c-kit mutation and osteopetrosis-like osteopathy in a patient with systemic mast cell disease

Bone mineral density, bone turnover markers and fractures in patients with indolent systemic mastocytosis

OBJECTIVE

We systematically assessed bone mineral density (BMD), bone turnover markers (BTM), and fractures in a large cohort of patients with Indolent Systemic Mastocytosis (ISM).

METHODS

Eighty-two patients (mean age 48 years, 37 women) with ISM were studied. BMD was measured by dual X-ray absorptiometry at the lumbar spine and proximal hip. The serum markers of bone turnover included bone-specific alkaline phosphatase, C-telopeptides of type I collagen, and serum osteocalcin. Previous clinical fractures were registered and spine X-ray was obtained from all patients.

RESULTS

Three women were excluded for concomitant diseases associated to osteoporosis. Osteoporosis according with the WHO classification (T-score<-2.5) was found in 16 patients (20.0%) (7 females and 9 men). Mastocytosis-related low BMD (Z-score at either the spine or the hip<-2) was found in 3 women (9%) and 13 men (28%). The BMD was generally lower at the spine than at the hip. No significant correlation was observed between serum tryptase levels and T or Z-score BMD. One or more moderate or severe vertebral fractures were found in 17 patients (12 men); in 11 of them Z-score values were>-2 or not valuable at the spine. No significant difference was found in the prevalence of mastocytosis-related low BMD and/or vertebral fractures between patients with or without skin involvement. Two patients had radiographic and densitometric osteosclerosis-like characteristics. In osteoporotic patients higher, normal or lower serum BTM were found, without correlations with serum tryptase levels, while in patients with osteosclerosis both BTM and serum tryptase values were particularly increased.

CONCLUSIONS

Vertebral osteoporosis and fractures are frequent in patients with ISM. Spine X-ray and densitometric examination are warranted in all patients, also without skin involvement and particularly in males; Z-score other than T-score BMD must be evaluated. Patients with idiopathic osteoporosis should be evaluated for mast cell disease. Both high than low BTM can be observed in patients with osteoporosis while osteosclerosis is characterized by high bone turnover and serum tryptase levels.

Osteopetrosis-like disease in a cat with respiratory distress

Magnetic resonance (MR) and computed tomography (CT) were performed in an 8-year-old, spayed female cat with chronic effort respiration at the inspiration phase and stertor. Increased bone opacity in the areas of the head, neck and thorax were observed on radiography. MR images showed no signal intensity on both transverse T1WI and T2WI of the nasal cavity. CT revealed increased bone density and hypertrophy of the nasal turbinate and a narrowed nasal passage. From these results, we concluded this case had osteopetrosis-like disease, and that the respiratory distress was caused by hypertrophy of the nasal turbinate.

Systemic Mastocytosis: Clinical Manifestations and Differential Diagnosis

Mast cells produce symptoms by local and remote effects of mediator release and by their presence in increased numbers in normal tissue and bone marrow, where they damage and impair normal organ function. Moreover, mast cells are long-lived and heterogeneous in their response to secretagogues and to inhibitors of mediator release. Clinicians sorting out the diagnosis of SM on the basis of presenting signs and symptoms continue to have their diagnostic skills challenged because of the rarity of this disorder, the fact that many symptoms of SM are present in more common disorders, and the multiple guises that SM may assume at the time of presentation.

