New techniques in molecular biology continue to provide fundamental knowledge about certain neurological disorders. Most notable is the demonstration in a number of pedigrees of the gene for familial Alzheimer's disease on chromosome 21.1 This chromosome has been under suspicion because of the Alzheimer-like changes seen in the brains of patients dying with Down's syndrome, most of whom had trisomy 21. As yet, the chromosomal localization to 21 has been demonstrated in a small number of families. However, similarly cautious claims were originally made about the localization on chromosome 4 of the genetic locus for Huntington's disease, but this has now been confirmed in dozens of pedigrees. It is likely that the same will occur with familial Alzheimer's disease.
Even more intriguing is the linkage between the locus for familial Alzheimer's disease and that for the amyloid protein seen in patients with Alzheimer's disease and with Down's syndrome.2