Somatic CALR mutations in familial myeloproliferative diseases. (A) The 3 pedigrees with somatic CALR mutations are shown in detail. Screening for CALR mutations was performed by using the sizing polymerase chain reaction (PCR) assay described by Klampfl et al.³  The JAK2-V617F mutation was screened by allele-specific PCR.⁶  Percentages in blue represent the CALR mutant allele burden. %T (red), percentage of G>T JAK2-V617F mutant allele burden; CALR+, presence of a 52-base deletion in exon 9 of the CALR gene; DN, double-negative (ie, absence of detectable mutations in CALR exon 9 and JAK2-V617F); V617F, presence of the JAK2-V617F mutation. (B) Summary of families analyzed. Affected and unaffected family members from families with familial predisposition to MPN (upper part) or HT (lower part) were screened for the presence or absence of mutations in CALR.