Sphingolipids are a collection of membrane-bound lipids and bioactive signalling molecules that modulate fundamental cell functions. Central to the sphingolipid pathway, Dihydroceramide desaturase (Des1) inserts a double bond into its substrate to generate ceramide, a precursor to sphingomyelin, glycosphingolipids and bioactive signalling molecules sphingosine and sphingosine 1-phosphate. The enzyme activity of Des1 thus controls the saturation of the cellular sphingolipidome and a loss of Des1 leads to the accumulation of dihydrosphingolipids. The balance of saturated (dihydro) and unsaturated sphingolipids can broadly alter cellular membrane dynamics and impact on cell growth, proliferation and stress responses. Alterations in Des1 activity via inhibition or knockout have implicated the loss of Des1 activity with changes in neuronal function, haematopoiesis, cardiovascular function and metabolism. Here we discuss the enzymatic function of Des1 and investigate a panel of Des1 missense patient mutations for their impact on enzyme activity. Our findings suggest a correlation between the proportion of Des1 activity and disease severity in patients with hypomyelinating leukodystrophy.