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Cerebrovascular accidents in children with sickle-cell disease and alpha-thalassemia
CLINICAL AND LABORATORY OBSERVATIONS
Cerebrovascular accidents in children with sickle-cell disease and alpha-thalassemia S c o t t T. Miller, MD, Ronald F. Rieder, MD, Sreedhar P. Rao, MD, a n d A u d r e y K. Brown, MD From the Department of Pediatrics, Divisionof Hematology/Oncology, and the Department of Medicine, Divisionof Hematology, State Universityof New York-Health Science Center at Brooklyn
Alpha-thalassemia occurs commonly in black Americans, ~ with approximately 30% lacking one a-glob{n gene (athai-2 genotype: aa/a-) and 4% lacking two genes (athai- 1 genotype: a - / a - or, rarely, aa/--). In individuals with sickle-cell disease, a-thalassemia attenuates some of the hematologic manifestations, 2-4 although the extent of clinical benefit remains controversial?. 5 Before routine implementation of long-term transfusion programs for children with sickle-cell disease and cerebrovascular accident, 6,7 CVA was ~i significant cause of death in the young sickle-cell disease population? Because the favorable effects of a-thalassemia on hematologic manifestations are apparent by the age of 1 year, 9 it is possible that a reduction in incidence of CVA, which occurs at a mean age of 7 years, s might contribute to prolonged survivaP in patients with sickle cell-a-thalassemia. In fact, a reduced incidence of a-thalassemia has been reported in a small group of patients with sickle-cell disease who have had a CVA? ~ The a-globin gene status of 20 of our sickle-cell disease patients with a history of CVA has been ascertained and is the basis for this report. METHODS
Subjects. All 20 patients with a history of CVA and currently receiving long-term transfusion therapy at this institution were studied. Median age of the patients at the time of diagnosis of CVA was 7 years (range 2 to 15 years), and all have been on a transfusion regimen to keep pretransfusion hemoglobin S levels <30% for 1 to 12 years (median 6 years); it is our current policy to continue transfusion indefinitely. Most patients receive transfusion of frozen-thawed deglycerolized packed red blood cells at 3-week intervals. All had clinical and laboratory values Submitted for publication May 2, 1988; accepted June 14, 1988. Reprint requests: Scott T. Miller, MD, SUNY-Health Science Center at Brooklyn, Department of Pediatrics, 450 Clarkson Ave., Box 49, Brooklyn, NY 11203.
compatible with the diagnosis of homozygous sickle-cell anemia before the institution of transfusion therapy. All had an acute onset of weakness of an extremity persisting at least 48 hours, with or without additional neurologic signs. Computed tomography scans done at an early stage in 17 of 20 patients (including all with a-thai-2) did not show intracranial hemorrhage. a-Gene analysis. Blood was obtained in calcium-ethylenediaminetetraacetic acid immediately before transfusion; DNA was prepared from the leukocytes. Aliquots were digested with restriction enzymes Bam HI and Bgl II and subjected to electrophoresis on agarose gel as previousCVA CT
Cerebrovascular accident Computed tomography
]
ly described. N After transfer to nitrocellulose paper, the blots were hybridized to a 32p-labeled a-complementary D N A probe and analyzed by autoradiography. RESULTS A single a-globin gene deletion (a-thai-2) was present in 5 of 20 (25%) patients; none had a-thai-1. The clinical and laboratory findings in these five patients with a-thai-2 sickle-cell disease are listed in the Table. Patient 5 was less anemic than is usual for patients with homozygous sicklecell disease; otherwise, a-thal-2 patients did not differ significantly from those with the normal allotment of a-globin genes. The a-thai-2 group included both our oldest and our youngest patients with CVA. Patient 1 had a CVA 4 months after completing 1 year of regular transfusion therapy for recurrent splenic sequestration; she underwent splenectomy at age 8 years after a sequestration episode that occurred during transfusion therapy. One patient in the non-a-thai group also has undergone splenectomy because of increased transfusion requirements and hypersplenism.
