Small chromosomal rearrangements may be behind idiopathic learning disability

Learning disability affects about 3% of the population, yet the cause remains unknown in about 40% of people with moderate to severe learning disability (IQ<50) and in 70% of people with mild developmental delay (IQ 50-75).1 It is estimated that between 30% and 50% of cases of undiagnosed learning disability may be genetic in origin.2 Mapping and sequencing the human genome have provided new ways of looking for chromosomal abnormalities. The standard investigation for learning disability is to stain chromosomes to reveal their unique banding pattern and then to look for any anomalies using light microscopy. However, the resolution of this routine cytogenetic approach is limited since very small rearrangements are not visible and larger abnormalities escape notice if they occur in regions where the banding pattern is not distinctive. There have been many attempts to increase …