platelet dysfunction and increased bleeding tendency in mccune-albright syndrome
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CLINICAL AND LABORATORYOBSERVATIONS
Platelet Dysfunction and Increased Bleeding Tendency inMcCune-Albright Syndrome
ANURAG BAJPAI, MD, ANTHEA GREENWAY, FRACP, AND MARGARET ZACHARIN, FRACP
We observed increased bleeding tendency and platelet function abnormalities in 3 boys with McCune-Albright syndromeMAS). We speculate that platelet dysfunction contributed to excessive blood loss in our patients. This report of plateletysfunction in MAS highlights the need for assessment of platelet functions in the condition. (J Pediatr 2008;153:287-9)
cCune Albright syndrome (MAS) is a sporadic disorder caused by activating somatic mutations in the GNAS gene.1
This gene codes for the stimulatory subunit of G protein (Gs�) involved in cyclic adenosine monophosphate (AMP)synthesis. Activating mutations in the gene cause constitutional activation of the Gs � protein, resulting in persistently
levated cyclic AMP levels. The somatic nature of expression is responsible for variable clinical manifestations of the disorder.AS usually presents with a constellation of cutaneous (multiple café-au-lait spots), skeletal (polyostotoic fibrous dysplasia), and
ndocrine (growth hormone excess, precocious puberty, hyperthyroidism, and phosphate wasting) features.2 Reduced platelets� activity and increased platelet aggregation has been reported in pseudohypoparathyroidism I (PHP I), a disorder associatedith inactivating GNAS mutations.3,4 As the mutation in MAS is an activating mutation of the same gene, this suggests theossibility of an opposite type of platelet dysfunction in MAS. Increased perioperative blood loss has been reported in subjectsith MAS undergoing orthopedic procedures and has previously been attributed to increased vascularity of the dysplastic bone.5
owever, the role of other possible contributory factors like platelet dysfunction has not been evaluated. We observed increasederioperative blood loss in 3 boys with MAS, which we speculated might be caused by platelet dysfunction.
METHODSPlatelet functions were assessed with the platelet function analyzer (PFA 100), a screening test for platelet dysfunction.
he PFA 100 aims at replicating the process of primary hemostasis in vitro by exposing platelets within citrated whole bloodo high shear stress within a capillary.6 The capillary is coated with collagen and platelet agonist adenosine diphosphate (ADP)r epinephrine. Formation of a hemostatic plug by the platelets results in reduction in flow rate. The time taken for blood flowo cease (closure time) is an indicator of platelet function, with increased closure time being a marker of platelet dysfunction.atients with abnormal PFA 100 results underwent detailed platelet agregometery. This was done by examining the responsef platelets to different concentrations of platelet agonists (ADP, collagen, and ristocetin). No aggregation or monophasicesponse with disaggregation after exposure to an agonist indicates impaired plateletesponsiveness to that agonist and suggests platelet dysfunction.
CASE REPORTS
ase 1This boy presented at the age of 4 months with multiple café-au-lait spots and bony
eformities. With radiological evaluation, the presence of polyostotic fibrous dysplasia wasonfirmed, indicating a diagnosis of MAS. This was confirmed by the demonstration ofn activating GNAS mutation (cysteine instead of arginine at position 201, R201C). Heas treated with intravenous pamidronate for extensive fibrous dysplasia, management of
evere bone pain, and multiple, repeated fractures.7 Other manifestations of MASncluded hyperthyroidism requiring radioactive iodine ablation and hypophosphatemia.
DP Adenosine diphosphateMP Adenosine monophosphate
PFA Platelet function analyzerPHP I Pseudohypoparathyroidism I
From the Departments of Endocrinologyand Diabetes (A.B., M.Z.) and the Depart-ment of Haematology (A.G.), Royal Chil-dren’s Hospital, Melbourne, Victoria, Aus-tralia.
Submitted for publication Jun 22, 2007; lastrevision received Dec 11, 2007; acceptedFeb 25, 2008.
