Heterozygous Mutations in Both the AMN and CBS Genes: Double Haploinsufficiency as an Unusual Cause of Vitamin B12 Deficiency-A Case Report

Per Ole Iversen; Jean-Louis Gueant; Abderrahim Oussalah; Helga Refsum; Ebba Nexo; Geir E Tjønnfjord; Christian Qvigstad

doi:10.1002/ccr3.9600

Heterozygous Mutations in Both the AMN and CBS Genes: Double Haploinsufficiency as an Unusual Cause of Vitamin B₁₂ Deficiency-A Case Report

Clin Case Rep. 2024 Nov 22;12(11):e9600. doi: 10.1002/ccr3.9600. eCollection 2024 Nov.

Authors

Per Ole Iversen^{1

2}, Jean-Louis Gueant³, Abderrahim Oussalah³, Helga Refsum¹, Ebba Nexo⁴, Geir E Tjønnfjord^{2

5}, Christian Qvigstad^{2

5}

Affiliations

¹ Department of Nutrition University of Oslo Oslo Norway.
² Department of Haematology Oslo University Hospital Oslo Norway.
³ Department of Molecular Medicine, Division of Biochemistry, Molecular Biology, and Nutrition University Hospital of Nancy and INSERM UMR_S 1256, Faculty of Medicine of Nancy Nancy France.
⁴ Department of Clinical Medicine/Biochemistry Aarhus University Hospital Aarhus Denmark.
⁵ Institute of Clinical Medicine University of Oslo Oslo Norway.

Abstract

Vitamin B₁₂ deficiency is usually simple to diagnose. However, our patient demonstrates that in difficult cases, the ordinary clinician may need a transdisciplinary approach. The finding of a double haploinsufficiency as a possible cause of vitamin B₁₂ deficiency in our patient, illustrates the usefulness of performing large panel clinical exome sequencing.

Keywords: folic acid; general medicine; hematology; vitamin B12.