In this study, 225 patients with MPS and 209 normal newborns were finally included in the statistics. According to statistics, delayed diagnosis of MPS was common in China, the average age of diagnosis was 4.44 years old(median age of diagnosis = 3 years old), with 48.89% of patients diagnosed at ≥ 4 years old. According to literature reports, from 1985 to 2019, the median diagnosis age of MPS patients in the Taiwan area was 3.9 years. Compared to our study, the median diagnosis age was later. Considering that it may be related to the limitations of gene testing and enzyme activity testing techniques in the Taiwan area before the 21st century18. Because some symptoms were progressive and irreversible, and the smaller the age had a better curative effect on treatment, early diagnosis and treatment were very important for the prognosis and future life quality of MPS patients19–21. With the progress of diagnostic technology in our country, the situation of delayed diagnosis or misdiagnosis was gradually improving. Therefore, we considered that if Mongolian spots were feasible for early screening of MPS, it would be of great significance for diagnosis and treatment.
In study, the incidence of Mongolian spots in MPS Ⅱ was the highest (92.39%) among different types, which was consistent with the literature reported17,22, followed by MPS Ⅰ, and MPS Ⅳ was the lowest. We found that the incidence of Mongolian spots with greater than or equal to 2 in MPS Ⅵ patients with Mongolian spots was the highest (91.67%), followed by MPS Ⅱ, and MPS Ⅶ was the lowest. For the incidence of Mongolian spots with greater than or equal to 5, MPS Ⅰ was the highest (70.59%), followed by MPS Ⅱ, and MPS Ⅳ was the lowest. We boldly concluded that the extensive Mongolian spots played a significant role in MPS Ⅰ, Ⅱ and Ⅵ, but not for MPS Ⅲ, Ⅳ or Ⅶ. According to our statistics, Mongolian spots in MPS (73.78%) were slightly higher than that in normal neonates (66.51%) with a margin difference. Moreover, the mean number of Mongolian spots in MPS was higher than that in normal neonates. the incidence of Mongolian spot numbers ≥ 2 and ≥ 5 was both significantly different between MPS patients and normal newborns. After all consideration, it was suggested that the number of Mongolian spots ≥ 4 could be useful for early screening. Hence, we considered that multiple Mongolian spots were an important symptom of MPS, which could be used for early screening and was helpful for the detection of MPS. It was obvious that the length of Mongolian spots in MPS group was greater than control group.
Moreover, we found that the more Mongolian spots in children, the earlier the diagnosis age. For one thing, it could be speculated that the more the number of Mongolian spots in children, the more severe the clinical symptoms may be, which attracts the attention of doctors and parents. For another, the extensive Mongolian spots play a guiding role in clinical diagnosis, making it easy for some pediatricians to associate with MPS. According to the data analysis, the distribution of Mongolian spots in normal children was relatively limited. However, it was widely distributed in MPS patients comparatively. Statistically, it was found that the proportion of Mongolian spots regression in MPS was lower than that in normal children comparing literature reports11,15,17,23. Combined with the literature reports, it can be hypothesized that metabolic abnormalities in MPS may hinder the regression of Mongolian spots13,15,17,24−26.
Our research did exist some shortcomings. First, among the patients we collected, due to the different incidence rates of different types, the number of patients such as MPS Ⅲ and MPS Ⅶ was relatively small. Second, MPS patients recruited from all over the country and took the form of a telephone survey, errors and recall bias may occur. Moreover, some patients were lost in the late stage of the investigation, resulting in missing some data, which led to the failure of some patients to be included in the study. What’s more, our study lacked long-term follow-up observation in control group.
In conclusion, this study showed that extensive Mongolian spots have positive significance for early screening and early diagnosis of MPS. Pediatricians should be alert to the occurrence of this symptom. When extensive and large Mongolian spots were discovered, it was suggested to improve urinary GAGs screen or close follow-up.