Primary coenzyme Q10 (CoQ10) deficiency is usually associated with multisystem involvement, including neurologic manifestations such as fatal neonatal encephalopathy with hypotonia; a late-onset slowly progressive multiple-system atrophy-like phenotype (neurodegeneration with autonomic failure and various combinations of parkinsonism and cerebellar ataxia, and pyramidal dysfunction); and dystonia, spasticity, seizures, and intellectual disability. Steroid-resistant nephrotic syndrome (SRNS), the hallmark renal manifestation, is often the initial manifestation either as isolated renal involvement that progresses to end-stage renal disease (ESRD), or associated with encephalopathy (seizures, stroke-like episodes, severe neurologic impairment) resulting in early death. Hypertrophic cardiomyopathy (HCM), retinopathy or optic atrophy, and sensorineural hearing loss can also be seen.

Pseudo-TORCH syndrome-2 (PTORCH2) is an autosomal recessive multisystem disorder characterized by antenatal onset of intracranial hemorrhage, calcification, brain malformations, liver dysfunction, and often thrombocytopenia. Affected individuals tend to have respiratory insufficiency and seizures, and die in infancy. The phenotype resembles the sequelae of intrauterine infection, but there is no evidence of an infectious agent. The disorder results from inappropriate activation of the interferon (IFN) immunologic pathway (summary by Meuwissen et al., 2016). For a discussion of genetic heterogeneity of PTORCH, see PTORCH1 (251290).