Interferon treatment for hypereosinophilic syndromes and systemic mastocytosis

Hypereosinophilic syndromes (HES) and systemic mastocytosis (SMCD) are heterogeneous disorders with clinical symptoms from local and remote effects of excessive proliferation of eosinophils and mast cells, respectively. Interferon alpha (IFN-alpha), alone or in combination with other medications, can be a useful, and at times life-saving, treatment for patients with HES. Receptors for IFN-alpha are present on eosinophils, and clinical benefits are due to its effect on eosinophil proliferation, migration, activation, and survival. These effects are likely mediated through multiple pathways including, but not limited to, inhibition of eosinophil colony-forming cells, upregulation of IFN-gamma synthesis, and inhibition of production of eosinophil-active cytokines by T cells, mast cells, and mononuclear cells. IFN-alpha has been life-saving for patients with intractable HES that were resistant to prednisone, hydroxyurea, and other agents. Resistance to the eosinopenic effect of IFN-alpha does not develop and the dose of IFN-alpha necessary to maintain control of eosinophilia often decreases with time. The combination of IFN-alpha and hydroxyurea is very useful and allows dosage reduction of IFN-alpha and better control of hypereosinophilia than with either agent alone. The efficacy of IFN-alpha for treatment of SMCD has been more difficult to establish, with both favorable and unfavorable results reported. The disparate results may have resulted from the small number of patients with SMCD treated with IFN-alpha, the use of various criteria for a "successful" treatment outcome, short duration of treatment and follow-up, and the use of modest dosages. In reported series, side effects from IFN-alpha have frequently been dose-limiting. IFN-alpha improves many of the clinical symptoms of SMCD including dermatological, hematological, gastrointestinal, and systemic symptoms associated with histamine release. IFN-alpha has a beneficial effect on skeletal symptoms because of its ability to increase bone density and reduce painful episodes from vertebral fractures. No consistent improvement in bone marrow infiltration by mast cells has been demonstrated except in a recent study employing high dosages of IFN-alpha. A beneficial effect from the combination of IFN-alpha and prednisone has been reported for several patients, suggesting that combined use of these two medications may provide synergism in treatment outcomes.

Generalized osteosclerosis in a cat

A 12-year-old, neutered male, domestic long-hair cat was evaluated for a 6-month history of inspiratory stertor and epiphora. In computed tomography of the skull and pelvis, and radiographs of the thorax, right femur and stifle there was generalized osteosclerosis, with obliteration of the nasal turbinates and nasolacrimal duct obstruction. The cat also had a large fibrosarcoma involving the right pelvic limb. Osteosclerosis is a rare disorder that is poorly understood but has been described in several species. Various manifestations, potential causes, and radiologic findings of osteosclerosis are discussed.

Interest of interferon alpha in systemic mastocytosis. The French experience and review of the literature

Systemic mastocytosis (SM) are defined by an abnormal growth and accumulation of mast cells in bone marrow and/or other extracutaneous organs. There is currently no cure for this disease. Because of similarities and/or association of mastocytosis with myeloproliferative disorders, interferon alpha has been tested but with contradictory reported results. A first prospective multicenter phase II trial was then started in France. From 1994 to 1997, 20 adult patients with confirmed bone marrow involvement received interferon alpha-2b for at least 6 months, (from 1 million U per day up to 5 million U/m(2)/day). Thirteen patients who presented systemic and/or specific cutaneous manifestations, demonstrated objective responses: seven (35%) were partial, six (30%) minor but no complete response could be observed at the time of analysis. The bone marrow remained unchanged in 12/13. Thus, interferon should be offered to patients with severe systemic manifestations, who have not responded to symptomatic therapies, even in case of non-aggressive mastocytosis, with or without corticosteroids the first weeks. Long-term therapy should be offered to patients with initial positive response. To control more aggressive SM or mastocytosis associated with clonal hematologic non-mast cell lineage or leukaemia mast cell, other chemotherapeutic regimens should be proposed like Cladribine (2-chlorodeoxyadenosine, 2-CDA) or polychemotherapies including interferon as it is being tested in France in a new multicentric protocol, coordinated by the association AFIRMM, with interferon and oral cytarabine.

Constitutive activation of c-kit by the juxtamembrane but not the catalytic domain mutations is inhibited selectively by tyrosine kinase inhibitors STI571 and AG1296

The c-kit receptor tyrosine kinase (KIT) is constitutively activated by 2 types of naturally occurring mutations, the Val559-->Gly (G559) mutation in the juxtamembrane domain and the Asp814-->Val (V814) mutation in the catalytic domain. We evaluated the effects of the tyrosine kinase inhibitors STI571 and AG1296 on BaF3 cells expressing wild-type KIT (KIT(WT)) or activating mutants of KIT (KIT(G559) and KIT(V814)) in the presence or absence of the KIT ligand, stem cell factor (SCF). Both STI571 and AG1296 inhibited SCF-dependent activation of KIT(WT) and SCF-independent activation of KIT(G559) more efficiently, whereas SCF-independent activation of KIT(V814) was scarcely affected. Furthermore, both inhibitors inhibited SCF-dependent growth of BaF3-KIT(WT) cells and, with higher potencies, SCF-independent growth of BaF3-KIT(G559) cells through the induction of apoptosis. In contrast, the inhibitors had little or no effect on SCF-independent growth of BaF3-KIT(V814) cells or on IL-3-dependent growth of BaF3-Mock cells. These results suggested that both inhibitors may be effective therapeutic agents for oncogenic KIT with the juxtamembrane domain mutation, but not with the catalytic domain mutation, and that the activation mechanism of the catalytic domain mutant KIT is complex and entirely different from that of the wild-type KIT or the juxtamembrane domain mutant KIT.

