Copy number variations and risk for schizophrenia in 22q11.2 deletion syndrome

Abstract

22q11.2 Deletion Syndrome (22q11.2DS) is a common microdeletion syndrome with congenital and late-onset features. Testing for the genomic content of copy number variations (CNVs) may help elucidate the 22q11.2 deletion mechanism and the variable clinical expression of the syndrome including the high (25%) risk for schizophrenia. We used genome-wide microarrays to assess CNV content and the parental origin of 22q11.2 deletions in a cohort of 100 adults with 22q11.2DS (44 with schizophrenia) and controls. 22q11.2DS subjects with schizophrenia failed to exhibit de novo CNVs or any excess of novel inherited CNVs outside the 22q11.2 region. There were no significant effects of parental origin of the 22q11.2 deletion, deletion length, parental age or family history on expression of schizophrenia. There was no evidence for a general increase of de novo CNVs in 22q11.2DS. A novel finding was the relative paucity of males with de novo 22q11.2 deletions of paternal origin (P = 0.019). The Y chromosome may play a mediating role in the mechanism of 22q11.2 deletion events during spermatogenesis, resulting in the previously observed excess of maternal de novo 22q11.2 deletions. Hemizygosity of the 22q11.2 region appears to be the major CNV-related risk factor for schizophrenia in 22q11.2DS. The results reinforce the need for further efforts to identify specific molecular mechanisms underlying this expression and to identify the 1% of patients with schizophrenia who carry 22q11.2 deletions.

Figure 1.

22q11.2DS, copy number variants (CNVs) and parental origin of deletion. Summary of samples used for genome-wide CNV analyses and of results for analyses of parental origin of 22q11.2 deletions. Confirmed results for parental origin of deletion are based on CNV and fluorescence in situ hybridization (FISH) data for 46 trios and 19 duos. In six cases, FISH results allowed inference of a de novo (n = 5) or inherited (n = 1) 22q11.2 deletion when parental DNA was unavailable and, in five cases CNV results for siblings helped confirm parental origin. Probable results are based on CNV and FISH data for 11 duos, supplemented with clinical data for the parent whose DNA was unavailable for study.