SAMHD1 mutations in LAA patients. Schematic representation of the 16-exon SAMHD1 gene (upper panel) and its 626-amino-acid gene product (lower panel). Sixteen exons encode a 626-amino-acid protein that comprises two structural domains. The SAM (sterile alpha motif) and HD (histidine-aspartate) domains are connected by a flexible linker. An oval indicates the location of a nuclear localisation signal. Locations of the missense (P22S, Q281K) and exon 6 splice donor (spl) mutations found in LAA patients are indicated.