Bone marrow angiogenesis in systemic mast cell disease

Mast cells may participate in tumor angiogenesis through the release of angiogenic cytokines from their secretory granules. To gain additional insight into the role of mast cells in bone marrow angiogenesis, we performed a semiquantitative measurement of bone marrow microvessel density in 52 consecutive adult patients with systemic mast cell disease (SMCD). The results were examined for potential correlations with mast cell expression of angiogenic cytokines and with other histologic features of the bone marrow. Standard immunohistochemical methods were used to visualize bone marrow microvessels (CD34 staining) and mast cell expression of transforming growth factor-beta, basic fibroblast growth factor, and their respective receptors. An increase in microvessel density was demonstrated in 32 of the 52 patients (62%) with SMCD, and the degree of bone marrow angiogenesis did not correlate with either the mast cell expression pattern of the study cytokines or the presence (23 patients) or absence (29 patients) of an associated hematologic disorder. In the 29 patients without an associated hematologic disorder, microvessel density was correlated significantly with the presence of an abnormal pattern of hematopoiesis but not with the degree of bone marrow involvement by mast cells. Furthermore, areas occupied by mast cell lesions were often devoid of neovascularization. We conclude that bone marrow angiogenesis characterizes a percentage of patients with SMCD and that the pathogenesis may not necessarily be linked to the mast cells themselves.

Mutation analysis of C-KIT in patients with myelodysplastic syndromes without mastocytosis and cases of systemic mastocytosis

The proto-oncogene C-KIT encodes a tyrosine kinase receptor that is expressed on mast cells and haematopoietic stem cells and can show somatic mutations in patients with mastocytosis. Only scattered information is available about mutations in C-KIT in patients with other myeloid neoplasms. Moreover, the prevalence of mutations in C-KIT in bone marrow specimens of individuals with systemic mastocytosis is largely unknown. Using sequence analysis, we have screened cDNAs of the C-KIT domain encompassing codon 510-626 and codon 763-858 in bone marrow (BM) mononuclear cells (MNCs) of patients with myelodysplastic syndromes (n = 28) and patients with systemic mastocytosis (n = 12) for the presence of mutations. Furthermore, restriction fragment length polymorphism analysis was applied for identification of the C-KIT 2468A-->T and the C-KIT 1700T-->G mutation, as well as the C-KIT 1642A-->C polymorphism. All 11 patients with systemic indolent mastocytosis tested positive for C-KIT 2468A-->T. In contrast, no mutation was identified in the case of aggressive mastocytosis. Among patients with myelodysplastic syndromes, no patient showed a somatic mutation in C-KIT. The allele frequency for C-KIT 1642A-->C among the entire patient population was 0.038 and was 0.125 among age- and sex-matched healthy controls. Our data demonstrate that myelodysplastic syndromes without histological or cytological evidence of mastocytosis do not exhibit somatic mutations in exons 10, 11, 12, 16, 17 and 18 of C-KIT. In contrast, BM MNCs of patients with systemic indolent mastocytosis were all positive for C-KIT 2468A-->T and negative for additional mutations in these exons. The C-KIT 1642A-->C polymorphism is not associated with myelodysplastic syndrome or systemic mastocytosis.

Treatment of systemic mast cell disorders

The heterogeneous nature of disease manifestations in mastocytosis requires the individualization of therapy to each patient's clinical presentation and prognosis. The mainstay of treatment for most categories of mastocytosis are H1 and H2 antihistamines with the addition of corticosteroids for more severe symptoms. This article presents a summary of treatment strategies for indolent and aggressive forms of mastocytosis along with a discussion of future therapeutic directions.