Polygenic Heritability of Intelligence in First Cousins: Beneficial Cognitive Homozygosity and an Exploratory Estimate of Intelligence Quotient

• DOI: https://doi.org/10.22533/at.ed.0159672604061

• Palavras-chave: double cousins; identity by descent; cognitive homozygosity; polygenic heritability; GIP Genetic IQ; GIP MultiSource; exploratory IQ estimation; hippocampus CA1.

• Keywords: double cousins; identity by descent; cognitive homozygosity; polygenic heritability; GIP Genetic IQ; GIP MultiSource; exploratory IQ estimation; hippocampus CA1.

• Abstract:

  Exploratory estimation of intelligence quotient (IQ) in individuals without direct psychometric assessment can be grounded in the polygenic heritability model when genomic data from first-degree relatives and a high-consanguinity genealogical configuration are available, provided that the results are treated as suggestive probability ranges rather than psychometric measurements. This article examines the case of Fábio de Abreu Rodrigues, the double cousin of Fabiano de Abreu Agrela Rodrigues (IQ = 160, as measured by the Wechsler Scale, validated in Brazil and Portugal), using whole-genome sequencing data and microarray genotyping with imputation of shared parents: José Rodrigues Filho and Maria Ascenção de Abreu Rodrigues, Fabiano’s parents, whose biological siblings Carlos Roberto Rodrigues and Maria Inês de Abreu Rodrigues are Fábio’s parents. The double-cousin configuration establishes an identity by descent (IBD) coefficient of r = 0.25. The Mid-Parent Value (μ) was derived directly from the GIP Genetic IQs calculated by the GIP MultiSource protocol for the parents: Maria Ascenção = 135 (±10) and José Rodrigues = 125 (±10), resulting in μ = 130. Under these real-world data, the regression equation for the mean E(Y) = μ + r × (X − μ) yields a theoretical estimate of 137.5 points, already within the 130–145 range prior to any further adjustment. The analysis incorporates the clinical hypothesis of advantageous cognitive homozygosity postulated by geneticist Susana Massarani, discussing three recombination scenarios for Fábio: equivalent to Fabiano’s (maintained or elevated estimate), heterozygous (estimate reduced to 130–137), and with a compensatory epistatic effect (estimate elevated above the floor). The article includes a section on limitations that discusses the intrinsic constraints of individual IQ inference using indirect genomic methods.