It is a large (155 kilodaltons), soluble glycoprotein that circulates in human plasma (at typical concentrations of 200–300 micrograms per milliliter[5][6][7]).

[10] The lower activity conformation is the predominant form in solution and is sufficient to control fluid phase amplification.

Overactive factor H may result in reduced complement activity on pathogenic cells – increasing susceptibility to microbial infections.

It is not surprising, therefore, that rare mutations or common single nucleotide polymorphisms (SNPs) in the complement factor H gene (CFH) often result in pathologies.

In 2005, several independent research groups identified an SNP in CFH, which results in the protein change p.Y402H, as a risk factor for Age Related Macular Degeneration (AMD) present in around a third of Europeans.

[30] The British complementologist, Simon J. Clark demonstrated that FHL-1 was the predominant form of FH protecting Bruch's membrane[31], an integral part of the outer Blood-retinal barrier and a major site of early AMD.

It can be either acquired (e.g. following infection with shigatoxigenic Escherichia coli), or inherited (also known as atypical hemolytic uremic syndrome, aHUS).

aHUS has been strongly linked to mutations in genes of the complement system, especially factor H.[30] In contrast to AMD and C3 glomerulopathy (another complement-mediated renal disorder) which are mainly associated with variation in the N-terminus (CCPs 1 to 4), predisposing mutations in factor H mainly affect the C-terminus of the protein (CCP modules 19 and 20),[30] which has been shown to be responsible for adherence to renal tissues and the regulation of complement components and their downstream effectors.

[30][41][42] Biologically active Factor H has been produced by Ralf Reski and coworkers in the moss bioreactor,[43] in a process called molecular farming.

[44] Gemini Therapeutics Inc. was a Massachusetts based precision medicine company focused on the development of new therapies through a deeper understanding of disease.