Congenital analbuminemia

Plasma oncotic pressure is important to prevent edema, right? And you would think that albumin, which plays a critical role in the binding of multiple plasma proteins and ionized calcium, is essential to life, right?

The rare, autosomal recessive disorder congenital analbuminemia would seem to suggest otherwise. Although it is extremely rare (estimated at less than one in a million), it is able to teach us important physiologic lessons. The disease is caused by mutations in the human serum albumin (HSA) gene which result in a markedly decreased serum albumin concentration (estimated at between 1/100th to 1/1000th of the normal serum albumin concentration), individuals with the disorder generally do well, usually with only mild edema that may even go unrecognized in childhood. Individuals do not have proteinuria but often have hyperlipidemia. It is postulated that oncotic pressure is maintained in part by an increased hepatic synthesis of other plasma proteins to compensate.

The generally mild phenotype is fairly surprising in my opinion because of the many physiologic roles ascribed to albumin in biology. It also hints that perhaps something other than the hypoalbuminemia and subsequent loss of oncotic pressure observed in patients with nephrotic syndrome is responsible for their edema.