[Analysis of the regional distribution differences of common variations of the MMACHC gene in cblC methylmalonic acidemia patients].

To analyze regional differences in MMACHC gene variations among patients with cblC-type methylmalonic acidemia (MMA) in China and to explore the relationship between these variations and neonatal screening, biochemical markers and prognosis. Retrospective case summary. Clinical and laboratory data, including general condition, biochemical markers and genetic analysis, were collected from 1 859 cblC MMA patients from 2005 to 2023. Patients were divided into 7 groups according to their regions: north China, northeast China, east China, central China, south China, southwest China and northwest China. They were also classified into neonatal screening and non-neonatal screening groups. Mann-Whitney and Kruskal-Wallis tests were used to compare biochemical marker levels. In contrast, the Chi-square test was applied to compare MMACHC gene variant frequencies, neonatal screening proportion, onset age and prognosis between groups. Among 1 859 cases of cblC MMA, 1 019 were male and 840 were female, with a consultation age of 1.0 (0.1, 5.0) month. A total of 1 787 cases carried compound heterozygous or homozygous variants and only 1 variant site was identified in 72 cases. The 10 most frequent variants were c.609G>A (1 238 cases), c.658_660delAAG (343 cases), c.80A>G (284 cases), c.482G>A (239 cases), c.567dupT (191 cases), c.656_658delAGA (131 cases), c.217C>T (109 cases), c.394C>T (105 cases), c.445_446delTG (51 cases) and c.1A>G (50 cases). The frequency of the c.609G>A was the lowest in northwest China (28.8% (44/154), ²=-18.42, <0.05). The frequency of the c.567dupT was the most common in southwest China (25.0% (20/80), ²=71.70, <0.001) and c.656_658delAGA had the highest frequency in northeast China (9.3% (19/205), ²=32.08, <0.001). Non-missense variants (91.2% (62/68), 88.5% (46/52)) and early-onset patients (90.0% (36/40), 94.4% (34/36)) were both more prevalent in southwest and south China (²=14.95, 31.69, both <0.05). The proportion of neonatal screening was the lowest in south China (22.2% (8/36), ²=98.48, <0.05), where the mortality rate was the highest (19.1% (4/21), ²=38.98, <0.001). East China exhibited the highest frequency of missense variants (21.5% (339/1 579)), the highest proportion of patients identified through neonatal screening (54.5% (465/853)), and a more significant proportion of patients with good prognosis (36.6% (227/621), ²=14.57, 93.49, 38.98, all <0.05). In addition, the c.482G>A variant was more frequent in patients diagnosed by neonatal screening compared to those diagnosed by other methods (8.3% (132/1 586) 5.9% (122/2 060), ²=7.97, <0.05). The frequency of MMACHC gene variation varies across different regions. The c.609G>A was least frequent in northwest China, c.567dupT was most common in southwest China, and c.656_658delAGA was most prevalent in northeast China. South China had the lowest neonatal screening rate and the highest mortality. At the same time, east China exhibited the highest frequency of missense variants, the highest proportion of patients identified through neonatal screening and the best prognosis. The c.482G>A variant was more frequent in patients diagnosed by neonatal screening compared to those diagnosed by other methods.