847
848
Clinical and laboratory observations
The Journal of Pediatrics November 1988
Table. Clinical and laboratory findings (before transfusion) in patients with sickle-cell disease, a-thai-2, and C V A Patient No. 1 2 3 4 5
Age at CVA (yr) 2V3 6 6 7 15
Neurologic findings
Hemoglobin (gm/dl)
MCV (fl)
Reticulocytes (%)
L hemiparesis R hemiparesis L hemiparesis R hemiparesis Convulsions, coma, quadriparesis
7.6 8.7 7.5 7.5 10.4
87 96 NA NA 91
13.7 11.7 15.0 9.5 6.5
MCV, Mean corpuscular volume;NA, not available.
DISCUSSION Cerebrovascular accidents in children with sickle-cell disease are most often due to stenotic or occlusive lesions of large or middle-caliber cerebral arteries. 7 These lesions are associated with intimal fibromuscular proliferation, perhaps as a result of damage to vascular endothelium by abnormal adherence of sickled cells. 7 Because c~-thalassemia-sickle cell patients have lower numbers of irreversibly sickled cells, 3 it was reasonable to postulate that endothelial damage may be less severe and thus that the risk of stroke may be diminished in this group of patients, particularly because the favorable influence of ~-thalassemia on various hematologic measurements is apparent at an early a g e ) Patients doubly heterozygous for sickle hemoglobin and either/3-thalassemia or hemoglobin C are at diminished risk for CVA, 12 although this protection is not absolute. 12,13 Twenty-five percent of our sickle-cell disease patients with C V A did, however, have concomitant c~-thal-2, a figure similar to that seen in the general American black population, l Patient characteristics were indistinguishable from those with the normal c~-globin genotype. No patients with C V A had c~-thal-1, although the small number of patients examined precludes suggesting that patients with a two-gene deletion may be protected from CVA. In a small group of pediatric patients with C V A reported by Piomelli et al., ~~c~-thal-1 patients were also not present; it may be that the more substantial improvement in hematologic values associated with c~-thal-12 will indeed be shown to exert a protective effect when larger numbers of patients are analyzed. Our data do not support the finding by Piomelli et al. that a single c~-gene deletion protects from stroke in sickle-cell anemia. One of our patients with c~-thal-2 had splenic sequestration episodes before her C V A and also subsequently, while on a long-term transfusion program. An association between c~-thalassemia and splenic sequestration was reported previouslyl4; however, sequestration in this patient was unexpected, because long-term transfusion therapy
has been recommended as an effective means of preventing recurrent sequestration in patients with homozygous sickle-cell disease who have had a sequestration episode. 15 It is possible that sickle cell-c~-thalassemia patients are for some reason less protected from sequestration by transfusion than are patients with sickle-cell disease who have a normal allotment of c~-globin genes. We thank Diane Jensen and Laurene Pollio for assistance in the clinical care of our patients.
REFERENCES
1. Dozy AM, Kan YW, Embury SH, et al. Alpha globin gene organization in blacks precludes the severe form of alphathalassemia. Nature 1979;280:605-7. 2. Embury SH, Dozy AM, Miller J, et al. Concurrent sickle cell anemia and cr N Engl J Med 1982;306:270-4. 3. Higgs DR, Aldridge BE, Lamb J, et al. The interaction of alpha-thalassemia and homozygous sickle-cell disease. N Engl J Med 1982;306:1441-6. 4. Steinberg MH, Rosenstock W, Coleman MB, et al. Effects of thalassemia and microcytosis on the hematologic and vasoocclusive severity of sickle cell anemia. Blood 1984;63:135360. 5. Mears G J, Laehman HM, Labie D, Nagel RL. Alphathalassemia is related to prolonged survival in sickle cell anemia. Blood 1983;62:286-90. 6. Sarnaik S, Soorya D, Kim J, et al. Periodic transfusions for sickle cell anemia and CNS infarction. Am J Dis Child 1979;133:1254-7. 7. Russell MO, Goldberg HI, Hodson A, et al. Effect of transfusion therapy on arteriographic abnormalities and on recurrence of stroke in sickle cell disease. Blood 1984;63: 162-9. 8. Powars DR, Wilson B, Imbus C, et al. The natural history of stroke in sickle cell disease. Am J Med 1978;65:461-71. 9. Stevens MCG, Maude GH, Beckford M, et al. Thalassemia and the hematology of homozygous sickle cell disease in childhood. Blood 1986;67:411-4. 10. Piomelli S, Seaman C, Cirella B, et al. Does alpha-thalassemia protect from early stroke in sickle cell anemia [Abstract]? Pediatr Res 1986;10:285A. 11. Safaya S, Multaney P, Rieder RF. Dysfunctional a-globin genes in hemoglobin H disease in blacks: variation in restric-
Volume 113 Number 5
tion fragment size permits the detection of the -c~/-c~v genotype. Am J Hematol 1987;26:329-39. 12. Sarnaik SA, Lusher JMi Neurological complications of sickle cell anemia. Am J Pediatr Hematol/Oncol 1982;4:386-94. 13. Fabian RH, Peters BH. Neurological complications of hemoglobin SC disease. Arch Neurol 1984i4h289-92. 14. Mears JG, Schoenbrun M, Schaefer KE, et al. Frequent
Clinical and laboratory observations
849
association of alpha-thalassemia with splenic sequestration crisis and splenomegaly in sickle cell subjects [Abstract]. Blood 1982;60(suppl 1):47a. 15. Rao S, Gooden S. Splenic sequestration in sickle cell disease: role of transfusion therapy. Am J Pediatr Hcmatol/Oncol 1985;7:298-301.
