Background: Variation in karyotype may be associated with the phenotype of patients with Turner syndrome (TS). Our objective was to identify these associations between karyotype and phenotype in TS patients.

Methods: This study was part of the European multicentre dsd-LIFE study. We evaluated the associations between different karyotypes of TS patients and age at diagnosis, Turner stigmata, cardiac/renal involvement (bicuspid aortic valve, aortic coarctation and horseshoe kidney), spontaneous puberty, puberty induction, and FSH at diagnosis.

Results: Information was available for 328 TS patients (median 28 (15-73) years of age). Participants had a monosomy 45,X (46%), mosaicism 45,X/46,XX (10%), a karyotype with isochromosome (18%), or other karyotype (26%). The median age at diagnosis was slightly lower in the monosomy 45,X group (10 (0-61) versus 11 (0-39) years; p=0.025). Patients with a monosomy 45,X more often had typical Turner stigmata and cardiac malformations, and less spontaneous puberty compared to the other karyotypes, whereas women with mosaicism 45,X/46,XX showed the lowest prevalence rates of Turner stigmata or related conditions. Patients with isochromosome and y-material showed an intermediate phenotype.

Conclusion: These results show that the clinical signs of TS are the most severe in patients with monosomy 45,X and the least severe in patients with mosaicism 45,X/46,XX. Despite the more severe features in patients with monosomy 45,X, the median age at diagnosis was only slightly lower compared to patients with other karyotypes, which suggests opportunities for improvement of knowledge and diagnostics.