Transthyretin amyloidosis (ATTR) is a protein disorder caused by the abnormal accumulation of misfolded transthyretin (TTR) protein in organs and tissues throughout the body, primarily affecting the peripheral nervous system and heart ^[1]. ATTR can be divided into hereditary ATTR and wild-type ATTR, with hereditary ATTR being caused by genetic mutations in the TTR gene.

The TTR gene encodes transthyretin (TTR), also known as prealbumin, which is mainly synthesized in the liver and to a lesser extent in the brain’s choroid plexus or ocular photoreceptor tissue (such as the retina). TTR is a transport protein that exists as a homotetramer in peripheral blood under normal physiological conditions and participates in the transport of thyroxine and retinol-binding protein. Mutations in the TTR gene can lead to hereditary familial amyloidosis, such as Transthyretin Cardiac Amyloidosis Myocardiopathy (ATTR-CM) and Transthyretin Amyloid Polyneuropathy (ATTR-PN). The pathogenic mechanism is that structurally unstable TTR protein tetramers develop into pathological aggregates in tissues such as the peripheral nervous system, heart, eyes, kidneys, and meninges, forming insoluble amyloid deposits, eventually leading to ATTR.

The treatments for ATTR-CM and ATTR-PN mainly involve inhibiting the production of mutant TTR mRNA or stabilizing the structure of TTR protein tetramers. At present, various drug pipelines have emerged in the field of gene therapy targeting the TTR gene, including ASO, siRNA, and CRISPR-based gene therapies. Among them, Inotersen Sodium, developed by Ionis, the leading oligonucleic acid drug (ASO) therapy company, is the first approved ASO drug for this disease. It targets the conserved sequence of the 3’ untranslated region (UTR) of TTR mRNA to induce mRNA degradation and reduce TTR synthesis in liver cells ^[2]. Since most ASO, siRNA, and CRISPR-based therapies target human TTR genes, considering the differences between animals and humans at the genetic level, humanizing mouse genes will help advance gene therapy drug pipelines into clinical stages. This strain is a mouse Ttr gene humanized model and can be used for research on transthyretin amyloidosis. The homozygous B6-hTTR mice are viable and fertile ^[3-6]. Additionally, based on the independently developed TurboKnockout fusion BAC recombination technology, Cyagen can also generate hot mutation models based on this strain and provide customized services for specific mutations to meet experimental needs in pharmacology.