Interested readers may want to compare the older patients discussed in the following article with the neonates described by Manco-Johnson et al., in the August 1988 issue (J PEDIATR 1988;112:35963). -J.M.G.
Temporary protein C deficiency associated with cerebral arterial thrombosis in childhood Anne Dusser, MD, Catherine Boyer-Neumann, MD, and Martine Wolf From the Universit6 Paris-Sud, D~partement de P6diatrie, Unite de Neurop6diatrie and Laboratoire d'H6matologie, HOpital Bicetre, Kremlin-Bic~tre, France
Protein C in association with its cofactor protein S (both vitamin K-dependent plasma proteins) is a potent anticoagulant that regulates coagulation by inhibiting activated cofactors V and VIII C and by stimulating fibrinolysis. The association of recurrent venous thrombosis and hereditary protein C deficiency has been reported since 1981, ~4 suggesting the existence of a relationship between thrombosis and protein C deficiency. We report two observations of cerebral arterial thrombosis associated with a partial and temporary plasma protein C deficiency. METHODS Protein C antigen was measured by enzyme-linked immunosorbent assay, as described previously, s When the PPC antigen value was found to be decreased, PPC activity was also determined by a method based on the ability of activated protein C to prolong the activated partial thromboplastin time of normal plasma. 6 Protein C antigen and activity were expressed in units per milliliter, 1 unit being defined as the amount of protein C present in 1 ml of reference plasma, which was obtained from a pool of 25 healthy donors and stored at - 8 0 ~ C in small aliquots. At the ages of the two patients reported below, PPC level should have.reached the normal adult level. 7 Therefore, for
Submitted for publication March 21, 1988; accept~ed June 29, 1988. Reprint requests: Anne Dusser, MD, Unit6 Neurop6diatrie HSpital BicStre, 78, avenue du g6n6ral leclerc, 96270 Krem!in-BicStre, France.
the normal values of PPC antigen and activity, ranging from 0.70 to 1.30 U / m l (95% confidence interval), we referred to the values obtained in 100 healthy adults. CASE R E P O R T S Patient 1. A previously healthy 13-year-old white girl, an on!y child, suddenly developed a left-sided t?emiplegia with sensory I
PPC CT
Plasma protein C Computed tomography
I
impairment and hemianopsia. The CT scan showed a focal hypodensity in the internal part of the right occipital region and in the posteroinferior part of the right basal ganglia. Arteriography demonstrated a narrow and irregular caliber of the proximal portion of the right posterior cerebral artery and a reduced number of right posterior thalamoperforating branches. Biochemical and hemostatic tests were first performed 1 week after the stroke and were all within the normal range, with the exception of decreased PPC antigen (0.66 U/ml) and activity (0.63 U/ml) values while the patient was receiving no medications. The PPC level was decreased on four other determinations over a period of 8 months after the infarction (Figure). During this period; the patient was treated with 0.2 mg/kg/day of acetylsalicylic acid and half-month sequences of various drugs (levodopa, piribedil, febarbamate-phenobarbital, propran01ol), each administered alone to control a severe post-stroke dyskinesia. The PPC value spontaneously normalized approximately 1 year after the stroke (Figure). Protein C antigen and activity values were normal in the patient's father but decreased in her mother (ranging from 0.50 to 0.67 U/ml) on four different determinations performed within 1 year. Case 2. A previously healthy 2~2-year-old girl, of Malian origin
Cerebrovascular accidents in children with sickle-cell disease and alpha-thalassemia S c o t t T. Miller, MD, Ronald F. Rieder, MD, Sreedhar P. Rao, MD, a n d A u d r e y K. Brown, MD From the Department of Pediatrics, Divisionof Hematology/Oncology, and the Department of Medicine, Divisionof Hematology, State Universityof New York-Health Science Center at Brooklyn