Reprint requests: Dr Margaret Zacharin,Department of Endocrinology and Diabe-tes, Royal Children’s Hospital, FlemingtonRoad, Parkville, Melbourne, Victoria, 3052,Australia. E-mail: [email protected].
0022-3476/$ - see front matter
Copyright © 2008 Mosby Inc. All rightsreserved.
AS McCune-Albright syndrome
10.1016/j.jpeds.2008.02.045287
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here were no other endocrinopathies. He underwent hu-eral osteotomy and intramedullary rod insertion at the age
f 13 years, for management of severe distortion of the af-ected area of humerus, because of repeated fractures and bonyxpansion. This was associated with significant perioperativelood loss, resulting in a decrease in hemoglobin levels from2.1 g/dL (121 g/L) to 4 g/dL (40 g/L). He required multiplelood transfusions because of significant bleeding. There waso history of spontaneous bleeding, family history of bleedingisorders, or exposure to anti-platelet medications.
An examination for increased bleeding tendency re-ealed platelet count, prothrombin time, activated partialhromboplastin time, von Willibrand factor, and fibrinogenevels within reference range (Table I). PFA 100 study dem-nstrated increased ADP closure time (121 seconds; referenceange, 74-120 seconds) with normal epinephrine closure time177 seconds; reference range, 94-193 seconds). ImpairedDP response was confirmed with platelet aggregometery
tudies that showed no aggregation after exposure to 2.5mol ADP and monophasic response and disaggregationfter exposure to higher ADP concentrations (5 and 10 �mol;able II). Normal aggregation was observed in response to
ollagen (2 and 4 �g/mL) and ristocetin (0.5 and 1.5 ng/mL).diagnosis of platelet dysfunction was established.
After demonstration of the platelet function defect, theatient underwent a preoperative platelet transfusion beforeubsequent femoral osteotomy. This procedure was similar tohe initial intervention in trauma and duration. Indeed, theone size was significantly larger (femur compared with hu-erus). The whole femur was also severely expanded by
brous dysplasia. In contrast to the earlier surgery, perioper-tive blood loss related to this procedure was minimal, with aostoperative hemoglobin level of 11.4 g/dL (114 g/L), witho need for blood transfusion. A recent fall resulted in frac-ure of the mid shaft of the humerus, again requiring internalxation with an intramedullary rod. He underwent a platelet
able I. Screening investigations for bleedingendency observed in the series
Investigations Case 1 Case 2 Case 3Reference
range
latelet count, 109/L 184 302 224 150-400T, seconds 14.3 13.1 12.4 11.5-14.5PTT, seconds 34 31 33 27-39WF antigen, % 114% 140% 120% 50-150ollagen binding
activity, %120% 128% 132% 50-150
ibrinogen, g/L 3.7 3.6 3.2 1.9-4.3FA 100ADP closure
time, seconds121 135 127 74-120
Epinephrineclosure time
177 175 176 94-193
T, Prothrombin time; APTT, activated partial thromboplastin time; vWF, von Willi-rand factor.
ransfusion before this procedure, which was virtually identi- o
88 Bajpai, Greenway, and Zacharin
al to the original one that caused the severe blood loss. Onhis occasion, blood loss was again negligible, and no trans-usion was required.
ase 2This boy was diagnosed with MAS in infancy, on the
asis of the presence of multiple café-au-lait spots and poly-stotic fibrous dysplasia. This was confirmed by the demon-tration of an activating GNAS mutation (R201C) in periph-ral blood. He had extensive fibrous dysplasia, resulting inony deformities and bone pain, and was treated with intra-enous pamidronate treatment. There were no endocrinopa-hies.
