Reference Growth Charts for Children With 47,XXY/Klinefelter Syndrome

BACKGROUND AND OBJECTIVES: Although tall stature is commonly associated with 47,XXY/Klinefelter syndrome (KS), detailed childhood growth patterns are not well-defined. This study aimed to develop KS-specific growth charts for stature-for-age, weight-for-age, weight-for-length (0-24 months), and body mass index (BMI)-for-age (2-18 years).

METHODS: We conducted a population-based secondary analysis using clinical data from 6 US pediatric centers. The cohort included 1279 males aged younger than 20 years with a diagnosis of KS and at least 1 outpatient measurement of height and/or weight. Nonparametric quantile regression was used to model age-related growth trajectories.

RESULTS: A median of 6 longitudinal growth data points per individual contributed to the creation of KS-specific curves. Key differences from standard reference growth charts included the following: (1) approximately 20% of boys with KS aged younger than 4 years were below the 5th percentile for height, whereas approximately 25% exceeded the 95th percentile by late childhood; (2) height velocity increased in midchildhood (after age 6 years), but without a distinct pubertal growth spurt; and (3) BMI distribution was broader, with approximately 10% of individuals below the 5th percentile and approximately 25% above the 95th percentile.

CONCLUSIONS: Boys with KS demonstrate distinct and variable growth trajectories compared with the general population. These KS-specific growth charts offer a valuable clinical tool for monitoring growth, guiding anticipatory counseling, and identifying atypical development patterns.