Advanced Vertebral Fracture Among Newly Diagnosed Children With Acute Lymphoblastic Leukemia: Results of the Canadian Steroid‐Associated Osteoporosis in the Pediatric Population (STOPP) Research Program

Vertebral compression is a serious complication of childhood acute lymphoblastic leukemia (ALL). The prevalence and pattern of vertebral fractures, as well as their relationship to BMD and other clinical indices, have not been systematically studied. We evaluated spine health in 186 newly diagnosed children (median age, 5.3 yr; 108 boys) with ALL (precursor B cell: N = 167; T cell: N = 19) who were enrolled in a national bone health research program. Patients were assessed within 30 days of diagnosis by lateral thoraco‐lumbar spine radiograph, bone age (also used for metacarpal morphometry), and BMD. Vertebral morphometry was carried out by the Genant semiquantitative method. Twenty‐nine patients (16%) had a total of 75 grade 1 or higher prevalent vertebral compression fractures (53 thoracic, 71%; 22 lumbar). Grade 1 fractures as the worst grade were present in 14 children (48%), 9 patients (31%) had grade 2 fractures, and 6 children (21%) had grade 3 fractures. The distribution of spine fracture was bimodal, with most occurring in the midthoracic and thoraco‐lumbar regions. Children with grade 1 or higher vertebral compression had reduced lumbar spine (LS) areal BMD Z‐scores compared with those without (mean ± SD, ?2.1 ± 1.5 versus ?1.1 ± 1.2; p < 0.001). LS BMD Z‐score, second metacarpal percent cortical area Z‐score, and back pain were associated with increased odds for fracture. For every 1 SD reduction in LS BMD Z‐score, the odds for fracture increased by 80% (95% CI: 10–193%); the presence of back pain had an OR of 4.7 (95% CI: 1.5–14.5). These results show that vertebral compression is an under‐recognized complication of newly diagnosed ALL. Whether the fractures will resolve through bone growth during or after leukemia chemotherapy remains to be determined.     

Platelet tetraspanin complexes and their association with lipid rafts

Tetraspanins are a superfamily of integral membrane proteins that facilitate the organization of membrane and intracellular signaling molecules into dynamic signaling microdomains, tetraspanin-enriched microdomains (TEMs). Four tetraspanin family members have been identified in platelets: CD9, CD151 and TSSC6, which are constitutively associated with alphaIIbbeta3, and CD63, which is present on granule membranes in resting platelets and associates with alphaIIbbeta3-CD9 following platelet activation. CD63 and CD9 associate with a type II phosphatidylinositol 4-kinase, PI4K55, in both resting and activated platelets. Immunoelectron microscopic studies showed co-localization of CD63 and PI4K55 on internal membranes of resting platelets and on the filopodia of thrombin-activated platelets. Because TEMs in malignant cell lines appear to be distinct from prototypic lipid rafts, this study examined whether CD63-PI4K55 and CD9-PI4K55 complexes were resident in platelet-lipid rafts, or formed distinct microdomains. CD63, CD9 and PI4K55 were recovered from low-density membrane fractions (LDMFs) of sucrose gradients following platelet lysis in Brij 35, but unlike lipid-raft proteins were not insoluble in Triton X-100, being absent from LDMFs of platelets lysed with Triton. Incubation of platelets with methyl-beta-cyclodextrin, to deplete cholesterol and disrupt lipid rafts, shifted the complexes to higher density sucrose gradient fractions, but did not disrupt the tetraspanin-PI4K55 complexes. These results demonstrate that tetraspanin complexes in platelets form cholesterol-associated microdomains that are distinct from lipid rafts. It is probable that TEMs and lipid rafts associate under certain conditions, resulting in the close proximity of distinct sets of signaling molecules, facilitating signal transduction.     

Alpha1-antitrypsin deficiency with fatal intracranial hemorrhage in a newborn.

