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The need for these registries arose because, in the days prior to DNA parentage testing, the American Quarter Horse Association (AQHA) would not register horses with excessive white markings, sometimes called "cropouts", thinking that such markings were a sign of non-purebred breeding and was maintained for several decades because it was also feared that excess white increased the risk of horses producing a foal with lethal white syndrome (LWS).
Today, modern DNA testing has now made verification of parentage possible, and also permits the detection of certain genetic diseases such as lethal white syndrome.