Alpha-thalassemia occurs commonly in black Americans, ~ with approximately 30% lacking one a-glob{n gene (athai-2 genotype: aa/a-) and 4% lacking two genes (athai- 1 genotype: a - / a - or, rarely, aa/--). In individuals with sickle-cell disease, a-thalassemia attenuates some of the hematologic manifestations, 2-4 although the extent of clinical benefit remains controversial?. 5 Before routine implementation of long-term transfusion programs for children with sickle-cell disease and cerebrovascular accident, 6,7 CVA was ~i significant cause of death in the young sickle-cell disease population? Because the favorable effects of a-thalassemia on hematologic manifestations are apparent by the age of 1 year, 9 it is possible that a reduction in incidence of CVA, which occurs at a mean age of 7 years, s might contribute to prolonged survivaP in patients with sickle cell-a-thalassemia. In fact, a reduced incidence of a-thalassemia has been reported in a small group of patients with sickle-cell disease who have had a CVA? ~ The a-globin gene status of 20 of our sickle-cell disease patients with a history of CVA has been ascertained and is the basis for this report. METHODS
Subjects. All 20 patients with a history of CVA and currently receiving long-term transfusion therapy at this institution were studied. Median age of the patients at the time of diagnosis of CVA was 7 years (range 2 to 15 years), and all have been on a transfusion regimen to keep pretransfusion hemoglobin S levels <30% for 1 to 12 years (median 6 years); it is our current policy to continue transfusion indefinitely. Most patients receive transfusion of frozen-thawed deglycerolized packed red blood cells at 3-week intervals. All had clinical and laboratory values Submitted for publication May 2, 1988; accepted June 14, 1988. Reprint requests: Scott T. Miller, MD, SUNY-Health Science Center at Brooklyn, Department of Pediatrics, 450 Clarkson Ave., Box 49, Brooklyn, NY 11203.
compatible with the diagnosis of homozygous sickle-cell anemia before the institution of transfusion therapy. All had an acute onset of weakness of an extremity persisting at least 48 hours, with or without additional neurologic signs. Computed tomography scans done at an early stage in 17 of 20 patients (including all with a-thai-2) did not show intracranial hemorrhage. a-Gene analysis. Blood was obtained in calcium-ethylenediaminetetraacetic acid immediately before transfusion; DNA was prepared from the leukocytes. Aliquots were digested with restriction enzymes Bam HI and Bgl II and subjected to electrophoresis on agarose gel as previousCVA CT
Cerebrovascular accident Computed tomography
]
ly described. N After transfer to nitrocellulose paper, the blots were hybridized to a 32p-labeled a-complementary D N A probe and analyzed by autoradiography. RESULTS A single a-globin gene deletion (a-thai-2) was present in 5 of 20 (25%) patients; none had a-thai-1. The clinical and laboratory findings in these five patients with a-thai-2 sickle-cell disease are listed in the Table. Patient 5 was less anemic than is usual for patients with homozygous sicklecell disease; otherwise, a-thal-2 patients did not differ significantly from those with the normal allotment of a-globin genes. The a-thai-2 group included both our oldest and our youngest patients with CVA. Patient 1 had a CVA 4 months after completing 1 year of regular transfusion therapy for recurrent splenic sequestration; she underwent splenectomy at age 8 years after a sequestration episode that occurred during transfusion therapy. One patient in the non-a-thai group also has undergone splenectomy because of increased transfusion requirements and hypersplenism.
847
848
Clinical and laboratory observations
The Journal of Pediatrics November 1988
Table. Clinical and laboratory findings (before transfusion) in patients with sickle-cell disease, a-thai-2, and C V A Patient No. 1 2 3 4 5
Age at CVA (yr) 2V3 6 6 7 15
Neurologic findings
Hemoglobin (gm/dl)
MCV (fl)
Reticulocytes (%)
L hemiparesis R hemiparesis L hemiparesis R hemiparesis Convulsions, coma, quadriparesis
7.6 8.7 7.5 7.5 10.4
87 96 NA NA 91
13.7 11.7 15.0 9.5 6.5
MCV, Mean corpuscular volume;NA, not available.
