This screening strategy was related to second-tier cystic fibrosis (CF) testing, which looks for two CFTR variants to minimize the referral of CF carriers for follow up.33 Of the 28 MMA patients, two patients (B2 and F4) had only a single P/LP variant, while one patient (F3) had only one VUS in a MMA gene (Supplementary Table 1). The gene discussed is CFTR; the disease is cystic fibrosis.