May regulate the number of excitatory synapses that are formed on hippocampus neurons. Has no effect on inhibitory synapses. Forms homotrimers which can further assemble to form higher-order oligomeric complexes. Interacts with ADGRB3. May interact with ERFE. Forms heterooligomers with C1QL3 and C1QL4, when proteins are coexpressed; this interaction does not occur after secretion. Highest expression in eye, followed by placenta and brain, intermediate expression in adipose tissue and lowest expression in lymph node and testis. Glycosylated, but not with N-linked glycans.