Loss of function in CIAO1, a key component of the cytoplasmic iron-sulfur cluster assembly (CIA) complex, has recently been linked by our group and others to a novel neuromuscular disorder and a lethal neurodegenerative phenotype, with clinical severity reflecting the extent of functional disruption caused by the reported variants. In this study, we expand the clinical and biochemical understanding of CIAO1-related disease by analyzing a larger cohort of affected individuals (n=12) and characterizing reported and newly identified disease-causing variants (n=9). Our cohort consists of 5 males and 7 females from 10 families, median age of 16.5 years, (range: 4-60 years) and includes two patients with novel homozygous genotypes: c.817G>C, p.(Asp273His) presenting with childhood-onset limb-girdle muscular dystrophy (LGMD) without CNS or systemic involvement, and c.645C>A, p.(Asp215Glu) presenting at one year with global developmental delay and muscle weakness and death at age 4 years following a respiratory infection. Biallelic c.905A>C, p.(His302Pro) in trans with c.193C>T, p.(Arg65Trp) has now been identified in eight individuals as a recurrent genotype. It is associated with a phenotypic spectrum of muscle and neurobehavioral symptoms, with an age of onset ranging from birth to 15 years. Four of the eight patients show clinical features compatible with autism spectrum disorder, while the remaining four reported academic and/or cognitive difficulties. Notably, increased iron deposition in the brain deep nuclei has been observed in 5 patients.
Functional characterization of the variants revealed a strong correlation between the turnover rates of the mutated proteins and the severity of clinical features. Collectively, our study defines the clinical and biochemical landscape of the newly defined CIAO1-related disorder and advances our understanding of how CIA loss of function leads to multisystem manifestations, with predominant neuromuscular involvement.