Germ-Line and Somatic Mutations in Familial Myeloproliferative Neoplasms (MPNs). a Pilot Study

Background: Familial MPNs are uncommon disorders that, like sporadic cases, are characterized by clonal hematopoiesis and presence of somatic mutations, e.g. JAK2, CALR, MPL and occasionally TET2. There is little information, however, about germ-line mutations in these families that may explain the low penetrance hereditary predisposition.

Methods: We studied five families with MPNs, each with at least 2 affected members. After obtaining an informed consent, clinical data was obtained from the patients’ electronic medical records. Blood and buccal samples were collected from patients and unaffected relatives. Exome sequencing was performed on the blood DNA samples using Agilent SureSelect Human All Exon V5+UTRs exome capture kit followed by massively parallel sequencing with Illumina HiSeq 2000. Sanger sequencing was then done on both the blood and buccal swab DNA samples to validate selected gene variants and to differentiate the nature of those variants (germ line or somatic).

Results: The 5 families participating in this study had the following diagnoses: 1. Mother: polycythemia vera (PV); son: essential thrombocythemia (ET), 2. Mother: primary myelofibrosis (MF); daughter: unclassifiable MPN (UMPN), 3. Father: PV; son: PV, 4. Sister: MF; sister: MF, 5. Two aunts: MF; niece; UMPN. Six patients were positive for JAK2, V617F mutation. Blood and buccal samples were collected from 5 patients and 4 relatives. In all 5 families, the pro-band was younger at the time of diagnosis than his/her affected relatives. The clinical course of the MPNs appeared to be similar to the sporadic form.

Exome sequencing revealed TET2 mutations in 2 probands. In addition, novel non-synonymous mutations in several candidate genes, KMT2D, KMT2C, NBEAL1, NBEAL2, AHNAK2, RNF213, were identified in the blood samples from the patients but not their unaffected relatives. These include two novel KMT2D mutations in two unrelated families. These 2 mutations were also found in the matching buccal swab samples, indicating that they are germ line mutations.

Discussion: KMT2D and KMT2C mutations have been previously identified as somatic mutations in lymphoid malignancies, including non-Hodgkin’s lymphomas (Morin 2011), and as germ line compound heterozygote mutations in infant MLL and ALL (Valentine 2014). About 32% of diffuse large cell lymphoma and 89% of follicular lymphoma have somatic mutations of KMT2D. NBEAL2 germ line mutations are associated with familial gray platelet syndrome, where some patients have myelofibrosis (Gunay-Aygun 2011). To our knowledge, this is the first report describing germ line mutations in familial MPNs. The possible role of these mutations in predisposition to MPN will be discussed. Studies on additional families with MPNs are planned.