Polyploidy (or whole-genome duplication) is the condition of having more than two basic sets of chromosomes. Polyploidization is well tolerated in many species and can lead to specific biological functions. In mammals, programmed polyploidization takes place during development in certain tissues, such as the heart and placenta, and is considered a feature of differentiation. However, unscheduled polyploidization can cause genomic instability and has been observed in pathological conditions, such as cancer. Polyploidy of the liver parenchyma was first described more than 100 years ago. The liver is one of the few mammalian organs that display changes in polyploidy during homeostasis, regeneration and in response to damage. In the human liver, approximately 30% of hepatocytes are polyploid. The polyploidy of hepatocytes results from both nuclear polyploidy (an increase in the amount of DNA per nucleus) and cellular polyploidy (an increase in the number of nuclei per cell). In this Review, we discuss the regulation of polyploidy in liver development and pathophysiology. We also provide an overview of current knowledge about the mechanisms of hepatocyte polyploidization, its biological importance and the fate of polyploid hepatocytes during liver tumorigenesis.

多倍体（或全基因组重复）是具有两个以上基本染色体组的条件。多倍体化在许多物种中得到很好的耐受，并且可以导致特定的生物学功能。在哺乳动物中，程序化多倍体化发生在某些组织（例如心脏和胎盘）的发育过程中，被认为是分化的特征。但是，计划外的多倍体化可能会导致基因组不稳定，并且已在诸如癌症等病理状况中观察到。肝实质的多倍性最早是在100多年前描述的。肝脏是为数不多的在稳态，再生和响应损伤过程中显示多倍性变化的哺乳动物器官之一。在人类肝脏中，大约30％的肝细胞是多倍体。肝细胞的多倍性来自核多倍性（每个核的DNA量增加）和细胞多倍性（每个细胞的核数增加）。在这篇综述中，我们讨论了肝脏发育和病理生理学中多倍体的调控。我们还提供了有关肝细胞多倍化机制，其生物学重要性以及肝肿瘤发生过程中多倍体肝细胞命运的最新知识的概述。