Quantitation of Repetitive Sequences in Human Genomic DNA and Detection of an Elevated Ribosomal Repeat Copy Number in Schizophrenia: The Results of Molecular and Cytogenetic Analyses

A modified version of quantitating repetitive sequences in genomic DNA was developed to allow comparisons for numerous individual genomes and simultaneous analysis of several sequences in each DNA specimen. The relative genomic content of ribosomal repeats (rDNA) was estimated for 75 individuals, including 33 healthy donors (HD) and 42 schizophrenic patients (SP). The rDNA copy number in HD was 427 ± 18 (mean ± SE) per diploid nucleus, ranging 250–600. In SP, the rDNA copy number was 494 ± 15 and ranged 280–670, being significantly higher than in HD. The two samples did not differ in contents of sequences hybridizing with probes directed to a subfraction of human satellite III or to the histone genes. Cytogenetic analysis (silver staining of metaphase chromosomes) showed that the content of active rRNA genes in nucleolus organizer regions is higher in SP compared with HD. The possible causes of the elevated rRNA gene dosage in SP were considered. The method employed was proposed for studying the polymorphism for genomic content of various repeats in higher organisms, including humans.