Abstract P2-09-25: Constitutional mosaicism in hereditary cancer genes

Background: Mutations conferring cancer risk are typically inherited from one biological parent. Alternatively, a mutation may be constitutional mosaic, meaning that a fraction of cells in the body carry the mutation. This can result e.g. from a de novo mutation early in embryogenesis. Constitutional mosaicism may be an underreported cause of genetic disease [1,2] for 2 reasons: Family histories can be uninformative (mosaic mutations are typically not inherited, but can be passed on to children). Also, germline laboratory tests (if performed) are traditionally not optimized to detect low allele frequency events (in contrast to tumor tests for somatic mutations). Following our recent identification of a mosaic BRCA1 cancer patient [3], we sought to characterize additional such cases in our laboratory population.

Methods: We examined high-depth next-generation sequencing (NGS) data for pathogenic or suspected pathogenic mutations with unequal allele balance (i.e., not the expected 50-50 ratio) in blood-derived DNA. Because many factors can cause unequal allele balance in NGS, we reviewed the lab and clinical data in detail to remove cases likely due to (a) technical artifacts in NGS, (b) other somatic events, as may happen in response to chemotherapy, or (c) undiagnosed, residual or progressing blood cancers. An orthogonal assay was used for confirmation.

Results: To date, 14 cases with mosaic mutations (7-29% allele frequency) have been confirmed: 8 of these patients have breast/ovarian cancer and 6 have other cancers. These allele frequencies are unlikely to be caused by circulating tumor DNA or cells. These findings include our published BRCA1 case, 7 TP53 cases, 1 NF1 case, 2 CHEK2, 2 MLH1, and 1 PTCH1. 3 additional mutations were determined to be part of a haematopoietic neoplasm (1 previously undiagnosed). Cases of note include (i) a young breast cancer patient, with no cutaneous findings, positive for NF1 at 9%, and (ii) a patient presenting with the Muir-Torre variant of Lynch syndrome who had negative MLH1/MSH2 Sanger sequencing 14 years ago, identified to be positive for MLH1 at 25% by NGS.

Conclusion: Constitutional mosaic mutations may be an under-recognized cause of cancer and unique clinical considerations apply to such cases. First, a mosaic patient may not show the same gene-associated phenotypes as patients with inherited heterozygous mutations in the same gene. Second, patients with syndromic presentations who tested negative for the indicated gene(s) by traditional methodologies may warrant reexamination by NGS. Similarly, patients with heterozygous mutations (50-50) may have a mosaic parent, for whom the mutation could be missed by traditional testing. Testing of family members beyond first degree relatives of a mosaic patient is unlikely to modify risk assessments, unlike the situation for patients with inherited heterozygous mutations. Finally, apparent mosaicism may warrant an evaluation for a underlying haematologic malignancy. We note that the prevalence of mosaic findings in hereditary cancer genes is currently unclear but may higher than once thought. Further clinical research on this topic is clearly warranted.

(1) Campbell et al., AJHG, 2014

(2) Acuna-Hildago et al., AJHG, 2015

(3) Friedman et al., SABCS 2014; BJC 2015.

Citation Format: Lincoln S, Tan C, Kennemer M, Powers M, Monzon F. Constitutional mosaicism in hereditary cancer genes. [abstract]. In: Proceedings of the Thirty-Eighth Annual CTRC-AACR San Antonio Breast Cancer Symposium: 2015 Dec 8-12; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2016;76(4 Suppl):Abstract nr P2-09-25.

X-exome sequencing of 405 unresolved families identifies seven novel intellectual disability genes

X-linked intellectual disability (XLID) is a clinically and genetically heterogeneous disorder. During the past two decades in excess of 100 X-chromosome ID genes have been identified. Yet, a large number of families mapping to the X-chromosome remained unresolved suggesting that more XLID genes or loci are yet to be identified. Here, we have investigated 405 unresolved families with XLID. We employed massively parallel sequencing of all X-chromosome exons in the index males. The majority of these males were previously tested negative for copy number variations and for mutations in a subset of known XLID genes by Sanger sequencing. In total, 745 X-chromosomal genes were screened. After stringent filtering, a total of 1297 non-recurrent exonic variants remained for prioritization. Co-segregation analysis of potential clinically relevant changes revealed that 80 families (20%) carried pathogenic variants in established XLID genes. In 19 families, we detected likely causative protein truncating and missense variants in 7 novel and validated XLID genes (CLCN4, CNKSR2, FRMPD4, KLHL15, LAS1L, RLIM and USP27X) and potentially deleterious variants in 2 novel candidate XLID genes (CDK16 and TAF1). We show that the CLCN4 and CNKSR2 variants impair protein functions as indicated by electrophysiological studies and altered differentiation of cultured primary neurons from Clcn4(-/-) mice or after mRNA knock-down. The newly identified and candidate XLID proteins belong to pathways and networks with established roles in cognitive function and intellectual disability in particular. We suggest that systematic sequencing of all X-chromosomal genes in a cohort of patients with genetic evidence for X-chromosome locus involvement may resolve up to 58% of Fragile X-negative cases.

The effects of plasmalyte-148 vs. Hartmann's solution during major liver resection: a multicentre, double-blind, randomized controlled trial

BACKGROUND

The acid-base, biochemical and hematological effects of crystalloid solutions have not been comprehensively evaluated in patients with liver resection.

DESIGN

multicenter, prospective, double-blind randomized controlled trial investigating the biochemical effects of Hartmann's solution (HS) or Plasmalyte-148 (PL) in 60 patients undergoing major liver resection.

PRIMARY OUTCOME

base excess immediately after surgery.

