Recurrent Infections and Immunodeficiency Caused by Severe Pancytopenia Associated with a Novel Life-Threatening Mutation in Hypoxia-Upregulated Protein 1

<i>HYOU1</i> encodes a protein from the endoplasmic reticulum chaperone proteins, expressed to protect cellular mechanisms from stress such as hypoxia, insufficient energy and excessive or insufficient substances, and to restore cell homeostasis. In this study, we report a novel pathogenic variant in <i>HYOU1</i>. The proband, the second patient with pathogenic variant in <i>HYOU1</i>, was a female born to consanguineous parents. A novel homozygous pathogenic variant in <i>HYOU1</i> (NM_001130991.3: c.1456C&gt;T; p.Arg486Cys) was identified, causing anemia, thrombocytopenia and severe panleukopenia and immunodeficiency in the second month of age, leading to consistent high-grade fever, regression of brain functions and recurrent infections; ultimately resulting in the patient expiring at three and half months of age. Both parents are heterozygous for this variant and have no issues related to this study.