There are many kinds of genetic metabolic diseases, and the total number of diagnoses may exceed thousands. Although the prevalence rate of a certain type of IMD is low with the incidence rate from ten in thousands to hundreds in thousands, if all genetic metabolic diseases are added together, the overall prevalence rate will be higher than the above data[1].
4.1 Progress in the screening of Neonatal MS/MS genetic Metabolic Diseases
MS/MS technology has been used in the screening of neonatal genetic metabolic diseases since the early 1990s. By detecting the levels of multiple amino acids, free carnitine and acylcarnitine at the same time to screen the genetic metabolic diseases of oxidative disorders of amino acids, organic acids and fatty acids, the transformation from "one disease detected in one test" to "multiple diseases detected in one test" has been accomplished. In recent years, the National Clinical Laboratory Center has formulated and issued relevant consensus to ensure the standardization of the operation process from sample collection, laboratory testing, report interpretation, recall, diagnosis to treatment, as well as to the entire chain of follow-up management to ensure the quality of laboratory screening work in new screening centers across the country[5–7]. MS/MS technology is currently widely used in the screening of neonatal genetic metabolic disease screening due to its relatively low screening cost, high sensitivity (99%) and specificity (> 99.8%) [8]. Screening for genetic metabolic diseases of MS/MS newborns has been carried out in Huai'an since 2018, and the screening rate has increased year by year, from 21.15–99.53%. The recall rate of positive cases has also increased annually, from 88.64–97.96%. Our data fully showed that with the collaborative efforts of screening personnel, the screening of genetic metabolic diseases of newborns using MS/MS in Huai'an area is very effective, which has made significant contributions to the diagnosis, treatment and prevention of genetic metabolic diseases in the area.
4.2 Overall incidence and diagnosis of genetic metabolic diseases screened by MS/MS technique
At the moment, the majority of genetic metabolic diseases diagnosed using MS/MS screening technology at home and abroad are organic acids, amino acids and fatty acid metabolic diseases. There are great differences in neonatal genetic metabolic diseases and incidence reported in different countries or regions. About 40 kinds of diseases are screened in Italy, and the incidence rate is about 1 in 6041 [9]; there are 13 kinds of diseases screened in Spain with an incidence rate of about 1 in 2577 [10]. There are 24, 18 and 24 screening diseases in Germany, Japan and Korea, and the incidence rate is 1/2200, 1/8557 and 1/13205 respectively [11].Currently, there are more than 27–40 kinds of MS/MS genetic metabolic diseases that can be screened by the neonatal disease screening centers in various regions of China. In this study, a total of 97410 newborns were screened in Huai'an area, and 25 cases of genetic metabolic diseases were clinically diagnosed. The incidence rate is 1/3896, which is close to the average incidence rate of China (3.13/10,000) [12] and the Guangzhou area in Guangdong Province (1/3444), Shanghai area (1/3483) and Beijing area (1/3666) [13–15 ].Of note, the incidence rate in Huai’an area is significantly lower than that in Quanzhou area in Fujian Province(1/2826) [16], Jining area in Shandong Province (1/1941) [17],as well as Nanjing (1/2835) and Suzhou in Jiangsu Province (1/2910) [2,18].In addition, we found that the top three genetic metabolic diseases with the highest incidence in Huai’an area are phenylalanine hydroxylase deficiency, methylmalonic acidemia and primary carnitine deficiency, which was consistent with the domestic research report [12].
The 25 children in this study who were clinically diagnosed with genetic metabolic diseases were abnormal in different degrees and were still being identified by MS/MS, indicating that MS/MS is a reliable approach and plays an important role in the early screening and diagnosis of neonatal genetic metabolic diseases. Among the 25 children, only 21 cases were diagnosed by genetic analysis, as 4 cases dropped out due to refusing genetic testing. Thus, the rate of gene diagnosis was 84.00% which is expected to be improved. Gene detection can help parents to decide whether to give birth to a child with genetic metabolic diseases. Gene detection can help parents discover the gene mutations of children with genetic metabolic diseases and their parents. In addition, the gene test results can also help doctors to design individualized clinical treatments for diseased children. Therefore, we believe that genetic diagnosis should be performed for all children with genetic and metabolic diseases.
4.3 Prevalence and diagnosis of three kinds of genetic metabolic diseases
There are great differences in the prevalence of organic acids, amino acids and fatty acids among different countries, regions and races.
4.3.1 Amino acid metabolic disease
A study that included 246 cases of neonatal disease screening centers in China [19] showed that the average prevalence rate of amino acid metabolic disease was 17.14 / 100000, which was similar to that in Austria (1/4980)[20] and Portugal (1/5856) [21]. The prevalence rate of amino acid metabolic disease in Carolina in the United States was lower(1/25000)[22], and the prevalence in Europe (1/10000) [23] is in the middle. A total of 9 cases of two kinds of amino acid metabolic diseases were detected in Huai'an area. the prevalence rate is1/10823, which is similar to that of Zhejiang Province(1/11349)[24], Taiwan(1/11236)[25] and Europe but significantly lower than the national average level [19]. In this study, 8 cases of phenylalanine hydroxylase deficiency were diagnosed, and the prevalence rateis1/12176, which counts for the majority of amino acid metabolic diseases in this area. The prevalence was consistent with the China domestic research report which showed that the prevalence rate of phenylalanine hydroxylase deficiency in China is 1/(3000 ~ 16000), which is higher in the north than in the south【26】. The prevalence rates of phenylalanine hydroxylase deficiency in the Guangzhou area of Guangdong Province [14], Zhejiang Province [24], Jining area of Shandong Province [17] and Xinxiang area of Henan Province [27]were 1/30235, 1/22400, 1/9183 and 1/3341, respectively. The analysis of this data shows that the prevalence rate in Huai'an area is in line with the characteristics of "high in the north and low in the South". The lowest and highest values of serum phenylalanine and phenylalanine/tyrosine ratio in 8 patients with phenylalanine hydroxylase deficiency detected by MS/MS were 109.06 µ mol / L and 1870.4 µ mol / L, respectively. There were significant differences in serum phenylalanine concentration and ratio among different cases, which were related to the residual degree of phenylalanine hydroxylase activity. Among the 9 cases of the amino acid metabolic disease diagnosed clinically, one case of phenylalanine hydroxylase deficiency refused to do genetic testing. We found two inherited pathogenic mutations in PAH gene in7 cases of phenylalanine hydroxylase deficiency. Moreover, one of the phenylalanine hydroxylase deficiency subjects also has a heterozygous variation at a site of PTS gene, inherited from his mother. In addition, two mutations in MAT1A gene were found in 1 case of hypermethionemia, which was inherited from both parents.