A 4-week-old boy had a fatal intracranial hemorrhage resulting from vitamin K deficiency. The infant had received no vitamin K prophylaxis and was exclusively breastfed. At autopsy, examination of the liver showed cholestasis and fibrosis. DNA was isolated from a blood spot on a Gutherie sample card obtained from the infant for routine metabolic screening. This DNA was used for alpha1-antitrypsin genotyping studies. Genotyping studies identified homozygosity for the point mutation 9989G-->A, confirming a diagnosis of alpha1-antitrypsin deficiency (ZZ phenotype), and resulted in appropriate screening of siblings born after this child's death. Alpha1-antitrypsin deficiency should be considered in the differential diagnosis of infants with late hemorrhagic disease of the newborn. Use of blood from the metabolic screening card as a source of DNA allowed confirmation of this diagnosis after the infant's death.     

Studies in patients with bleeding disorders show that platelet-vessel interaction is important for thromboxane formation in bleeding time wounds

The production of thomboxane B2, the primary metabolite of thromboxane A2, and 6-keto prostaglandin F1 alpha, the primary metabolite of prostacyclin, were measured in response to a standardized vascular injury, the bleeding time, in patients with von Willebrand's disease and in patients with platelet function defects. Compared to controls, thromboxane B2 levels in bleeding time blood were significantly lower in subjects with von Willebrand's disease. In patients with platelet function defects associated with a deficient response to thromboxane A2, thromboxane B2 production in bleeding time blood was similar to controls. In subjects with other platelet function defects, thromboxane production was significantly lower than normal. 6-keto PGF1 alpha production in bleeding time blood was not significantly different in patients compared to controls. The results suggest that bleeding time thromboxane production is influenced by the extent of platelet-vessel interaction.     

The nonerythropoietic component of early bilirubin

The early labeled bilirubin consists of two primary components. The more rapidly synthesized of the two is independent of erythropoiesis (nonerythropoietic), whereas the second fraction is related to red cell production (erythyropoietic). The present studies concern the origin of the nonerythropoietic component.The nonerythropoietic, early labeled bilirubin was studied in bile fistula rats with (delta ALA)-4-(14)C delta aminolevulinic acid and glycine-2-(14)C as precursors. That nephrectomy did not reduce the size of this component despite the large and rapidly turning over pool of renal heme suggests that this pool may be of minor importance in its production. Intoxication with lead to a level that reduced hepatic heme synthesis was associated with a decrease in early bilirubin formation. The synthesis of this bilirubin was assessed in animals with phenobarbital-induced heme protein and cycloheximide-suppressed protein synthesis. Rats pretreated with phenobarbital at a dose level of 60 mg/kg with induction of cytochrome P-450 synthesis showed a minor increase in early labeling when glycine-2-(14)C but not when delta ALA-4-(14)C was used as precursor. Rats given cycloheximide at a dose level that markedly reduced hepatic protein and cytochrome P-450 synthesis but allowed heme synthesis to continue at 60% of its pretreatment level synthesized normal or increased amounts of early bilirubin from delta ALA-4-(14)C. Allylisopropylacetamide intoxication caused little change in early bilirubin formation, whereas aminotriazole given at a time after maximal hepatic heme labeling produced a small but significant increase in the appearance of labeled bilirubin.These findings indicate that early bilirubin production is little influenced by increased hepatic porphyrin synthesis or by changes in the rapidly turning over heme protein P-450. A minimal increase attends catalase inactivation by aminotriazole. Normal or increased synthesis takes place in the presence of suppression of protein synthesis. This finding suggests that the nonerythropoietic early bilirubin may itself consist of two subcomponents. The first of these may arise from free tissue heme or its precursors, and the second may derive from the turnover of the heme proteins. The first subcomponent may serve as a regulatory mechanism for the removal of heme synthesized in excess of its protein acceptor. A composite scheme is proposed for the origin of the total early bilirubin from heme compartments in tissue and marrow.