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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Short-term growth during the pubertal growth spurt in these healthy girls is an irregular and discontinuous process, composed of three types of events: stasis, steep changes and continuous growth periods with a wide individual range of daily height increments.

ObjectivesIn general population, there are three phases in the human growth curve: infancy, childhood and puberty, with different main factors involved in their regulation and mathematical models to fit them. Achondroplasia children experience a fast decreasing growth during infancy and an “adolescent growth spurt”; however, there are no longitudinal studies that cover the analysis of the whole post-natal growth. Here we analyse the whole growth curve from infancy to adulthood applying the JPA-2 mathematical model.MethodsTwenty-seven patients, 17 girls and 10 boys with achondroplasia, who reached adult size, were included. Height growth data was collected from birth until adulthood. Individual growth curves were estimated by fitting the JPA-2 model to each individual’s height for age data.ResultsHeight growth velocity curves show that after a period of fast decreasing growth velocity since birth, with a mean of 9.7 cm/year at 1 year old, the growth velocity is stable in late preschool years, with a mean of 4.2 cm/year. In boys, age and peak height velocity in puberty were 13.75 years and 5.08 cm/year and reach a mean adult height of 130.52 cm. In girls, the age and peak height velocity in puberty were 11.1 years and 4.32 cm/year and reach a mean adult height of 119.2 cm.ConclusionsThe study of individual growth curves in achondroplasia children by the JPA-2 model shows the three periods, infancy, childhood and puberty, with a similar shape but lesser in magnitude than general population.

Background: Children with achondroplasia (ACH) appear to lack a pubertal growth spurt in height. Aim To explore the growth spurt in height and its segments sitting height and leg length, in a large sample of ACH cases using growth curve modelling. Subjects and methods: Height and sitting height were measured longitudinally in ACH children, and the data were analysed using the SITAR (SuperImposition by Translation and Rotation) growth model, which estimates a mean growth curve and random effects for individuals defining differences in size, pubertal timing and intensity. Results: Out of 402 ACH children, 85 boys and 75 girls aged 7-20 years had respectively 529 and 454 measurements of height and sitting height, with leg length calculated by difference. SITAR analysis identified peaks in mean height velocity at 13.3 and 11.3 years in boys and girls, with peak velocities of 4.3 and 4.4 cm/year. Mean peak velocity for sitting height was 3.0 cm/year, but leg length showed no peak. The SITAR models explained 92% to 99% of the cross-sectional variance. Conclusion: ACH children do experience a growth spurt in puberty, but only half that of control children. The spurt is due entirely to sitting height, with no leg length spurt.