4.3.2 Organic acid metabolic diseases
A total of 10 cases of six types of organic acid metabolic diseases were detected in this study. The overall incidence rate of six kinds of organic acid metabolic diseases is1/9741, which is slightly lower than the national average (12.39 / 100000) [19], Jining in Shandong Province(1/3956)[17] and Xinxiang in Henan Province ༈1/5568༉[27], but higher than Guangzhou in Guangdong Province ༈1/16007༉[13] and Zhejiang Province༈1/20200༉[28]. The prevalence of organic aciduria in Austria was1/13244, the most prevalent subtypes were 3-methylcrotonyl-CoA dehydrogenase deficiency (1/34583༉, glutaric acidemia type I ༈1/69165༉ and propionemia ༈1/77811༉[20]. The prevalence of organic acid metabolic disease in Carolina was1/16300. The most common diseases were 3-methylcrotonyl-CoA dehydrogenase deficiency (1/36000), methylmalonic acidemia(1/90000) and isovalerate acidemia (1/130000)[22]. Together, the above studies showed that there are significant differences in the disease spectrum of organic acid metabolic diseases in different countries. was Additionally, weidentified methylmalonic acidemia (1/24352) as the organic acid metabolism disease with the highest incidence which was comparable with the conclusion of multicenter research in China [19]. Among the 9 cases of organic acid metabolic disease that received genetic detection, two pathogenic mutations were found. In one case of the methylmalonic acidemia cases, we found not only a compound heterozygous mutation of MMACHC gene, but also a heterozygous mutation of one MUT gene and one heterozygous mutation of CD320 gene, respectively.
4.3.3 Fatty acid metabolism diseases
In this study, a total of 6 cases of three types of fatty acid metabolism diseases were detected in Huai'an area. The prevalence rate was 1/16235, which is significantly lower compared to the national average level in China (9.16 / 100000) [19]. Compared to other areas and countries, the prevalence of fatty acid metabolism diseases in Huai’an area is similar to that in Jining, Shandong Province (1/15125)[17] and Zhejiang Province (1/15382) [29], significantly lower than in Guangzhou area of Guangdong Province ༈1/6977༉[13], Quanzhou area of Fujian Province (1/7440) [16], Nanjing of Jiangsu Province (1/11718)[2], Suzhou area (1/10041) [18] and Shanxi Province (1/9015) [30], but higher than that of Japan (1/30000) and Korea (1/111000) [11]. Four cases of primary carnitine deficiency were detected, the prevalence rate of primary carnitine deficiency is1/24352 in this study, making it the most common disease of the 3 types of fatty acid metabolic diseases. This finding is consistent with the domestic research report 【12,19】. One case of short-chain and one case of medium chain acyl CoA dehydrogenase deficiency was diagnosed, and the prevalence rate for them is 1/97410.Intriguingly, 4 cases of maternal carnitine deficiency were detected. and the level of free carnitine in the corresponding child was lower than that in children with primary carnitine deficiency, which was supported by the results of Yiming Lin et. al. [31]Yiming Lin et. al. showed…..A possible explanation is that the free carnitine in the mother was transported to the fetus through the placenta [32]. Among the 4 children with fatty acid metabolic disease who had the genetic detection, two pathogenic mutation sites were found and the mutations were inherited from the parents.
4.4 Conclusion
Neonatal MS/MS genetic metabolic disease screening has become the mainstream screening method in the field of neonatal disease screening in the international community, which has greatly expanded the ability and capacity of disease screening in the medical care system. Since 2018, MS/MS neonatal genetic metabolic disease screening has been carried out in Huai’an area, and the work has achieved remarkable results. The screening rate and recall rate have increased year by year and have reached the ideal level. Among 97410 newborns in this area, 25 cases of 11 kinds of genetic metabolic diseases were detected. Given that the incidence of overall IMDs and single diseases in Huai’an area are both comparable to the national average, we believe that the neonatal MS/MS genetic metabolic disease screening system in Huai’an is successfully established. The diseased children were identified and most of them are diagnosed with common genetic metabolic diseases, which are preventable and treatable. The genetic diagnosis rate of children with genetic metabolic diseases in Huai'an area (84.00%) is low. Therefore, we should pay attention to the screening, diagnosis and treatment of neonatal genetic metabolic diseases, and do early screening, early diagnosis and early treatment to improve the quality of patient's life and reduce the burden on family and society. Based on the existing MS/MS genetic metabolic disease screening, further exploring the suitable and optimized screening techniques in this region is needed to reduce the incidence of birth defects, the disability of children with genetic metabolic diseases, and improve the quality of the population, provide a strong guarantee for the implementation of the two-child and three-child policy in our country.