New evidence of a 38-chromosomes karyotype in South American populations of the roof rat, Rattus rattus L. (Rodentia, Muridae)

Sleep disturbances in ADHD: investigating the contribution of polygenic liability for ADHD and sleep-related phenotypes

Sleep disturbances are common in attention deficit hyperactivity disorder (ADHD) and associated with poor outcomes. We tested whether, in children with ADHD, (1) polygenic liability for sleep phenotypes is over- or under-transmitted from parents, (2) this liability is linked to comorbid sleep disturbances, and (3) ADHD genetic risk is associated with comorbid sleep disturbances. We derived polygenic scores (PGS) for insomnia, chronotype, sleep duration, and ADHD, in 758 children (5-18 years old) diagnosed with ADHD and their parents. We conducted polygenic transmission disequilibrium tests for each sleep PGS in complete parent-offspring ADHD trios (N = 328) and an independent replication sample of ADHD trios (N = 844). Next, we tested whether insomnia, sleep duration, and ADHD PGS were associated with co-occurring sleep phenotypes (hypersomnia, insomnia, restless sleep, poor sleep quality, and nightmares) in children with ADHD. Children's insomnia and chronotype PGS did not differ from mid-parent average PGS but long sleep duration PGS were significantly over-transmitted to children with ADHD. This was supported by a combined analysis using the replication sample. Insomnia, sleep duration, and ADHD PGS were not associated with comorbid sleep disturbances. There is weak evidence that children with ADHD over-inherit polygenic liability for longer sleep duration and do not differentially inherit polygenic liability for insomnia or chronotype. There was insufficient evidence that childhood sleep disturbances were driven by polygenic liability for ADHD or sleep traits, suggesting that sleep disturbances in ADHD may be aetiologically different to general population sleep phenotypes and do not index greater ADHD genetic risk burden.

Mauritius type black rats with peculiar karyotypes derived from Robertsonian fission of small metacentrics

All seventeen black rats collected from Mauritius Island were characterized by having many extra small acrocentric autosomes. Their basic karyotype was of Oceanian type, because of the presence of the large metacentric M1 and M2 pairs, but chromosome numbers in 13 specimens among them were 42, those of 3 specimens 43, and those of the remaining one specimen 44. Although the Oceanian type rat had 2 small acrocentric autosomes (pair no. 13), 16 Mauritius rats had 10 small acrocentrics, and the remaining one had 8 small acrocentrics. Comparative karyotype analysis between Oceanian and Mauritius type rats showed that the extra small acrocentrics found in Mauritius rats were due to Robertsonian fission of small metacentric pairs no. 14 and 18 of the original Oceanian type rat. Only one rat with 8 small acrocentrics showed the heteromorphic pair no. 18 consisting of one metacentric and two acrocentrics. The large metacentric M1 chromosome in 13 of 17 rats examined showed homologous pair, but two of them were heteromorphic by involving one metacentric M1 and two acrocentrics. In the remaining two rats M1 chromosome was not observed, but acrocentric pairs no. 4 and 7 were included. These acrocentrics were also suggested to be originated from Robertsonian fission of the large metacentric M1 chromosome. Robertsonian fission seemed to be one of the important mechanism found in karyotype evolution.