To analyze and summarize clinical phenotypes and genetic characteristics of children with rare disease mucolipidosis (ML).

Two patients (patient 1 and patient 2) diagnosed with ML at the National Children′s Medical Center, Children′s Hospital of Fudan University, between June 2016 and June 2023 were selected as the study subjects. A retrospective analysis of their clinical characteristics was conducted. Literature related to Chinese pediatric ML cases was searched in China National Knowledge Infrastructure (CNKI), Wanfang Data Knowledge Service Platform, and PubMed databases using the keywords " mucolipidosis" and " children" for the period from June 2013 to June 2023. The procedures followed in this study conformed to the standards set by the Ethics Committee of Children′s Hospital of Fudan University and were approved by the committee (Approval No. [2022] 241). Informed consent was obtained from the guardians of ML patients included in this study.

① Both patients were female, aged 1 year and 4 months, and 10 years, respectively, both exhibiting developmental delays and hand deformities or abnormalities. Whole exome sequencing (WES) revealed that patient 1 had a homozygous mutation in the GNPTAB gene, while patient 2 had compound heterozygous mutations in the GNPTG gene. Both sets of parents were heterozygous carriers. ②Based on the search strategy, 7 articles published by Chinese researchers were identified, involving 15 Chinese pediatric ML cases. Including the two patients from this study, a total of 17 cases were analyzed. Among the 17 patients, the male-to-female ratio was 1∶2.4, with an median age of 2.8 years (1.6-8.3 years), median height of 80.50 cm (76.45-123.00 cm), and median weight of 9.5 kg (8.6-26.0 kg). The distribution of different gene mutations was GNPTAB∶ GNPTG = 13∶4, and the mutation types was compound heterozygous∶homozygous = 9∶8. All 17 patients exhibited various degrees of clinical abnormalities as defined by the Human Phenotype Ontology (HPO), and patients with GNPTG mutations were older than those with GNPTAB mutations.

ML is a rare genetic metabolic disorder diagnosed mainly as ML type Ⅱ and Ⅲ in China, with mutations in the GNPTAB or GNPTG genes. Among these mutations, children with GNPTG gene variants tend to have a longer life expectancy than those with GNPTAB gene variants. Newborn genetic screening is helpful in identifying and intervening in ML at an early stage.