Improving the diagnosis of cobalamin and related defects by genomic analysis, plus functional and structural assessment of novel variants

A Review of Disparities and Unmet Newborn Screening Needs over 33 Years in a Cohort of Mexican Patients with Inborn Errors of Intermediary Metabolism

Advances in an early diagnosis by expanded newborn screening (NBS) have been achieved mainly in developed countries, while populations of middle- and low-income countries have poor access, leading to disparities. Expanded NBS in Mexico is not mandatory. Herein, we present an overview of the differences and unmet NBS needs of a group of Mexican patients with inborn errors of intermediary metabolism (IEiM), emphasizing the odyssey experienced to reach a diagnosis. We conducted a retrospective observational study of a historical cohort of patients with IEiM from a national reference center. A total of 924 patients with IEiM were included. Although 72.5% of the diseases identified are detectable by expanded NBS, only 35.4% of the patients were screened. The mortality in the unscreened group was almost two-fold higher than that in the screened group. Patients experienced a median diagnostic delay of 4 months, which is unacceptably long considering that to prevent disability and death, these disorders must be treated in the first days of life. Patients had to travel long distances to our reference center, contributing to their unacceptable diagnostic odyssey. This study highlights the urgent need to have an updated, expanded NBS program with adequate follow up in Mexico and promote the creation of regional medical care centers. We also provide compelling evidence that could prove valuable to decision makers overseeing public health initiatives for individuals impacted by IEiM from middle- and low-income countries.

Combined Malonic and Methylmalonic Aciduria Due to ACSF3 Variants Results in Benign Clinical Course in Three Chinese Patients

Introduction: Combined malonic and methylmalonic aciduria (CMAMMA) is a rare metabolic disease caused by biallelic variants in ACSF3 gene. The clinical phenotype is highly heterogeneous in this disorder, ranging from asymptomatic to severe symptoms. No cases with CMAMMA were reported in China. Materials and Methods: In this study, three Chinese pediatric patients were diagnosed with CMAMMA unexpectedly while being treated for other ailments. To better characterize CMAMMA in a Chinese population, we made a multidimensional analysis with detailed clinical phenotype, semi-quantitative detection of urine organic acid, and analysis of ACSF3 gene variants. Results: The clinical presentation of these patients is quite different; their main complaints were anemia, jaundice, or abnormal urine test, respectively. They showed no symptoms of the classic methylmalonic academia, but urine organic acid analysis showed elevated malonic acid and methylmalonic acid in all the patients repeatedly. Variants were found at four sites in ACSF3 gene. Patient 1 carried the compound heterogeneous variant c.689G> A (p.Trp230^*)/c.1456G> A (p.Ala486Thr). A compound heterozygous variant c.473C> T (p.Pro158Leu)/c.1456G> A (p.Ala486Thr) was identified in patient 2. Patient 3 harbored a novel homozygous variant c.1447A> G (p.Lys483Glu). Conclusions: Three Chinese patients were diagnosed with CMAMMA caused by ACSF3 variants. Their clinical course revealed that CMAMMA can be a benign condition that does not affect individual growth and development, but severe clinical phenotype may appear when other triggers exist. This study systematically elaborates CMAMMA in a Chinese population for the first time, broadens the spectrum of gene variant, and provides a strong basis for the etiological study of this disorder.