The clinical data and genetic characteristics of one child with mental retardation-56 (MRD56) diagnosed at the Department of Neonatology, Foshan Fosun Chancheng Hospital in October 2021 were retrospectively analyzed.The patient was admitted to the hospital with " 34 + 2 weeks of preterm birth, shortness of breath, and dyspnea for 0.5 hours". In the neonatal period, the patient had special facial features, hypotonia, weaning and feeding difficulties, laryngeal stridor.In infancy, the patient showed global psychomotor development delay, intellectual disability, epilepsy, etc.Magnetic resonance imaging of the brain showed delayed myelination and dysplasia of the cerebellum and corpus callosum.Whole-exome sequencing showed that the CLTC gene had a new missense mutation c.3334T>C (p.Trp1112Arg), and MRD56 was confirmed.A total of 32 cases of MRD56 were reported worldwide, with special facial features, intellectual disability, and psychomotor retardation as the main clinical manifestations.The cause is a mutation in the CLTC gene, which leads to abnormality in the structure of the clathrin encoded, thus affecting neurotransmitter transmission.This is the first report of MRD56 caused by the CLTC gene mutation in China, and a new clinical phenotype has been discovered.The finding enriches the phenotypic spectrum of the disease and provides a basis for clinicians to understand and study the disease.

The clinical data and genetic characteristics of one child with mental retardation-56 (MRD56) diagnosed at the Department of Neonatology, Foshan Fosun Chancheng Hospital in October 2021 were retrospectively analyzed.The patient was admitted to the hospital with " 34 + 2 weeks of preterm birth, shortness of breath, and dyspnea for 0.5 hours". In the neonatal period, the patient had special facial features, hypotonia, weaning and feeding difficulties, laryngeal stridor.In infancy, the patient showed global psychomotor development delay, intellectual disability, epilepsy, etc.Magnetic resonance imaging of the brain showed delayed myelination and dysplasia of the cerebellum and corpus callosum.Whole-exome sequencing showed that the CLTC gene had a new missense mutation c.3334T>C (p.Trp1112Arg), and MRD56 was confirmed.A total of 32 cases of MRD56 were reported worldwide, with special facial features, intellectual disability, and psychomotor retardation as the main clinical manifestations.The cause is a mutation in the CLTC gene, which leads to abnormality in the structure of the clathrin encoded, thus affecting neurotransmitter transmission.This is the first report of MRD56 caused by the CLTC gene mutation in China, and a new clinical phenotype has been discovered.The finding enriches the phenotypic spectrum of the disease and provides a basis for clinicians to understand and study the disease.