Comorbid Abetalipoproteinemia and Neurofibromatosis Type 1: Potential Clinical Implications of an Ultrarare Co-occurrence.

Abetalipoproteinemia (ABL) affects fewer than 1 per 1 million people, whereas neurofibromatosis type 1 (NF1) occurs in approximately 1 in 3000 to 4000 individuals. We describe the clinical findings in a 38-year-old woman with both disorders. ABL was diagnosed in the neonatal period, followed by NF1 at age 7 years based on multiple café-au-lait spots, intertriginous freckling, and Lisch nodules. Genetic testing revealed a homozygous pathogenic MTTP frameshift variant [c.215del (p.Pro72Leufs*8)] and a heterozygous pathogenic NF1 splice variant [c.205-2A>C]. To our knowledge, this co-occurrence has not been previously reported. The estimated likelihood of the co-occurrence is approximately 1 in 3 billion individuals.