The importance of defining the age-specific TREC/KREC levels for detection of various inborn errors of immunity in pediatric and adult patients.

This study aimed to establish physiological TREC/KREC values in a healthy population of different ages to create cut-offs and analyze pediatric patients with various inborn errors of immunity. Dry blood spots and DNA samples purified from whole blood were used for TREC/KREC quantification using real-time PCR. Observed difference (p < 0.001) between methods revealed the isolation method as a factor we need to consider when determinating cut-offs. Data of 713 healthy individuals showed a negative correlation (p < 0.001) between age and TREC/KREC levels with gender difference observed only for KREC in a group of 51-60 years old (p < 0.001). The 5th percentile cut-off values were set for age groups, which allowed us to identify 25% of patients with immunodeficiencies in case of non-zero, borderline values of TREC/KREC. Screening of infants with congenital heart disease identified 11% of patients with lowered TREC/KREC and shows potential for newborn screening of specific groups of patients.

Clinical evolution, genetic landscape and trajectories of clonal hematopoiesis in SAMD9/SAMD9L syndromes.

Germline SAMD9 and SAMD9L mutations (SAMD9/9Lmut) predispose to myelodysplastic syndromes (MDS) with propensity for somatic rescue. In this study, we investigated a clinically annotated pediatric MDS cohort (n = 669) to define the prevalence, genetic landscape, phenotype, therapy outcome and clonal architecture of SAMD9/9L syndromes. In consecutively diagnosed MDS, germline SAMD9/9Lmut accounted for 8% and were mutually exclusive with GATA2 mutations present in 7% of the cohort. Among SAMD9/9Lmut cases, refractory cytopenia was the most prevalent MDS subtype (90%); acquired monosomy 7 was present in 38%; constitutional abnormalities were noted in 57%; and immune dysfunction was present in 28%. The clinical outcome was independent of germline mutations. In total, 67 patients had 58 distinct germline SAMD9/9Lmut clustering to protein middle regions. Despite inconclusive in silico prediction, 94% of SAMD9/9Lmut suppressed HEK293 cell growth, and mutations expressed in CD34+ cells induced overt cell death. Furthermore, we found that 61% of SAMD9/9Lmut patients underwent somatic genetic rescue (SGR) resulting in clonal hematopoiesis, of which 95% was maladaptive (monosomy 7 ± cancer mutations), and 51% had adaptive nature (revertant UPD7q, somatic SAMD9/9Lmut). Finally, bone marrow single-cell DNA sequencing revealed multiple competing SGR events in individual patients. Our findings demonstrate that SGR is common in SAMD9/9Lmut MDS and exemplify the exceptional plasticity of hematopoiesis in children.