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Volume 6 Issue 124 Published - 14:00 UTC 08:00 EST 3-May-2004 Next Update - 14:00 UTC 08:00 EST 4-May-2004
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Sickle cell disease produces silent strokes

Children and adolescents with a common variety of sickle cell disease may appear neurologically normal, but many are revealed to have suffered "silent" strokes or to have circulatory system abnormalities that put them at risk for overt strokes, according to a study published 3 May 2004, in the on-line edition of the Annals of Neurology.

According to the authors, the implications of the study are clear. "All sickle beta-thalassemia patients should be routinely screened with MRI and tests of brain blood flow in order to detect abnormalities not easily seen in clinical examination," said lead author Dimitrios I. Zafeiriou, MD, PhD, of the Aristotle University of Thessaloniki, Greece.

Sickle beta-thalassemia (or S-beta-thalassemia) is the unfortunate overlap of two distinct hereditary anemias -- sickle cell disease and thalassemia, also known as Cooley's anemia. Thalassemia, though not as well known as sickle cell disease in the United States, is in fact the most common, inherited single gene disorder in the world.

Sickle cell disease by itself has a relatively simple genetic and clinical picture: If you inherit the disease gene from one parent, you will have mild or no symptoms; if you inherit copies of the gene from both parents, you will have the disease, in which blood cells adopt abnormal shapes and are less robust. When the cells break down, organs all over the body can suffer damage from lack of oxygen.

Thalassemia, by contrast, has many gradations, ranging from no apparent symptoms to conditions that can cause severe birth defects. The type and number of genetic mutations determine the clinical picture.

Thalassemia is most prevalent in people of Greek, Italian, or other Mediterranean heritage. Sickle cell disease affects primarily people of African origin, though the disease causing genes are present in many people of Mediterranean origin.

The cruel irony is that many people with S-beta-thalassemia have inherited genes for sickle cell disease and thalassemia that should expose them to nothing worse than the mild versions of each disorder. Instead, they suffer the additive effects of different disruptions in the blood's ability to carry oxygen to the organs of the body.

Stroke is a well-known consequence of sickle cell disease, but patients with S-beta-thalassemia typically show no overt signs of stroke, nor do they show any mental deterioration that might point to undetected "silent" strokes.

Zafeiriou and his colleagues performed extensive testing on a group of 21 children and young adults with S-beta-thalassemia, including magnetic resonance imaging (MRI) and other tests to probe for brain abnormalities. They also used magnetic resonance angiography (MRA) and trans-cranial Doppler (TCD) testing to assess blood flow to the brain. Finally they used neuropsychological tests to determine if the subjects had experienced deficits in cognitive ability.

Although the patients did not show significant deficits on the neuropsychological testing, more than a third (38 percent) showed MRI evidence of previous silent strokes. Similarly, nearly a third of the patients tested, including many who had not had silent strokes, exhibited abnormal blood flow to the brain on MCA and/or TCD testing.

"The next step will be to follow these patients in order to see if they will experience clinically overt stroke," said Zafeiriou.

The authors would also like to know if factors such as diet might increase or decrease the risk of strokes. "If certain criteria for abnormality -- especially in transcranial Doppler -- are established from larger studies, then protocols for therapeutic intervention in order to prevent nervous system damage could be initiated," said Zafeiriou.


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