The mitochondrial genome as a modifier of autism versus cancer phenotypes in hamartoma tumor syndrome.

Cancer and autism spectrum disorder/developmental delay (ASD/DD) are two common clinical phenotypes in individuals with germline variants ( hamartoma tumor syndrome, PHTS). Burgeoning studies have shown that genomic and metabolomic factors may act as modifiers of ASD/DD versus cancer in PHTS. Recently, we showed copy number variations to be associated with ASD/DD versus cancer in these PHTS individuals. We also found that mitochondrial complex II variants occurring in 10% of PHTS individuals modify breast cancer risk and thyroid cancer histology. These studies suggest that mitochondrial pathways could act as important factors in PHTS phenotype development. However, the mitochondrial genome (mtDNA) has never been systematically studied in PHTS. We therefore investigated the mtDNA landscape extracted from whole-genome sequencing data from 498 PHTS individuals, including 164 with ASD/DD (PHTS-onlyASD/DD), 184 with cancer (PHTS-onlyCancer), 132 with neither ASD/DD nor cancer (PHTS-neither), and 18 with both ASD/DD and cancer (PHTS-ASDCancer). We demonstrate that PHTS-onlyASD/DD has significantly higher mtDNA copy number than PHTS-onlyCancer group (p = 9.2 × 10 in all samples; p = 4.2 × 10 in the H haplogroup). PHTS-neither group has significantly higher mtDNA variant burden than PHTS-ASDCancer group (p = 4.6 × 10); the PHTS-noCancer group (PHTS-onlyASD/DD and PHTS-neither groups) also shows higher variant burden than the PHTS-Cancer group (PHTS-onlyCancer and PHTS-ASD/Cancer groups; p = 3.3 × 10). Our study implicates the mtDNA as a modifier of ASD/DD versus cancer phenotype development in PHTS.