Rare Genomic Deletions Underlying Schizophrenia and Related Neurodevelopmental Disorders
Year: 2014
Type: dissertation
Study design: Observational Study
Abstract: Severe mental disorders including schizophrenia often segregate within the same families. Twin and family studies suggest that this co-occurrence is largely genetic, which implies that the different mental disorders have a shared genetic background. Some symptomatic features, such as cognitive impairment also manifest to a variable degree in the majority of severe mental disorders. Cognitive impairment occurs already before the onset of the disease and healthy family members of patients perform worse in cognitive tests than do the general population, which suggests that the cognitive impairment is indicative of genetic loading of the disease. Furthermore, the cognitive impairment persists throughout the disease and is associated with poorer outcome. This led us to hypothesize that the genetic architecture of schizophrenia is more similar to developmental disorders than had been considered earlier. Specifically, we hypothesized that rare high impact genetic variants play a role in the genetic risk for schizophrenia. Rare recurrent large-scale structural variation has long known to cause developmental syndromes, such as Prader-Willi syndrome or Velocardiofacial syndrome. In this study we investigated the role of large-scale chromosomal copy number variants in the genetic background of schizophrenia and other traits hypothesized to reflect abnormal neuronal development. In this study four chromosomal deletions on 1q21, 15q11.2, 15q13.3 and 22q11.2 were identified to be associated with schizophrenia. Three of the deletions occurred recurrently, whereas the deletion on 22q11.22 was a founder mutation enriched especially in the North-East region of Finland. On a population level, carriers of large deletions were found to have more intellectual disability or sub-normality (IQ<85) than non-carriers. Also milder learning difficulties as measured by repeated grades in school were more common among carriers of large deletions. The four deletions specifically identified as associating with schizophrenia are linked to variable phenotypes with the strongest effect manifesting in intellectual disabilities. The regional enrichment of the deletion on 22q11.22 also enabled the assessment of recessive effects related to the deletion. Four individuals, all presenting with a neurodevelopmental phenotype and/or schizophrenia, were identified as homozygous for the deletion. This deletion overlaps one gene encoding for topoisomerase 3 beta (TOP3β) that forms a protein complex with FMRP, the fragile X mental retardation protein, via tudor domain containing 3 (TDRD3) protein. The results of this study imply that rare high risk variants are present in a sub set of schizophrenia patients and that these variants are shared with developmental disorders. The study also demonstrates that special populations such as population isolates can provide useful study designs in identifying rare genetic risk variants, especially with recessive effects for complex traits.
Source: Työväentutkimus Vuosikirja
Author: Olli Pietiläinen
Language: English
Subfield: Genetics
Domain: Life Sciences
Open Access status: green
OpenAlex ID: W1539021817