Biallelic TRNT1 variants in a child with B cell immunodeficiency, periodic fever and developmental delay without sideroblastic anemia (SIFD variant)

Biallelic loss-of-function variants in the TRNT1 gene have been associated with a mitochondrial cytopathy impairing neuronal cell development and heme synthesis, named SIFD. The disease is commonly characterized by developmental delay and sideroblastic anemia and also panhypogammaglobulinemia. We herein report a child with two rare and functionally relevant variants in the TRTN1 gene, who had mild facial dysmorphisms, hypogammaglobulinaemia diagnosed at 6 months and a longlasting history of recurrent fevers; no sideroblastic anemia was found in this patient. The reason for the selective decrease in B cells in SIFD is not known, but hypogammaglobulinaemia may be a striking feature which heralds a more complex disorder characterized by neurologic impairment and bouts of inflammation.