Patients all have biallelic pathogenic mutations in the gene. Various mutations have been described. Most are missense mutations but also splice site mutations occur and deletions. A patient has been described with one pathogenic mutation and a deletion on the other allele. Diagnostic testing at the metabolite level should include lactate-, methylmalonic acid- and carnitine profiling (increased C4-dicarboxylic carnitine) in plasma and/or dry blood spot (DBS). Increased values are generally found. These parameters can also be abnormal in urine.