DataSheet1_Dissecting the multifaceted contribution of the mitochondrial genome to autism spectrum disorder.docx

Autism spectrum disorder (ASD) is a clinically heterogeneous class of neurodevelopmental conditions with a strong, albeit complex, genetic basis. The genetic architecture of ASD includes different genetic models, from monogenic transmission at one end, to polygenic risk given by thousands of common variants with small effects at the other end. The mitochondrial DNA (mtDNA) was also proposed as a genetic modifier for ASD, mostly focusing on maternal mtDNA, since the paternal mitogenome is not transmitted to offspring. We extensively studied the potential contribution of mtDNA in ASD pathogenesis and risk through deep next generation sequencing and quantitative PCR in a cohort of 98 families. While the maternally-inherited mtDNA did not seem to predispose to ASD, neither for haplogroups nor for the presence of pathogenic mutations, an unexpected influence of paternal mtDNA, apparently centered on haplogroup U, came from the Italian families extrapolated from the test cohort (n = 74) when compared to the control population. However, this result was not replicated in an independent Italian cohort of 127 families and it is likely due to the elevated paternal age at time of conception. In addition, ASD probands showed a reduced mtDNA content when compared to their unaffected siblings. Multivariable regression analyses indicated that variants with 15%–5% heteroplasmy in probands are associated to a greater severity of ASD based on ADOS-2 criteria, whereas paternal super-haplogroups H and JT were associated with milder phenotypes. In conclusion, our results suggest that the mtDNA impacts on ASD, significantly modifying the phenotypic expression in the Italian population. The unexpected finding of protection induced by paternal mitogenome in term of severity may derive from a role of mtDNA in influencing the accumulation of nuclear de novo mutations or epigenetic alterations in fathers’ germinal cells, affecting the neurodevelopment in the offspring. This result remains preliminary and needs further confirmation in independent cohorts of larger size. If confirmed, it potentially opens a different perspective on how paternal non-inherited mtDNA may predispose or modulate other complex diseases.

自闭症谱系障碍（ASD）是一类临床异质性神经发育障碍，虽致病机制复杂，但具有显著的遗传基础。自闭症谱系障碍的遗传结构涵盖多种遗传模式：一端为单基因遗传，另一端则是由数千个效应微弱的常见变异共同构成的多基因风险。线粒体DNA（mtDNA）也被提出可作为自闭症谱系障碍的遗传修饰因子，相关研究多聚焦于母源性mtDNA，因为父源性线粒体基因组不会传递给子代。我们依托98个家系队列，通过深度二代测序与定量PCR技术，系统探究了mtDNA在自闭症谱系障碍发病机制与患病风险中的潜在作用。尽管母源性mtDNA无论是单倍群类型还是致病性突变携带情况，均未表现出自闭症谱系障碍易感倾向，但在与对照人群的对比分析中，从测试队列（n = 74）中抽取的意大利家系数据显示，父源性mtDNA存在未预期的影响，且该影响似乎集中于单倍群U。然而，这一结果在127个家系的独立意大利队列中未得到重复，其原因可能与受孕时父亲的高龄有关。此外，自闭症谱系障碍先证者的mtDNA含量较其未受累同胞更低。多变量回归分析显示，在先证者中，携带15%~5%异质性比例的变异与基于ADOS-2标准评估的自闭症谱系障碍严重程度升高显著相关；而父源性超级单倍群H与JT则与较轻的表型相关。综上，我们的研究结果表明，mtDNA可对自闭症谱系障碍产生影响，并在意大利人群中显著改变其表型表达。父源性线粒体基因组在疾病严重程度方面所展现的未预期保护效应，可能源于mtDNA通过影响父亲生殖细胞中细胞核新发突变的积累或表观遗传修饰，进而对子代神经发育产生作用。该结果仍属初步结论，需在更大规模的独立队列中进一步验证。若该结论得到验证，则可能为探究父源性非遗传mtDNA如何易感或调控其他复杂疾病提供全新视角。