• Subjects: Psychiatry -- Periodicals; Medicine and psychology -- Periodicals; Clinical psychology -- Periodicals; 616.89
• DOI: 10.1017/S0033291713000196
• Languages: English
• ISSNs: 0033-2917

Abstract

<abstract abstract-type="normal"> <title> <x content-type="archive" xml:space="preserve">Abstract</x> </title> <sec id="sec_a1"> <title>Background</title> <p>Schizophrenia is associated with lower pre-morbid intelligence (IQ) in addition to (pre-morbid) cognitive decline. Both schizophrenia and IQ are highly heritable traits. Therefore, we hypothesized that genetic variants associated with schizophrenia, including copy number variants (CNVs) and a polygenic schizophrenia (risk) score (PSS), may influence intelligence.</p> </sec> <sec id="sec_a2" sec-type="methods"> <title>Method</title> <p>IQ was estimated with the Wechsler Adult Intelligence Scale (WAIS). CNVs were determined from single nucleotide polymorphism (SNP) data using the QuantiSNP and PennCNV algorithms. For the PSS, odds ratios for genome-wide SNP data were calculated in a sample collected by the Psychiatric Genome-Wide Association Study (GWAS) Consortium (8690 schizophrenia patients and 11 831 controls). These were used to calculate individual PSSs in our independent sample of 350 schizophrenia patients and 322 healthy controls.</p> </sec> <sec id="sec_a3" sec-type="results"> <title>Results</title> <p>Although significantly more genes were disrupted by deletions in schizophrenia patients compared to controls (<italic>p</italic> = 0.009), there was no effect of CNV measures on IQ. The PSS was associated with disease status (<italic>R</italic><sup>2</sup> = 0.055, <italic>p</italic> = 2.1 × 10<sup>−7</sup>) and with IQ in the entire sample (<italic>R</italic><sup>2</sup> = 0.018, <italic>p</italic> = 0.0008) but the effect on IQ disappeared after correction for disease status.</p> </sec> <sec id="sec_a4" sec-type="conclusion"> <title>Conclusions</title> <p>Our data suggest that rare and common schizophrenia-associated variants do not explain the variation in IQ in healthy subjects or in schizophrenia patients. Thus, reductions in IQ in schizophrenia patients may be secondary to other processes related to schizophrenia risk.</p> </sec> </abstract>