Imprinting, the X-chromosome, and the male brain : Explaining sex differences in the liability to autism

• Published in: Pediatric research Vol. 47; no. 1; pp. 9 - 16
• Main Author: SKUSE, D. H
• Format: Journal Article
• Language: English
• Published: Hagerstown, MD Lippincott Williams & Wilkins 2000
• Subjects: Adult and adolescent clinical studies; Autistic Disorder - genetics; Biological and medical sciences; Brain - physiopathology; Female; Genomic Imprinting; Humans; Male; Medical sciences; Other psychotic disorders; Phenotype; Psychology. Psychoanalysis. Psychiatry; Psychopathology. Psychiatry; Psychoses; Sex Factors; X Chromosome; Human; Autism; Risk factor; Sex; Regulator gene; Male; Developmental disorder; X-Chromosome; Sexual dimorphism; Genetic determinism; Child; Genomic imprinting
• ISSN: 0031-3998; 1530-0447
• DOI: 10.1203/00006450-200001000-00006

Males are at least four times more likely to develop autism than females. Among relatives with a broader autistic phenotype, males predominate too. Autism is a highly heritable disorder, yet genome scans have not revealed any predisposing loci on the sex chromosomes. A nongenetic explanation for male vulnerability, such as exposure to prenatal androgens, is unlikely for a variety of reasons. A novel genetic mechanism that resolves many of the outstanding difficulties is outlined here. The imprinted-X liability threshold model hypothesizes that the threshold for phenotypic expression of many autistic characteristics is influenced by an imprinted X-linked gene(s) that is protective in nature. Imprinted genes are known to play an important role in normal fetal and behavioral development. The gene is expressed only on the X-chromosome that is inherited from the father and raises the threshold for phenotypic expression. It is normally silenced when transmitted maternally. Because only females have a paternal X-chromosome, the threshold for phenotypic expression is higher in them than in males. Evidence for the existence of the genetic locus was found in a study of females with X-monosomy (Turner's syndrome) in which females had either a single paternal or maternal X-chromosome. Identifying the sites of action of this X-linked gene could lead to the discovery of autosomal loci that confer more directly a predisposition to autism.