SECONDARY OUTCOMES

changes in blood biochemistry and hematology.

RESULTS

At completion of surgery, patients receiving HS had equivalent mean standard base excess (-1.7±2.2 vs. -0.9±2.3 meq/L; P=0.17) to those treated with PL. However, patients treated with HS were more hyperchloremic (difference 1.7 mmol/L, 95% CI: 0.2 to 3.2, P=0.03) and hyperlactatemic (difference 0.8 mmol/L, 95% CI: 0.2 to 1.3; P=0.01). In contrast, patients receiving PL had higher mean plasma magnesium levels and lower ionized calcium levels. There were no significant differences in pH, bicarbonate, albumin and phosphate levels. Immediately after surgery, mean PT and aPTT were significantly lower in the PL group. Intraoperatively, the median (IQR) blood loss in the PL group was 300 mL (200:413) vs. 500 mL (300:638) in the HS group (P=0.03). Correspondingly, the postoperative hemoglobin was higher in the PL group. Total complications were more frequent in the HS Group (56% vs. 20%, relative risk 2.8; 95% CI: 1.3 to 6.1; P=0.007).

CONCLUSION

In liver resection patients, HS and PL led to similar base excess values but different post operative plasma biochemistry and hematology values. Understanding of these effects may help clinicians individualize fluid therapy in these patients.

Microstructured titanium regulates interleukin production by osteoblasts, an effect modulated by exogenous BMP-2

Microtextured implant surfaces increase osteoblast differentiation in vitro and enhance bone-to-implant contact in vivo and clinically. These implants may be used in combination with recombinant human bone morphogenetic protein 2 (rhBMP-2) to enhance peri-implant bone formation. However, the effect of surface modifications alone or in combination with rhBMP-2 on the osteoblast-produced inflammatory microenvironment is unknown. MG63 cells were cultured on tissue culture polystyrene or titanium substrates: smooth pretreated (PT, Ra=0.2μm), sandblasted/acid-etched (SLA, Ra=3.2μm) or hydrophilic-SLA (modSLA). Expression and protein production of pro-inflammatory interleukins (IL1b, IL6, IL8, IL17) and anti-inflammatory interleukins (IL10) were measured in cells with or without rhBMP-2. To determine which BMP signaling pathways were involved, cultures were incubated with BMP pathway inhibitors to blockSmad (dorsomorphin), TAB/TAK1 ((5Z)-7-oxozeaenol) or PKA (H-8) signaling. Culture on rough SLA and modSLA surfaces decreased pro-inflammatory interleukins and increased anti-inflammatory IL10. This effect was negated in cells treated with rhBMP-2, which caused an increase in pro-inflammatory interleukins and a decrease in anti-inflammatory interleukins through TAB/TAK signaling. The results suggest that surface microtexture modulates the inflammatory process during osseointegration, an effect that may enhance healing. However, rhBMP-2 in combination with microtextured titanium implants can influence the effect of cells on these surfaces, and may adversely affect cells involved in osseointegration.

A clinical analysis of 58 chinese cases of pigmented fungiform papillae of the tongue

BACKGROUND

Pigmented fungiform papillae of the tongue (PFPT) is a disorder in which the fungiform papillae of the tongue have abnormal coloration. However, Chinese-specific clinical data for PFPT are lacking.

OBJECTIVE

To determine the prevalence and characteristics of PFPT among the Chinese population.

METHODS

A survey was carried out using a clinical examination and a questionnaire on 14,346 first-time outpatients in our dermatology department, and 58 cases of PFPT were subsequently diagnosed.

RESULTS

The prevalence of PFPT was 0.4% among dermatological outpatients. All patients had pin-sized, brownish fungiform papillae on the tip, lateral or dorsal parts of the tongue. Of the three subtypes, type I was the most common (87.93%). PFPT generally coexisted with Hori's nevus (48.28%), melasma (20.69%), hysteromyoma (24.14%) and breast cystic hyperplasia (20.69%).

CONCLUSION

Our study confirms that PFPT is a relatively common disorder among Chinese outpatients, and it was presumed to be closely coupled with Hori's nevus, melasma and other disorders.

Adipocytokine zinc α2 glycoprotein (ZAG) as a novel urinary biomarker for normo-albuminuric diabetic nephropathy

OBJECTIVE

A substantial proportion of diabetic nephropathy individuals are non-albuminuric. Using a proteomic approach, we searched for novel urinary biomarkers.

METHODS

We studied three groups (n = 6 per group) of males with Type 2 diabetes: (1) normal renal function; (2) classical diabetic nephropathy (urinary albumin-creatinine ratio > 1000 mg/g and glomerular filtration rate < 60 ml/min.1.73 m(2) ) and (3) non-albuminuric diabetic nephropathy (glomerular filtration rate < 60 ml/min.1.73 m(2) and urinary albumin-creatinine ratio < 30 mg/g). We used two-dimensional fluorescence differential gel electrophoresis, matrix-assisted laser desorption/ionization time-of-flight mass spectrometry peptide identification and western blot validation in the study.

RESULTS

Sixty protein spots were differentially abundant between the non-albuminuric and macro-albuminuric subjects (> 2.5-fold, P < 0.05). In the non-albuminuric subjects, in addition to previously reported α(1) -microglobulin, the next most interesting spot (upregulated 3.44-fold, P = 0.0026) was human zinc-α(2) -glycoprotein, a novel adipose-cytokine associated with glomerular injury. This was confirmed by western blot and replicated in female diabetic nephropathy subjects.

CONCLUSIONS

From our preliminary results, human zinc-α(2) -glycoprotein may be a novel urinary biomarker for non-albuminuric diabetic nephropathy.