Femoral osteotomy was performed at the age of 15 yearsnd 6 months. This was associated with severe blood loss,esulting in a decrease in hemoglobin levels from 12 g/dL120 g/L) to 6.4 g/dL (64 g/L), mandating multiple bloodransfusions. There was no history of exposure to anti-plateletedications. An examination for increased bleeding tendencyas non-contributory, with the exception of prolonged PFA00 ADP closure time (135 seconds; reference range, 74-120econds). With detailed aggregometery studies, a plateletunction abnormality with monophasic response and disag-regation after exposure to different concentrations of ADP2.5, 5 and 10 �mol) were confirmed. Response to collagen,pinephrine, and ristocetin was normal. The patient under-ent a preoperative platelet transfusion before a subsequent
emoral osteotomy. This was effective in reducing postoper-tive blood loss, with no need for blood transfusion at theatter procedure and a postoperative hemoglobin level of 12.2/dL (122 g/L).
ase 3MAS was diagnosed in this boy in infancy on the basis
f the presence of multiple café-au-lait spots and polyostoticbrous dysplasia. This was confirmed by the demonstration oftypical GNAS mutation in the blood (R201C). He was
reated with intravenous pamidronate for fibrous dysplasia.he only endocrinopathy noted was of mild precocious pu-erty that did not require treatment. At the age of 9 years, head significant blood loss during a femoral osteotomy, result-
ng in a decrease in hemoglobin levels from 12.4 g/dL (124/L) to 8.6 g/dL (86 g/L). He was not taking any anti-plateletedications. The only abnormality noted on his bleeding
valuation was prolonged PFA 100 ADP closure time (127econds; reference range, 74-120 seconds) with normal epi-ephrine closure time (176 seconds; reference range, 94-193econds). Aggregometery studies confirmed these findings,ith selective impairment in response to ADP in the wake ofnormal response to other agonists. A preoperative platelet
ransfusion resulted in reduced blood loss during a subsequentrthopedic procedure, with a postoperative hemoglobin level
f 11.3 g/dL (113 g/L).The Journal of Pediatrics • August 2008
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DISCUSSIONIncreased blood loss during orthopedic surgery in MAS
reviously has been attributed to increased vascularity of dys-lastic bone.5 Although this definitely contributes to in-reased blood loss in MAS, the role of other factors, such aslatelet dysfunction, has not been evaluated. We speculatehat the demonstration of platelet dysfunction and markededuction in the amount of perioperative blood loss after these of platelet transfusion suggests an important contributoryole of platelet dysfunction in the pathogenesis of bleedingendency of our patients.
Although the cause of platelet dysfunction in our pa-ients is unclear, it appears to be related to increased intra-latelet cyclic AMP levels, caused by constitutional Gs�ction. Identification of platelet aggregation abnormalities inisorders of the GNAS-Gs� system suggests an importantole of the system in the regulation of platelet functions. Aunctional polymorphism in the gene encoding the extra largetimulatory G protein � subunit has been linked with plateletysfunction and increased bleeding tendency.8 This has beenttributed to increased platelet Gs� activity, a finding con-rmed with in vitro studies.9 This and the observation of anpposite type of platelet dysfunction, resulting in increasedoagulation, in PHP I, a disorder characterized by reduceds� activity, suggests an important role of the GNAS-Gs�-
yclic AMP system in platelet aggregation.4 On the basis ofhese observations, it is likely that elevated intra-platelet cyclicMP levels interfere with platelet aggregation.
An interesting aspect of these patients is the unusualattern of platelet dysfunction. PFA 100 studies showedncreased ADP closure time in the presence of normal epi-ephrine closure time. In contradistinction to our findings ofelective prolongation in ADP closure time, prolonged ADPlosure time is usually associated with prolonged epinephrinelosure time. Aggregometery studies confirmed this unusualbnormality and provided an insight to the pathophysiologyf platelet dysfunction in our patients. The platelet aggrega-ory effect of ADP is mediated by the G protein linked2Y12 receptor. ADP binding to the P2Y12 receptor acti-ates Gi protein, which inhibits intra-platelet cyclic AMProduction.10 This triggers a chain of events, culminating inlatelet aggregation. Constitutionally active Gs� protein in
able II. Platelet agregometery responses observed
Agonist Concentration Case 1
DP 2.5 �mol No aggregationDP 5 �mol Monophasic with disaggregationDP 10 �mol Monophasic with disaggregationollagen 2 �g/mL Normal aggregationollagen 4 �g/mL Normal aggregationistocetin 0.5 ng/mL Normal aggregationistocetin 1.5 ng/mL Normal aggregation
AS would interfere with the cyclic AMP lowering effect of1T
latelet Dysfunction and Increased Bleeding Tendency in McCune-Albrig
DP, resulting in platelet dysfunction. However, the aggre-atory effects of other platelet agonists are cyclic AMP inde-endent and therefore preserved in MAS.
