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Chromosome test

Very rarely, learning difficulties may be associated with a defect on the chromosomes. These are tiny, rod-shaped structures that carry the genes. They are present in every cell of the body. Abnormalities of the chromosomes, such as extra or missing chromosomal material, may affect the way the brain is formed and the way it functions.

To examine the chromosomes, a small amount of blood is collected and cultured for a few days in the laboratory. The blood sample is then processed and stained with dye so that the chromosomes can be seen under the microscope.

Abnormalities of the chromosomes are so infrequently found in children with learning difficulties who are of normal intelligence that this test is only performed if the paediatrician finds some indication from the history or physical examination that a chromosomal abnormality is likely to be present.

Electroencephalogram (EEG)

This is a test where the electrical activity normally present in the brain is measured. A special fabric cap is placed on the child’s head. The cap has wires connected to a machine that records the brain’s electricity in the form of a tracing on paper.

An EEG is a useful test if it is suspected that the child is performing poorly at school because of ‘petit mal’ epilepsy. This is a condition characterized by repeated episodes where the child goes blank for a moment, and so misses what is being said. Although petit mal epilepsy is often thought of, it is a very rare cause of learning difficulty. Most children who have blank episodes are simply day-dreaming, or voluntarily ignoring something they do not want to hear.

The paediatrician will arrange an EEG if he or she thinks that the story is suggestive of petit mal epilepsy. In other cases of children with learning difficulties, the EEG is generally unhelpful. Slightly abnormal tracings on EEG are quite common and of no practical importance.

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