Lack of MEF2A Δ7aa mutation in Irish families with early onset ischaemic heart disease, a family based study

Background: Ischaemic heart disease (IHD) is a complex disease due to the combination of environmental and genetic factors. Mutations in the MEF2A gene have recently been reported in patients with IHD. In particular, a 21 base pair deletion (Δ7aa) in the MEF2A gene was identified in a family with an autosomal dominant pattern of inheritance of IHD. We investigated this region of the MEF2A gene using an Irish family-based study, where affected individuals had early-onset IHD. Methods: A total of 1494 individuals from 580 families were included (800 discordant sib-pairs and 64 parent-child trios). The Δ7aa region of the MEF2A gene was investigated based on amplicon size. Results: The Δ7aa mutation was not detected in any individual. Variation in the number of CAG (glutamate) and CCG (proline) residues was detected in a nearby region. However, this was not found to be associated with IHD. Conclusion: The Δ7aa mutation was not detected in any individual within the study population and is unlikely to play a significant role in the development of IHD in Ireland. Using family-based tests of association the number of tri-nucleotide repeats in a nearby region of the MEF2A gene was not associated with IHD in our study group. © 2006 Horan et al; licensee BioMed Central Ltd.

CRYBB1 mutation associated with congenital cataract and microcornea

The molecular characterization of a UK family with an autosomal dominant congenital cataract associated with microcornea is reported. METHODS: Family history and clinical data were recorded. This phenotype was linked to a 7.6 cM region of chromosome 22q11.2-q12.2, spanning the beta-crystallin gene cluster (ZMax of 3.91 for marker D22S1114 at theta=0). Candidate genes were PCR amplified and screened for mutations on both strands using direct sequencing. RESULTS: Sequencing of the coding regions and flanking intronic sequences of CRYBB2 and CRYBB1 showed the presence of a novel, heterozygous X253R change in exon 6 of CRYBB1. SSCP analysis confirmed that this sequence change segregated with the disease phenotype in all available family members and was not found in 109 ethnically matched controls. CONCLUSIONS: X253R is predicted to elongate the COOH-terminal extension of the protein and would be expected to disrupt beta-crystallin interactions. This is the first documented involvement of CRYBB1 in ocular development beyond cataractogenesis.

JAK2 exon 12 mutations in polycythemia vera and idiopathic erythrocytosis

Background The V617F mutation, which causes the substitution of phenylalanine for valine at position 617 of the Janus kinase (JAK) 2 gene (JAK2), is often present in patients with polycythemia vera, essential thrombocythemia, and idiopathic myelofibrosis. However, the molecular basis of these myeloproliferative disorders in patients without the V617F mutation is unclear. Methods We searched for new mutations in members of the JAK and signal transducer and activator of transcription (STAT) gene families in patients with V617F-negative polycythemia vera or idiopathic erythrocytosis. The mutations were characterized biochemically and in a murine model of bone marrow transplantation. Results We identified four somatic gain-of-function mutations affecting JAK2 exon 12 in 10 V617F-negative patients. Those with a JAK2 exon 12 mutation presented with an isolated erythrocytosis and distinctive bone marrow morphology, and several also had reduced serum erythropoietin levels. Erythroid colonies could be grown from their blood samples in the absence of exogenous erythropoietin. All such erythroid colonies were heterozygous for the mutation, whereas colonies homozygous for the mutation occur in most patients with V617F-positive polycythemia vera. BaF3 cells expressing the murine erythropoietin receptor and also carrying exon 12 mutations could proliferate without added interleukin-3. They also exhibited increased phosphorylation of JAK2 and extracellular regulated kinase 1 and 2, as compared with cells transduced by wild-type JAK2 or V617F JAK2. Three of the exon 12 mutations included a substitution of leucine for lysine at position 539 of JAK2. This mutation resulted in a myeloproliferative phenotype, including erythrocytosis, in a murine model of retroviral bone marrow transplantation. Conclusions JAK2 exon 12 mutations define a distinctive myeloproliferative syndrome that affects patients who currently receive a diagnosis of polycythemia vera or idiopathic erythrocytosis.

The myeloproliferative disorder-associated JAK2 V617F mutant escapes negative regulation by suppressor of cytokine signaling 3

The somatic JAK2 valine-to-phenylalanine (V617F) mutation has been detected in up to 90% of patients with polycythemia and in a sizeable proportion of patients with other myeloproliferative disorders such as essential thrombocythemia and idiopathic myelofibrosis. Suppressor of cytokine signaling 3 (SOCS3) is known to be a strong negative regulator of erythropoietin (EPO) signaling through interaction with both the EPO receptor (EPOR) and JAK2. We report here that JAK2 V617F cannot be regulated and that its activation is actually potentiated in the presence of SOCS3. Instead of acting as a suppressor, SOCS3 enhanced the proliferation of cells expressing both JAK2 V617F and EPOR. Additionally, although SOCS1 and SOCS2 are degraded in the presence of JAK2 V617F, turnover of SOCS3 is inhibited by the JAK2 mutant kinase and this correlated with marked tyrosine phosphorylation of SOCS3 protein. We also observed constitutive tyrosine phosphorylation of SOCS3 in peripheral blood mononuclear cells (PBMCs) derived from patients homozygous for the JAK2 V617F mutant. These findings suggest that the JAK2 V617F has overcome normal SOCS regulation by hyperphosphorylating SOCS3, rendering it unable to inhibit the mutant kinase. Thus, JAK2 V617F may even exploit SOCS3 to potentiate its myeloproliferative capacity.

Intragenic SNP haplotypes associated with 84dup18 mutation in TNFRSF11A in four FEO pedigrees suggest three independent origins for this mutation.

Familial expansile osteolysis (FEO) is a rare disorder causing bone dysplasia. The clinical features of FEO include early-onset hearing loss, tooth destruction, and progressive lytic expansion within limb bones causing pain, fracture, and deformity. An 18-bp duplication in the first exon of the TNFRSF11A gene encoding RANK has been previously identified in four FEO pedigrees. Despite having the identical mutation, phenotypic variations among affected individuals of the same and different pedigrees were noted. Another 18-bp duplication, one base proximal to the duplication previously reported, was subsequently found in two unrelated FEO patients. Finally, mutations overlapping with the mutations found in the FEO pedigrees have been found in ESH and early-onset PDB pedigrees. An Iranian FEO pedigree that contains six affected individuals dispersed in three generations has previously been introduced; here, the clinical features of the proband are reported in greater detail, and the genetic defect of the pedigree is presented. Direct sequencing of the entire coding region and upstream and downstream noncoding regions of TNFRSF11A in her DNA revealed the same 18-bp duplication mutation as previously found in the four FEO pedigrees. Additionally, eight sequence variations as compared to the TNFRSF11A reference sequence were identified, and a haplotype linked to the mutation based on these variations was defined. Although the mutation in the Iranian and four of the previously described FEO pedigrees was the same, haplotypes based on the intragenic SNPs suggest that the mutations do not share a common descent.