Homozygosity for a variant in <i>SLC10A2</i> and infancy onset severe fat‐soluble vitamin deficiency due to bile acid malabsorption

We present a case of a young female patient with persistent and severe fat-soluble vitamin deficiency since infancy. Despite extensive investigations during childhood, the underlying cause remained elusive. The patient was generally asymptomatic while receiving continuous vitamin subsidy. Exome sequencing performed at age 18 revealed a homozygous missense variant (Pro65Leu) in the gene <i>SLC10A2</i>, which encodes a bile acid transporter in the ileum. A bile retention scan showed severe bile acid malabsorption, with only 1.6% of radioactively labeled bile acids retained 7 days after intake. Treatment with a bile acid sequestrant was attempted but discontinued due to side effects and no significant effect on intestinal vitamin uptake. This case highlights the importance of early genetic testing in patients with unexplained fat-soluble vitamin deficiency. It also emphasizes the need for further research to elucidate the clinical spectrum and management of primary bile acid malabsorption due to <i>SLC10A2</i> deficiency.