Homocarnosinosis, an elevation of homocarnosine, is a biochemical aberration of unknown significance. Only one such family has been reported (Sjaastad et al., 2018). Homocarnosinosis was previously thought to be a disorder characterized by marked elevation of homocarnosine in the cerebrospinal fluid along with spastic paraplegia, impaired intellectual development, and retinal pigmentation based on the report of one Norwegian family reported by Sjaastad et al. (1976). Sjaastad et al. (2018) performed genetic analysis postmortem in this family and identified a homozygous mutation in the SPG11 gene (610844). A reevaluation of the clinical symptoms and findings in the family correlated with spastic paraplegia-11 (SPG11; 604360). A study of other patients with SPG11 did not find elevated levels of homocarnosine.

A rare inborn error of metabolism characterized by low serum carnosinase activity, persistent carnosinuria, and carnosinemia. The clinical phenotype is highly variable, with some patients remaining asymptomatic, while others have been reported to show severe developmental delay, intellectual disability, hypotonia, seizures, and other neurological signs and symptoms.