The JAK2 46/1 haplotype does not predispose to CALR-mutated myeloproliferative neoplasms.

Somatic mutations in the CALR gene were recently discovered in a substantial proportion of Philadelphia-negative chronic myeloproliferative neoplasm (cMPN) patients lacking JAK2 and MPL mutations. Somatically acquired defects are not the only pathogenic mechanism involved in these disorders. Since germline JAK2 46/1 haplotype predisposes to cMPN-associated mutations, including JAK2V617F and MPLW515K7L, we evaluated whether the 46/1 haplotype also confers susceptibility to CALR-mutated cMPN, both in sporadic and familial cases. The single-nucleotide polymorphism rs10974944, which tags 46/1, was investigated in 155 sporadic MPN patients and 270 unrelated controls, as well as in 11 familial cMPN cases and 36 unaffected relative controls. As described elsewhere, the 46/1 haplotype was overrepresented, both in sporadic and familial cMPN. In sporadic cMPN, the JAK2 46/1 haplotype was closely associated with JAK2V617F (p = 0.0003) but not with JAK2-nonmutated cases. Analysis of CALR-mutated sporadic cMPN (n = 22) showed no association between CALR mutations and 46/1 haplotype (p = 0.87). Regarding the familial cMPN, the prevalence of carriers of the G allele was higher in familial (81.8%) than in sporadic (62%) cMPN, but it did not differ significantly (p = 0.3). Although we described a family with carriers of both JAK2V617F and CALR mutations, due to the low number of CALR-mutated familial cases, we could not determinate whether the JAK2 46/1 haplotype predisposes or does not to CALR-mutated familial cMPN. We conclude, for the first time, that the 46/1 haplotype, unlike JAK2V617F and MPLW515K7L, is not associated with CALR-mutated cMPN.

A missense mutation in gamma-glutamyl carboxylase gene causes combined deficiency of all vitamin K-dependent blood coagulation factors.

To identify potential mutations in the gamma-glutamyl carboxylase gene, the sequence of all exons and intron/exon borders was determined in 4 patients from a consanguineous kindred with combined deficiency of all vitamin K-dependent procoagulants and anticoagulants and results were compared with normal genomic sequence. All 4 patients were homozygous for a point mutation in exon 9 that resulted in the conversion of an arginine codon (CTG) to leucine codon (CGG) at residue 394. Screening of this mutation based on introduction of Alu I site in amplified fragment from normal allele but not from the mutated allele showed that 13 asymptomatic members of the kindred were heterozygous for the mutation. The mutation was not found in 340 unrelated normal chromosomes. The segregation pattern of the mutation which is the first reported in the gamma-glutamyl carboxylase gene fits perfectly with phenotype of the disorder and confirms the suggested autosomal recessive pattern of inheritance of combined deficiency of all vitamin K-dependent procoagulants and anticoagulants in this kindred. The mutated carboxylase protein expressed in Drosophila cells was stable but demonstrated threefold reduced activity compared with WT carboxylase, confirming that the L394R mutation results in a defective carboxylase.

Genomic sequence and transcription start site for the human gamma-glutamyl carboxylase.

The human gene for gamma-glutamyl carboxylase is 13 kb in length and contains 15 exons. Transcription starts at a cytosine 217 base pair upstream of the first codon. There are two major transcripts in all tissues examined. They are distinguished by the presence of an Alu sequence in the 3' nontranslated end of the longer species. Relative mRNA levels for 12 bovine tissues are presented.