Children with achondroplasia experienced an adolescent growth spurt, which was similar in shape and half the magnitude of the non-achondroplasia population.

There is a lack of knowledge about longitudinal growth during childhood in achondroplasia. We report patterns of linear growth and height growth velocity references. The sample consisted of 84 children, 41 girls and 43 boys. Growth data was collected from birth until mid-childhood. The median (interquartile range) number of measurements per child was 13.5 (12, 15). Individual growth curves were estimated by fitting the Reed 1st model to each individual's height for age data. Height growth velocities references for age centiles were calculated by LMS method.Mean (SD) birth length was 46.14 cm (2.17) and 45.53 cm (2.16), for boys and girls respectively.Individual growth curves were analyzed. Shifts in growth channels were seen: out of 84 infants, 41 (48.8%) changed more than 1 SDS between birth to 5 years old. The numbers of infants shifting upward were similar (20/84) to the infants shifting downward (21/84). Height growth velocity curves show that after a period of fast decreasing growth velocity since birth, with a mean of 15.5 cm/year and 9.5 cm/year at 6 month and 1 year old, the growth velocity is stable in late preschool years, with a mean of 4.3 cm/year. Shifts in growth channels were seen between birth and 5 years old. Professionals who follow up them must consider this phenomenon during infancy. ACH children experienced a period of fast decreasing growth during infancy and the growth curve was similar in shape and lesser in magnitude than the general population.

Growth is a discontinuous and irregular process, present not only in long bones but also in skull bones. Although long-term growth curves of head circumference and supine length are different, when measured on a daily basis findings suggest that skull and long bones have a common pattern; the physiological basis needs future research.

Our findings support the concept of growth as a non-linear and irregular process with three phenomena: Stasis, steep changes and continuous growth present in all ages, including infancy, school age and adolescence.

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