Fig. 2.

a) 1-DeoxySL levels in plasma samples of the patient carrying the p.S331Y mutation, family members and controls. The levels of the 1-deoxy-sphiglipids were significantly increased in the plasma of the S331Y patient but not in the plasma of the unaffected parents or unrelated healthy controls. Total sphingolipid levels were not different between patients and controls (data not shown). b) De-novo generation of sphinganine and 1-deoxy-sphinganine. HEK293 cells expressing either the S133F or S331Y mutant show a significantly reduced canonical SPT activity and a significantly increased formation of 1-deoxy-sphinganine in comparison to SPTLC1wt expressing cells. The 1-deoxy-sphinganine formation was about 30% lower for the S331Y than for the S331F mutation (**p < 0.05).