DISCUSSION Cerebrovascular accidents in children with sickle-cell disease are most often due to stenotic or occlusive lesions of large or middle-caliber cerebral arteries. 7 These lesions are associated with intimal fibromuscular proliferation, perhaps as a result of damage to vascular endothelium by abnormal adherence of sickled cells. 7 Because c~-thalassemia-sickle cell patients have lower numbers of irreversibly sickled cells, 3 it was reasonable to postulate that endothelial damage may be less severe and thus that the risk of stroke may be diminished in this group of patients, particularly because the favorable influence of ~-thalassemia on various hematologic measurements is apparent at an early a g e ) Patients doubly heterozygous for sickle hemoglobin and either/3-thalassemia or hemoglobin C are at diminished risk for CVA, 12 although this protection is not absolute. 12,13 Twenty-five percent of our sickle-cell disease patients with C V A did, however, have concomitant c~-thal-2, a figure similar to that seen in the general American black population, l Patient characteristics were indistinguishable from those with the normal c~-globin genotype. No patients with C V A had c~-thal-1, although the small number of patients examined precludes suggesting that patients with a two-gene deletion may be protected from CVA. In a small group of pediatric patients with C V A reported by Piomelli et al., ~~c~-thal-1 patients were also not present; it may be that the more substantial improvement in hematologic values associated with c~-thal-12 will indeed be shown to exert a protective effect when larger numbers of patients are analyzed. Our data do not support the finding by Piomelli et al. that a single c~-gene deletion protects from stroke in sickle-cell anemia. One of our patients with c~-thal-2 had splenic sequestration episodes before her C V A and also subsequently, while on a long-term transfusion program. An association between c~-thalassemia and splenic sequestration was reported previouslyl4; however, sequestration in this patient was unexpected, because long-term transfusion therapy
has been recommended as an effective means of preventing recurrent sequestration in patients with homozygous sickle-cell disease who have had a sequestration episode. 15 It is possible that sickle cell-c~-thalassemia patients are for some reason less protected from sequestration by transfusion than are patients with sickle-cell disease who have a normal allotment of c~-globin genes. We thank Diane Jensen and Laurene Pollio for assistance in the clinical care of our patients.
REFERENCES
1. Dozy AM, Kan YW, Embury SH, et al. Alpha globin gene organization in blacks precludes the severe form of alphathalassemia. Nature 1979;280:605-7. 2. Embury SH, Dozy AM, Miller J, et al. Concurrent sickle cell anemia and cr N Engl J Med 1982;306:270-4. 3. Higgs DR, Aldridge BE, Lamb J, et al. The interaction of alpha-thalassemia and homozygous sickle-cell disease. N Engl J Med 1982;306:1441-6. 4. Steinberg MH, Rosenstock W, Coleman MB, et al. Effects of thalassemia and microcytosis on the hematologic and vasoocclusive severity of sickle cell anemia. Blood 1984;63:135360. 5. Mears G J, Laehman HM, Labie D, Nagel RL. Alphathalassemia is related to prolonged survival in sickle cell anemia. Blood 1983;62:286-90. 6. Sarnaik S, Soorya D, Kim J, et al. Periodic transfusions for sickle cell anemia and CNS infarction. Am J Dis Child 1979;133:1254-7. 7. Russell MO, Goldberg HI, Hodson A, et al. Effect of transfusion therapy on arteriographic abnormalities and on recurrence of stroke in sickle cell disease. Blood 1984;63: 162-9. 8. Powars DR, Wilson B, Imbus C, et al. The natural history of stroke in sickle cell disease. Am J Med 1978;65:461-71. 9. Stevens MCG, Maude GH, Beckford M, et al. Thalassemia and the hematology of homozygous sickle cell disease in childhood. Blood 1986;67:411-4. 10. Piomelli S, Seaman C, Cirella B, et al. Does alpha-thalassemia protect from early stroke in sickle cell anemia [Abstract]? Pediatr Res 1986;10:285A. 11. Safaya S, Multaney P, Rieder RF. Dysfunctional a-globin genes in hemoglobin H disease in blacks: variation in restric-
Volume 113 Number 5
tion fragment size permits the detection of the -c~/-c~v genotype. Am J Hematol 1987;26:329-39. 12. Sarnaik SA, Lusher JMi Neurological complications of sickle cell anemia. Am J Pediatr Hematol/Oncol 1982;4:386-94. 13. Fabian RH, Peters BH. Neurological complications of hemoglobin SC disease. Arch Neurol 1984i4h289-92. 14. Mears JG, Schoenbrun M, Schaefer KE, et al. Frequent
Clinical and laboratory observations
849
association of alpha-thalassemia with splenic sequestration crisis and splenomegaly in sickle cell subjects [Abstract]. Blood 1982;60(suppl 1):47a. 15. Rao S, Gooden S. Splenic sequestration in sickle cell disease: role of transfusion therapy. Am J Pediatr Hcmatol/Oncol 1985;7:298-301.
