Which fatty acid disorder might present with severe hypoglycemia and low ketones?

The correct answer is Medium Chain Acyl-CoA Dehydrogenase Deficiency (MCADD), which is a fatty acid oxidation disorder. MCADD is characterized by the inability to oxidize medium-chain fatty acids effectively. In individuals with MCADD, particularly during periods of fasting or illness, the body cannot mobilize fatty acids for energy, which leads to a reliance on carbohydrates that may become depleted, resulting in severe hypoglycemia.

In this condition, low levels of ketones are also observed because, due to the impaired fatty acid oxidation, there are insufficient fatty acids being converted to ketones for energy during times of fasting.

The other disorders listed—LCHADD, VLCADD, and SCADD—are associated with longer-chain fatty acids and result in different metabolic profiles. They may show different biochemical presentations including elevated ketones or different forms of hypoglycemia depending on the particular chain length of the fatty acids they cannot metabolize. In general, they do not present with the same severe hypoglycemia and low ketones characteristic of MCADD, which is why this disorder stands out in this context.