Light microscopic presentation of a normal, human male chromosome set (karyogram). The 46 chromosomes are stained and ordered by size and shape. The characteristic stripe pattern (banding pattern) allows exact assignment.
Conventional karyotyping refers to the light microscopic presentation of the chromosome set of a given cell. This set contains the genetic information and therefore the instruction for body plan and function. Loss or gain of chromosomal regions is detectable in about 15% of persons with mental retardation. The resolution of conventional karyotyping is limited. Therefore, many smaller aberrations leading to more or less pronounced mental retardation are not detectable. For this reason, several methods for molecular karyotyping were developed in the last years. Chromosomes are scanned for a minimum of loss or gain using thousands of molecular probes attached to arrays. Since the resolution is dependent on the number of probes, MRNET uses only the latest generation of high resolution arrays. In comparison to conventional karyotyping, the resolution is 10 to 100 fold better. Using this technique, small disease causing chromosomal aberrations can be detected in further 10-20% of persons with unexplained mental retardation.
Molecular karyogram. Besides the chromosome schemes the copy number which was determined by several thousands of measuring points, is shown. The example shows a deviation on chromosome 8 from the basis line to the right. This indicates a loss of chromosomal material in this region (partial monosomy 8q).