Interested readers may want to compare the older patients discussed in the following article with the neonates described by Manco-Johnson et al., in the August 1988 issue (J PEDIATR 1988;112:35963). -J.M.G.
Temporary protein C deficiency associated with cerebral arterial thrombosis in childhood Anne Dusser, MD, Catherine Boyer-Neumann, MD, and Martine Wolf From the Universit6 Paris-Sud, D~partement de P6diatrie, Unite de Neurop6diatrie and Laboratoire d'H6matologie, HOpital Bicetre, Kremlin-Bic~tre, France
Protein C in association with its cofactor protein S (both vitamin K-dependent plasma proteins) is a potent anticoagulant that regulates coagulation by inhibiting activated cofactors V and VIII C and by stimulating fibrinolysis. The association of recurrent venous thrombosis and hereditary protein C deficiency has been reported since 1981, ~4 suggesting the existence of a relationship between thrombosis and protein C deficiency. We report two observations of cerebral arterial thrombosis associated with a partial and temporary plasma protein C deficiency. METHODS Protein C antigen was measured by enzyme-linked immunosorbent assay, as described previously, s When the PPC antigen value was found to be decreased, PPC activity was also determined by a method based on the ability of activated protein C to prolong the activated partial thromboplastin time of normal plasma. 6 Protein C antigen and activity were expressed in units per milliliter, 1 unit being defined as the amount of protein C present in 1 ml of reference plasma, which was obtained from a pool of 25 healthy donors and stored at - 8 0 ~ C in small aliquots. At the ages of the two patients reported below, PPC level should have.reached the normal adult level. 7 Therefore, for
Submitted for publication March 21, 1988; accept~ed June 29, 1988. Reprint requests: Anne Dusser, MD, Unit6 Neurop6diatrie HSpital BicStre, 78, avenue du g6n6ral leclerc, 96270 Krem!in-BicStre, France.
the normal values of PPC antigen and activity, ranging from 0.70 to 1.30 U / m l (95% confidence interval), we referred to the values obtained in 100 healthy adults. CASE R E P O R T S Patient 1. A previously healthy 13-year-old white girl, an on!y child, suddenly developed a left-sided t?emiplegia with sensory I
PPC CT
Plasma protein C Computed tomography
I
impairment and hemianopsia. The CT scan showed a focal hypodensity in the internal part of the right occipital region and in the posteroinferior part of the right basal ganglia. Arteriography demonstrated a narrow and irregular caliber of the proximal portion of the right posterior cerebral artery and a reduced number of right posterior thalamoperforating branches. Biochemical and hemostatic tests were first performed 1 week after the stroke and were all within the normal range, with the exception of decreased PPC antigen (0.66 U/ml) and activity (0.63 U/ml) values while the patient was receiving no medications. The PPC level was decreased on four other determinations over a period of 8 months after the infarction (Figure). During this period; the patient was treated with 0.2 mg/kg/day of acetylsalicylic acid and half-month sequences of various drugs (levodopa, piribedil, febarbamate-phenobarbital, propran01ol), each administered alone to control a severe post-stroke dyskinesia. The PPC value spontaneously normalized approximately 1 year after the stroke (Figure). Protein C antigen and activity values were normal in the patient's father but decreased in her mother (ranging from 0.50 to 0.67 U/ml) on four different determinations performed within 1 year. Case 2. A previously healthy 2~2-year-old girl, of Malian origin