Human cells homozygous for rare loss-of-expression (LOE) TYK2 alleles have impaired, but not abolished, cellular responses to IFN-α/β (underlying viral diseases in the patients) and to IL-12 and IL-23 (underlying mycobacterial diseases). Cells homozygous for the common P1104A TYK2 allele have selectively impaired responses to IL-23 (underlying isolated mycobacterial disease). We report three new forms of TYK2 deficiency in six patients from five families homozygous for rare TYK2 alleles (R864C, G996R, G634E, or G1010D) or compound heterozygous for P1104A and a rare allele (A928V). All these missense alleles encode detectable proteins. The R864C and G1010D alleles are hypomorphic and loss-of-function (LOF), respectively, across signaling pathways. By contrast, hypomorphic G996R, G634E, and A928V mutations selectively impair responses to IL-23, like P1104A. Impairment of the IL-23–dependent induction of IFN-γ is the only mechanism of mycobacterial disease common to patients with complete TYK2 deficiency with or without TYK2 expression, partial TYK2 deficiency across signaling pathways, or rare or common partial TYK2 deficiency specific for IL-23 signaling.

Background: Primary immunodeficiency diseases (PID) usually presents itself with recurrent, severe, and unusual infections, along with autoimmunity and various other malignancies. But, the diversity of PID often makes the diagnosis of patients difficult for physicians other than clinical immunologists. This study aimed to describe the characteristics of patients diagnosed with PIDs during the inpatient treatment for infectious diseases, and to highlight the cases in which a PID diagnosis should be considered. Methods: The clinical, immunological, and molecular features of 81 pediatric patients treated for infectious diseases, who were diagnosed with a PID during hospitalization was retrospectively analyzed. The diagnosis was based on the PID criteria of the International Union of Immunological Societies. Results: The five main PID sub-types were identified. Predominantly, antibody deficiencies were the most common (61.7%) group. The average delay in diagnosis was 34.6 months, and the positive family history rate was 24.7%, while the consanguineous marriage rate was 45.7%. Around thirty-five (43%) patients were found to have mutated PID-related genes. While lower respiratory tract infections were the most common symptom, a fever of unknown origin was another remarkable diagnosis. Eight (9.9%) patients underwent allogeneic hematopoietic stem cell transplantation. Conclusions: Clinicians should consider a PID diagnosis, especially in the cases of recurrent, severe, or atypical infections. Increased knowledge of the alarm features of PID can promote early diagnosis.

Introduction: Thrombocytopenia is a common clinical problem in cancer patients undergoing high-dose chemotherapy and autologous hematopoietic stem cell transplantation (HSCT). It can occur as prolonged isolated thrombocytopenia (PIT) or secondary failure of platelet recovery (SFPR) and may cause potentially fatal bleeding. However, data on the treatment of post-transplant thrombocytopenia is still lacking. Methods: We reported our practices involving 15 pediatric patients who received eltrombopag (ELT) treatment for PIT and SFPR after autologous HSCT. Results: The overall response was 78.5% (11/14), with 1 patient excluded due to noncompliance. The 12 surviving patients' median follow up was 699 days (range: 167 to 2250 d). Conclusions: Our study indicates the efficacy and safety of ELT for treating PIT and SFPR after autologous HSCT in pediatric patients. However, more studies are needed to confirm these findings in children.