When the Child was Not Actin´Out: A Case Report of Inherited Actin-Related Protein 2/3 Complex Subunit 1B Deficiency

ARPC1B deficiency is a recently described rare genetic inborn error of immunity, known as actinopathies, that causes a Wiskott-Aldrich Syndrome– like (WAS-like) disease. It follows an autosomal recessive inheritance pattern, and it impairs immune synapse formation and the targeted release of lytic granules.

A 7-year-old boy from Mexico had one healthy elder maternal half-brother, born to consanguineous parents. He started showing symptoms at 6 months old, with moderate-severe atopic dermatitis. He also had bronchiolitis, allergic rhinitis, allergy to cow’s milk proteins treated with sublingual immunotherapy with allergens and a dairy-free diet with improvement, and recurrent wheezing. In time, he developed abscesses that required surgical drainage. At age 6, he was hospitalized due to periodontal abscess with infiltration into the left supraclavicular and temporal space that needed surgical drainage, Vacuum-Assisted Closure system, and antibiotic therapy for isolation of Multidrug-Resistant Klebsiella Oxytoca.
Physical examination found multiple dental cavities, cervical/ inguinal lymphadenopathy, severe extensive eczema, increased volume in the left side of the face and neck.
The immunologic workup revealed anemia, lymphocytosis, and thrombocytopenia, as well as low serum complement, total serum IgE higher than 3114 IU/mL, normal IgG, high IgA of 698.9 mg/dL, and low IgM of 31.1 mg/dL. Flow cytometry for lymphocyte subsets found CD3 lymphopenia 507 cell/ul, low CD4 311 cel/ul, and low CD8 159 cel/ul. Sequence analysis and deletion/duplication testing of the 429 genes listed in the Genes Analyzed section identified a homozygous 46-bp deletion in exon 8 of ARPC1B (c.899_944del). He received treatment with IVIG during the infectious episodes and then was switched to monthly administration, and ambulatory prophylaxis with trimethoprim-sulfamethoxazole and itraconazole.

Nowadays, few individuals have been diagnosed with the ARPC1B deficiency syndrome worldwide. Because of its recent discovery and extreme incidence, the exact mechanisms and the full spectrum of the presentation of the disease remains unknown.

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