Our study highlights the importance of the assessmentf platelet function in MAS. Because of the somatic nature ofhe disease, platelet dysfunction would occur only when theNAS mutation was present in a substantial proportion of
latelet population. Moreover, platelet dysfunction is ex-ected to represent a spectrum ranging from no abnormalityo mild dysfunction to clinically significant bleeding. All ourubjects had severe disease, with the GNAS mutation detect-ble in peripheral blood. There is a need for evaluation oflatelet function in larger series of patients with a widepectrum of severity of MAS, to characterize the extent andignificance of platelet dysfunction in the condition. Becausef the mild nature of platelet dysfunction observed in ouratients, spontaneous bleeding is unlikely. However, life-hreatening bleeding may occur during surgical intervention,
frequent necessity in MAS. We therefore propose thatlatelet function should be assessed in patients with MASho undergo invasive procedures.
REFERENCES. Weinstein LS, Shenker A, Gejman PV, Merino MJ, Friedman E, Spiegel AM.ctivating mutations of the stimulatory G protein in the McCune-Albright syndrome.Engl J Med 1991;325:1688-95.
. Zacharin M. The spectrum of McCune Albright syndrome. Pediatr Endocrinolev 2007;4 Suppl 4:412-8.. Freson K, Thys C, Wittevrongel C, Proesmans W, Hoylaerts MF, Vermylen J,t al. Pseudohypoparathyroidism type Ib with disturbed imprinting in the GNAS1luster and Gsalpha deficiency in platelets. Hum Mol Genet 2002;11:2741-50.. Faull CM, Welbury RR, Paul B, Kendall-Taylor P. Pseudohypoparathyroidism: itshenotypic variability and associated disorders in a large family. Q J Med 1991;78:251-64.. Ippolito E, Caterini R, Farsetti P, Potenza V. Surgical treatment of fibrous dysplasiaf bone in McCune-Albright syndrome. J Pediatr Endocrinol Metab 2002;15:939-44.. Favaloro EJ. Clinical application of the PFA-100. Curr Opin Hematol 2002;:407-15.. Chan B, Zacharin M. Pamidronate treatment of polyostotic fibrous dysplasia:ailure to prevent expansion of dysplastic lesions during childhood. J Pediatr Endocrinol
etab 2006;19:75-80.. Freson K, Hoylaerts MF, Jaeken J, Eyssen M, Arnout J, Vermylen J, et al. Geneticariation of the extra-large stimulatory G protein alpha-subunit leads to Gs hyperfunc-ion in platelets and is a risk factor for bleeding. Thromb Haemost 2001;86:733-8.. Freson K, Jaeken J, Van Helvoirt M, de Zegher F, Wittevrongel C, Thys C, et al.unctional polymorphisms in the paternally expressed XLalphas and its cofactor ALEXecrease their mutual interaction and enhance receptor-mediated cAMP formation.um Mol Genet 2003;12:1121-30.
e series
Case 2 Case 3
onophasic with disaggregation Monophasic with disaggregationonophasic with disaggregation Reduced aggregationonophasic with disaggregation Reduced aggregationormal aggregation Normal aggregationormal aggregation Normal aggregationormal aggregation Normal aggregationormal aggregation Normal aggregation
in th
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0. Hechler B, Cattaneo M, Gachet C. The P2 receptors in platelet function. Seminhromb Hemost 2005;31:150-61.
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