PTHrP-independent hypercalcemia with increased proinflammatory cytokines and bone resorption in two children with CD19-negative precursor B acute lymphoblastic leukemia.

Hypercalcemia in childhood acute lymphoblastic leukemia (ALL) is rare and occasionally associated with parathyroid hormone-related protein (PTHrP). However, the pathogenesis of PTHrP-independent hypercalcemia remains unclear. We report two children with precursor B ALL who had marked hypercalcemia (15.8 and 16.6 mg/dl, respectively) and disseminated osteolysis. Serum tumor necrosis factor-alpha (TNF-alpha) and IL-6 were markedly elevated, whereas 1,25(OH)(2) vitamin D(3), intact PTH and PTHrP were decreased or undetected. Analysis of urinary deoxypyridinoline (DPY) or bone biopsy of the osteolytic lesion showed an increased bone resorption, and administration of bisphosphonate improved the hypercalcemia. Patients had ALL with immunophenotype positive for CD10, CD34, and HLA-DR but negative for CD19 and obtained remission with chemotherapy. These findings suggest that increased osteoclastic bone resorption via stimulation with TNF-alpha and IL-6 may be mechanism causing PTHrP-independent hypercalcemia in some patients with precursor B ALL lacking CD19 expression.

Functional analysis of PTPN11/SHP-2 mutants identified in Noonan syndrome and childhood leukemia.

Noonan syndrome (NS) is characterized by short stature, characteristic facial features, and heart defects. Recently, missense mutations of PTPN11, the gene encoding protein tyrosine phosphatase (PTP) SHP-2, were identified in patients with NS. Further, somatic mutations in PTPN11 were detected in childhood leukemia. Recent studies showed that the phosphatase activities of five mutations identified in NS and juvenile myelomonocytic leukemia (JMML) were increased. However, the functional properties of the other mutations remain unidentified. In this study, in order to clarify the differences between the mutations identified in NS and leukemia, we examined the phosphatase activity of 14 mutants of SHP-2. We identified nine mutations, including a novel F71I mutation, in 16 of 41 NS patients and two mutations, including a novel G503V mutation, in three of 29 patients with leukemia. Immune complex phosphatase assays of individual mutants transfected in COS7 cells showed that ten mutants identified in NS and four mutants in leukemia showed 1.4-fold to 12.7-fold increased activation compared with wild-type SHP-2. These results suggest that the pathogenesis of NS and leukemia is associated with enhanced phosphatase activity of mutant SHP-2. A comparison of the phosphatase activity in each mutant and a review of previously reported cases showed that high phosphatase activity observed in mutations at codons 61, 71, 72, and 76 was significantly associated with leukemogenesis.

Wild-type phenylalanine hydroxylase activity is enhanced by tetrahydrobiopterin supplementation in vivo: an implication for therapeutic basis of tetrahydrobiopterin-responsive phenylalanine hydroxylase deficiency.

We previously proposed a novel disease entity, tetrahydrobiopterin (BH4)-responsive phenylalanine hydroxylase (PAH) deficiency, in which administration of BH4 reduced elevated levels of serum phenylalanine [J. Pediatr. 135 (1999) 375-378]. Subsequent reports indicate that the prevalence of BH4-responsive PAH deficiency is much higher than initially anticipated. Although growing attention surrounds treatment with BH4, little is known about the mechanism of BH4 responsiveness. An early report indicates that BH4 concentration in rat liver was 5 microM where Km for BH4 of rat PAH was estimated to be 25 microM in an oxidation experiment using a liver slice, suggesting relative insufficiency of BH4 in liver in vivo. In the present study, we developed a breath test for mice using [1-13C]phenylalanine in order to examine the BH4 responsiveness of normal PAH in vivo. The reliability of the test was verified using BTBR mice and its mutant strain lacking PAH activity, Pahenu2. BH4 supplementation significantly enhanced 13CO2 production in C57BL/6 mice when phenylalanine was pre-loaded. Furthermore, BH4 apparently activated PAH in just 5 min. These observations suggest that submaximal PAH activity occurs at the physiological concentrations of BH4 in vivo, and that PAH activity can be rapidly enhanced by supplementation with BH4. Thus, we propose a possible hypothesis that the responsiveness to BH4 in patients with PAH deficiency is due to the fact that suboptimal physiological concentrations of BH4 are normally present in hepatocytes and the enhancement of the residual activity may be associated with a wide range of mutations.

Alteration in the cellular response to retinoic acid of a human acute promyelocytic leukemia cell line, UF-1, carrying a patient-derived mutant PML-RARalpha chimeric gene.

Cellular response to all-trans retinoic acid (ATRA) of acute promyelocytic leukemia (APL) with patient-derived mutant PML-retinoic acid receptor-alpha (PML-RARalpha) was investigated using an APL cell line, UF-1, carrying Arg611Trp mutation in PML-RARalpha. Although the mutant protein showed a decreased ligand-dependent transcriptional activity and retained a dominant-negative effect on normal RARalpha, UF-1 cells underwent growth inhibition, maturation and apoptosis in response to ATRA at 1 microM, but not < or = 100 nM, after 4 days of treatment with ATRA. Moreover, in the presence of 1 microM ATRA, approximately 50% of UF-1 cells expressing annexin V, an early-apoptotic marker, was negative for CD11b and showed immature morphology. These findings suggest that UF-1 cells, despite expressing mutant PML-RARalpha protein, can be induced by ATRA to undergo differentiation and apoptosis through RA-inducible mechanism(s), in which a proportion of apoptosis may occur independent of terminal differentiation. This unique cell line may be useful for investigating the pathogenesis of ATRA resistance and the mechanism of ATRA-induced apoptosis in APL.

Acute renal failure due to leukemic cell infiltration followed by relapse at multiple extramedullary sites in a child with acute lymphoblastic leukemia.

Acute renal failure due to leukemic infiltration into the kidney is rare in childhood acute lymphoblastic leukemia (ALL). We report here a five year-old boy with ALL who presented acute renal failure caused by leukemic infiltration at onset. Treatment with predonisolone and hemodialysis was effective. However, he showed persistent or repeated relapses at extramedullary sites, such as central nervous system, testis, and pancreas, suggesting that leukemic cells of this patient may have had a high affinity to extramedullary organs. On the basis of previous reports and the experience of this patient, intensive treatment may be needed in ALL children with renal involvement.