Via the accumulation of a signature substrate, S7P, complete TAL deficiency can be easily identified from as little as 100 μL of urine.24, 25 Although S7P does not accumulate in haplo‐insufficiency,7, 8, 24 a critical anti‐oxidant metabolite of the PPP, NADPH, is depleted in diseased tissues, such as the sperm7 and the liver.8 Due to the instability of NADPH and its lack of specificity, genetic screening offers the most reliable method of detection for partial TAL deficiency. Here, TALDO1 is linked to hyperinsulinemic hypoglycemia, familial, 4.