What is the fine-grained topic of the following text: Using deep DNA-Seq data, we demonstrate by direct observations and rigorous statistical inference the existence of wide spread LHVs in human normal tissues and tumors, with higher frequencies of LHVs observed in tumor samples compared to normal, and older healthy individuals compared to younger healthy individuals. Only return the topic.
The existence and frequency of long heterogeneity variations (LHVs) in human normal tissues and tumors.