Macular Telangiectasia Type II (MacTel) is a moderately rare eye disorder (prevalence ~1/1000) that has a suspected genetic basis. First described in the early 1980s it remains difficult to diagnose with few early onset signs. Small families are observed, but with incomplete penetrance. Its genetic risk factors remained a mystery until in 2017 we performed the first genome-wide association study (GWAS) for this retinal disorder. Despite the modest size of the GWAS (~500 patients) we replicated four loci, three of which were implicated in the glycine/serine, one-carbon metabolic pathway. This talk will detail the follow up work from the GWAS which has recently identified Mendelian forms of the disorder, including a link to a Mendelian neuropathy. Extensive metabolomic analysis on patient cohorts and mendelian randomisation studies, utilizing a large-scale GWAS of metabolites in >50K individuals, have also helped to pinpoint the dysregulation to the glycine/serine pathway. The retina is an understudied tissue and is not present in GTEX. Despite this we have been able to identify several highly plausible causal genes from the GWAS.