SIDS infants have reduced 5-HT in the raphe obscurus (ROb) and the nucleus paragigantocellularis lateralis (PGCL), two medullary 5-HT source nuclei (i.e. those nuclei containing serotonergic neuronal cell bodies) that release 5-HT through projections to target nuclei (i.e. those nuclei containing 5-HT receptors but not serotonergic cell bodies) (28). Here, HTR5A is linked to sudden infant death syndrome.