MCCC2 and Isolated 3-methylcrotonyl-CoA carboxylase deficiency: Given the maximum AF of 3.2% for this MCCC2 variant in the cohort and the existence of 3 homozygous carriers with no matching clinical symptoms, the pathogenicity of this variant cannot be confirmed as it is common to find homozygous individuals who are asymptomatic due to the phenotypic variability of MCC deficiency.