Hyperglycinemia in captive-bred vervet monkeys with cataracts: genetic dynamics and associations

Abstract

A small percentage (8%) of the captive-bred vervet monkeys (Chlorocebus aethiops) maintained at Primate Unit and Delft Animal Centre (PUDAC) of the South African Medical Research Council (SAMRC) were found to have high levels of glycine in their plasma (457- 795 ?mol/L) and cerebrospinal fluid (CSF) (7.5-12.7 ?mol/L). Additionally, these hyperglycinemic monkeys developed cataracts, a condition which has been previously characterized and reported in this specific colony of captive-bred vervet monkeys. This type of association has never been reported in literature before, therefore, this study will be the first of its kind to be investigated in non-human primates (NHPs). Nonketotic hyperglycinemia (NKH), also known as glycine encephalopathy, is well characterised in humans. The symptoms are exclusively neurological in nature, and clinically patients are diagnosed with abnormally high glycine levels in plasma (normal <350 ?mol/L) and CSF (normal range 0-8). This neurological disorder is transmitted in an autosomal recessive form and is mainly instigated by a defective glycine cleavage system (GCS). In contrast to GCS, glycine transporter (GlyT1) which regulates glycine concentration at synapses and valproate administration have been associated with NKH.