A large homozygous deletion in the SAMHD1 gene causes atypical AicardiaGoutiACOres syndrome associated with mtDNA deletions

AicardiaGoutiACOres syndrome (AGS) is a genetic neurodegenerative disorder with clinical symptoms mimicking a congenital viral infection. Five causative genes have been described: three prime repair exonuclease1 (TREX1), ribonucleases H2A, B and C, and most recently SAM domain and HD domain 1 (SAMHD1). We performed a detailed clinical and molecular characterization of a family with autosomal recessive neurodegenerative disorder showing white matter destruction and calcifications, presenting in utero and associated with multiple mtDNA deletions. A muscle biopsy was normal and did not show any evidence of respiratory chain dysfunction. Southern blot analysis of tissue from a living child and affected fetuses demonstrated multiple mtDNA deletions. Molecular analysis of genes involved in mtDNA synthesis and maintenance (POLGI-, POLGI2, Twinkle, ANT1, TK2, SUCLA1 and DGOUK) revealed normal sequences. Sequencing of TREX1 and ribonucleases H2A, B and C failed to reveal any mutations. Whole-genome homozygosity mapping revealed a candidate region containing the SAMHD1 gene. Sequencing of the gene in the affected child and two affected fetuses revealed a large deletion (9akb), spanning the promoter, exon1 and intron 1. The parents were found to be heterozygous for this deletion. The identification of a homozygous large deletion in the SAMHD1 gene causing atypical AGS with multiple mtDNA deletions may add information regarding the involvement of mitochondria in self-activation of innate immunity by cell intrinsic components.