Background: ACAN (OMIM 155760) is located on chromosome 15q26 and encodes the production of aggrecan. Aggrecan is a large chondroitin sulfate proteoglycan with a molecular weight of 254 kDa and contains 2530 amino acids. It is a critical structural component of the extracellular matrix of cartilage, including growth plate, articular, and intervertebral disk cartilage. It plays a key role in bone development.Methods: Here, we describe two pedigrees with loss‐of‐function variants in ACAN. Whole exome sequencing was performed for the probands from each family. We illustrate the clinical variability associated with ACAN variants.Results: The proband of pedigree A manifested short stature, relative macrocephaly, mild flat nasal bridge, low‐set ears, short neck, and short thumbs. The proband of pedigree B had short height, abnormal vertebral development, and central precocious puberty. By trio‐based whole exome sequencing and in silico analyses, we identified two de novo heterozygous variants of ACAN: NM_013227.4: c.116dupT, p.Arg40Glufs*51 and NM_013227.4: c.2367delC, p.Ser790Glnfs*20 (accession number: AC103982.10).Conclusion: The clinical manifestations of ACAN gene variants are diverse. ACAN gene variants are important genetic factors for short stature and should be considered as the differential diagnosis of children with idiopathic short stature (ISS).

Background/Objectives: Chlamydia trachomatis (C. trachomatis) is an important cause of community-acquired pneumonia in early infancy; however, its subtle and nonspecific clinical features often result in underdiagnosis and delayed treatment. Evidence regarding clinical predictors of severe disease and distinctive imaging manifestations remains limited. This study aimed to characterize the clinical and imaging features of hospitalized infantile C. trachomatis pneumonia and to identify potential indicators associated with disease severity. Methods: This retrospective study enrolled infants with confirmed C. trachomatis pneumonia hospitalized at Beijing Children’s Hospital from January 2016 to December 2025. Data on demographics, clinical presentations, laboratory findings, chest imaging, treatments, and outcomes were systematically collected. Exploratory subgroup analyses were performed to compare severe and non-severe cases and identify severity-associated factors. Results: A total of 30 infants (16 boys, 14 girls) were included, with a median age of 34.0 days (IQR, 23.5–39.8 days) at symptom onset. Cough was nearly universal (96.7%), while fever, tachypnea, and wheezing were observed in 43.3%, 43.3%, and 40.0%, respectively. Pulmonary crackles were present in 86.7%, and eosinophilia in 40.0%. Cytomegalovirus co-infection occurred in 36.7%. Chest CT revealed patchy opacities (100%), interstitial changes (86.7%), mass-like/nodular opacities (63.3%), and diffuse miliary/granular opacities (13.3%). Among 14 patients undergoing bronchoscopy, 50.0% had thick airway secretions. Tachypnea and retractions emerged as important clinical indicators of severe disease. All patients recovered with macrolide therapy, and no deaths occurred. Conclusions: Infantile C. trachomatis pneumonia typically presents with absent or low-to-moderate fever, paroxysmal cough, and occasional wheezing. Tachypnea and retractions may serve as early indicators of severe disease. Atypical chest imaging patterns, including mass-like and miliary opacities, provide valuable diagnostic clues. Once the diagnosis is established, prompt initiation of macrolide therapy is recommended, and the overall prognosis is favorable.