>>39554669>literal autismis still not recognized internationally.
A small number of scientists believe that autistic children appear to have a rare "double phenotype", resulting from an "autistic phenotype plus an autistic phenotype" (Kirp, 1989). They say that while there are hundreds of genes known to be involved in autism, most of them remain a puzzle of unknown function to scientists (Dutton, 2000). This phenomenon is called a "gene knock-out problem" because, although it is thought that autism is caused by defects in specific genes (see also Kurzweil et al (1997)). There are currently no known methods for identifying individuals who have a defective allele or a "gene knock-out defect" on their chromosomes. As a result, it is unknown how autism is actually contracted in children and this cannot be established without knowing whether the autism can be identified before and after it develops. Thus, this phenomenon has been termed by neuroscientists as a "gene knock-out problem".
In contrast, it is generally considered that any condition that causes a decrease in brain volume and consequently reduces brain size, thus increasing the risk of developing Alzheimer's disease, is caused by a defect in a specific gene. The mechanism for this is not exactly clear but the genetic cause appears to lie in a disruption of a protein that functions as a cell membrane, and thus appears to
