Germinal heterozygous activating STAT3 mutations represent a novel monogenic defect associated with multi-organ autoimmune disease and, in some cases, severe growth retardation. By using whole-exome sequencing, we identified two novel STAT3 mutations, p.E616del and p.C426R, in two unrelated pediatric patients with IGF-I deficiency and immune dysregulation. The functional analyses showed that both variants were gain-of-function (GOF), although they were not constitutively phosphorylated. They presented differences in their dephosphorylation kinetics and transcriptional activities under interleukin-6 stimulation. Both variants increased their transcriptional activities in response to growth hormone (GH) treatment. Nonetheless, STAT5b transcriptional activity was diminished in the presence of STAT3 GOF variants, suggesting a disruptive role of STAT3 GOF variants in the GH signaling pathway. This study highlights the broad clinical spectrum of patients presenting activating STAT3 mutations and explores the underlying molecular pathway responsible for this condition, suggesting that different mutations may drive increased activity by slightly different mechanisms.

Background IGF1 is a key factor in fetal and postnatal growth. To date, only three homozygous IGF1 gene defects leading to complete or partial loss of IGF1 activity have been reported in three short patients born small for gestational age. We describe the fourth patient with severe short stature presenting a novel homozygous IGF1 gene mutation. Results We report a boy born from consanguineous parents at 40 weeks of gestational age with intrauterine growth restriction and severe postnatal growth failure. Physical examination revealed proportionate short stature, microcephaly, facial dysmorphism, bilateral sensorineural deafness and mild global developmental delay. Basal growth hormone (GH) fluctuated from 0.2 to 29 ng/mL, while IGF1 levels ranged from −1.15 to 2.95 SDS. IGFBP3 was normal-high. SNP array delimited chromosomal regions of homozygosity, including 12q23.2 where IGF1 is located. IGF1 screening by HRM revealed a homozygous missense variant NM_000618.4(IGF1):c.322T>C, p.(Tyr108His). The change of the highly conserved Tyr60 in the mature IGF1 peptide was consistently predicted as pathogenic by multiple bioinformatic tools. Tyr60 has been described to be critical for IGF1 interaction with type 1 IGF receptor (IGF1R). In vitro, HEK293T cells showed a marked reduction of IGF1R phosphorylation after stimulation with serum from the patient as compared to sera from age-matched controls. Mutant IGF1 was also less efficient in inducing cell growth. Conclusion The present report broadens the spectrum of clinical and biochemical presentation of homozygous IGF1 defects and underscores the variability these patients may present depending on the IGF/IGF1R pathway activity.

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