David Herman MacLennan OC OOnt FRS FRSC (July 3, 1937 - June 24, 2020) was a Canadian biochemist and geneticist known for his basic work on proteins that regulate calcium flux through the sarcoplasmic reticulum (SR), thereby regulating muscle contraction and relaxation, and for his discoveries in the field of muscle diseases caused by genetic defects in calcium regulatory proteins.

[1] Born in Swan River, Manitoba, to Douglas MacLennan and Sigriður Sigurðardóttir, he received a BSA from the University of Manitoba in 1959 and a DSc (hc) in 2001.

[2] He received MS (1961) and PhD (1963) degrees from Purdue University under Harry Beevers, and was then a postdoctoral fellow (1963–1964) under David E. Green and an assistant professor (1964–1968) at the University of Wisconsin–Madison.

He led teams that defined the genetic basis for the human skeletal muscle diseases, malignant hyperthermia, central core disease and Brody disease and was part of the team that demonstrated that mutations in phospholamban, a regulator of the calcium pump, can cause cardiomyopathy.

[4] His identification of a calcium release channel mutation that causes porcine stress syndrome resulted in a diagnostic test that has decreased the incidence of the disease dramatically, with substantial economic benefits to the swine industry.