GNAS and Alzheimer disease: Following the initial discovery of a recurrent chromosomal microdeletion affecting the STX16 gene locus in autosomal dominant–PHP1B (AD-PHP1B) kindreds (9), various genetic alterations have been identified in other patients with AD-PHP1B: chromosomal deletions involving the NESP55 exon and/or AS exons 3/4, chromosomal duplications, a chromosomal inversion, and retrotransposon insertions (5, 10–15).