Increased Frequency of Clonal Hematopoiesis of Indeterminate Potential in Bloom Syndrome Probands and Carriers

Background

Bloom Syndrome (BSyn) is an autosomal recessive disorder caused by biallelic germline variants in BLM, which functions to maintain genomic stability. BSyn patients have poor growth, immune defects, insulin resistance, and a significantly increased risk of malignancies, most commonly hematologic. The malignancy risk in carriers of pathogenic variants in BLM (BLM variant carriers) remains understudied. Clonal hematopoiesis of indeterminate potential (CHIP) is defined by presence of somatic mutations in leukemia-related genes in blood of individuals without leukemia and is associated with increased risk of leukemia. We hypothesize that somatic mutations driving clonal expansion may be an underlying mechanism leading to increased cancer risk in BSyn patients and BLM variant carriers.

Methods

To determine whether de novo or somatic variation is increased in BSyn patients or carriers, we performed and analyzed exome sequencing on BSyn and control trios.

Results

We discovered that both BSyn patients and carriers had increased numbers of low-frequency, putative somatic variants in CHIP genes compared to controls. Furthermore, BLM variant carriers had increased numbers of somatic variants in DNA methylation genes compared to controls. There was no statistical difference in the numbers of de novo variants in BSyn probands compared to control probands.

Conclusion

Our findings of increased CHIP in BSyn probands and carriers suggest that one or two germline pathogenic variants in BLM could be sufficient to increase the risk of clonal hematopoiesis. These findings warrant further studies in larger cohorts to determine the significance of CHIP as a potential biomarker of aging, cancer, cardiovascular disease, morbidity and mortality.

Novel association of familial testicular germ cell tumor and autosomal dominant polycystic kidney disease with PKD1 mutation

Adolescent brothers were diagnosed with testicular germ cell tumors within the same month. Both were found to have multiple renal cysts on pretreatment imaging done for staging. The proband, his brother, and their mother, were all found to have a novel splice variant in intron 8 of the PKD1 gene by clinical exome sequencing. This is the second family reported with both familial testicular germ cell tumor (FTGCT) and autosomal dominant polycystic kidney disease (ADPKD), and the first described association of FTGCT with a splice variant in PKD1. We suggest that this novel variant in PKD1 may convey increased risk for FTGCT in addition to causing ADPKD.

Dry eye-induced conjunctival epithelial squamous metaplasia is modulated by interferon-gamma

PURPOSE

To investigate the role of interferon (IFN)-gamma in the pathogenesis of conjunctival squamous metaplasia in dry eye.

METHODS

Experimental dry eye was created by subjecting C57BL/6 and IFN-gamma-knockout mice to desiccating environmental stress for 5 or 10 days. T-cell antigens and IFN-gamma were detected by immunohistochemistry. Goblet cells were counted in periodic acid Schiff (PAS)-stained sections. Expression of small, proline-rich protein (SPRR)-2 was evaluated by confocal microscopy. Tear IFN-gamma was measured by immunobead assay.

RESULTS

Dry eye promoted migration of CD4+ T cells and IFN-gamma+ cells into goblet cell zones of the conjunctiva and increased the concentration of IFN-gamma in tears. This migration was accompanied by progressive goblet cell loss and an increase in SPRR-2 expression in the conjunctival epithelium. A significant inverse correlation was observed between the density of infiltrating CD4+ T cells and goblet cells. Dry eye had no effect on conjunctival goblet cell density in IFN-gamma-knockout mice; however, exogenous administration of IFN-gamma significantly decreased goblet cell density after 5 days.

CONCLUSIONS

Conjunctival epithelial response to experimental dryness is related to the degree of CD4+ T-cell infiltration and the level of IFN-gamma production. These findings suggest that IFN-gamma plays a pivotal role in promoting conjunctival squamous metaplasia in dry eye, and they provide insight into the immune pathogenesis of keratoconjunctivitis sicca.

Experience-dependent modulation of motor corticospinal excitability during action observation

The primate premotor cortex is endowed with an "action observation/execution matching system", that is, the same premotor neurons discharge when actions are performed and when actions are observed. Hence, this system predicts a strong visual input to the motor system. Whether this input is dependent on visual experience or not has not been previously investigated. To address this issue we compared corticospinal excitability while subjects viewed frequently observed and less frequently observed hand actions of others and of themselves. Motor corticospinal excitability was larger when the action orientations were as they are frequently observed (Self-away, subject's own hand facing out from the subject, or Other-toward, an unknown hand facing toward the subject) compared with less frequently observed actions (Self-toward, subject's own hand facing "toward" the subject, or Other-away, an unknown hand facing out from the subject). This finding suggests that the modulation of motor corticospinal excitability during action observation and hence the "action observation/execution matching system" is largely dependent upon visual experience.