A Prospective Study and Identification of Genomewide Association Markers of Familial Predisposition to Plasma Cell Dyscrasias

Introduction: An increased inherited risk for the development of plasma cell dyscrasias (PCDs) has long been suspected, however to date, only a limited number of potential genomic risk loci have been described. To characterize the inherited risk and facilitate identification of additional risk loci it is important to combine detailed pedigrees with extensive genetic analysis. To identify familial PCDs we initiated a prospective study with active recruitment of a large cohort of patients with PCDs and active screening of their relatives combined with tissue banking and subsequent genetic analysis.

Methods: All patients in the Department of Clinical Therapeutics diagnosed with PCDs between January 2017 and January 2019, were offered enrollment in the study. Following informed consent, 1^st and 2^nd degree relatives over the age of 30 were eligible for screening. A detailed family pedigree was created for each index case with special focus on family history of PCDs, B-cell lymphomas, or other hematologic or solid malignancies. As a control, subjects' spouses were also screened. Screening included serum protein electrophoresis with immunofixation. In families where an additional member was identified with a PCD or B-cell malignancy, peripheral blood was collected from consenting family members over the age of 18 for further genetic analysis. Samples from affected individuals were profiled using whole genome sequencing (WGS) and unaffected individuals were genotyped using Axiom Arrays. Data were analyzed using Axion Array Suite and plink and GATK toolkit with BWA.

Results: Of 1,084 patients screened for participation in the study; 752 had multiple myeloma (MM), 77 had smoldering MM, 81 a monoclonal gammopathy of undetermined significance, 93 Waldenström's Macroglobulinemia and 81 had AL amyloidosis. 176 (16.2%) patients refused to participate in the study, while 44 (4.1%) patients were ineligible for further screening due to the absence of a living first- or second-degree relative. The median number of screened first or second-degree relatives per index patient was 3 (range 1 to 10). The median age of index cases was 65 years, offspring was 37 years, second-degree relatives was 65 years, and spouses was 65 years. The incidence of a PCD among second-degree relatives was 4.5%, while it was 0.6% among offspring. As a control group, the incidence of PCDs among spouses was 2.6%.

Overall at least one additional member (beyond the index patient) with a monoclonal gammopathy was detected in 98 families (11.3%). In 57 families (6.6%) there was a positive history of at least one additional first- or second-degree relative with a PCD or B-cell malignancy. In addition, 41 new cases of monoclonal gammopathy (4.7%) were identified through the screening process associated with this study.

To identify genetic loci that could be associated with a predisposition to development of PCDs, genetic analysis was performed on the most heavily affected 18 families, those with at least three affected members or with early onset disease (i.e. PCD diagnosed before age 50). We have evaluated 838,750 SNPs from 103 samples from 18 families. 30 samples were from affected members and 73 from unaffected members. We found eight SNPs (rs13233413, rs11648113, rs59444635, rs148480125, rs113556240, rs11547122, rs671880, rs4726610) that are significantly enriched in affected members with a p-value below the suggestive cut-off of <1e-5. The top candidate was in the untranslated region (UTR) of TSPAN33, a marker of activated and malignant B-cells. We did not detect any significant enrichment in germline mutations in previously reported genes associated with familial PCD risk such as KDM1a, KRAS or DIS3. Functional annotation of the 8 SNPs identified here showed that rs148480125, located in the promoter region of the apoptosis regulator SIVA1, is predicted to impact the allele specific expression level. Further validation work is ongoing.

Conclusions: Our active prospective screening approach to identify familial predisposition to PCDs revealed that 11.3% of patients had families with at least one additional affected member and some families had a substantially higher incidence of PCDs with earlier onset. Study of these high-risk families have identified genomewide association markers which in future may help us define familial predisposition to plasma cell dyscrasias.