Estrogens are responsible for the disappearance of growth cartilage in the long bones at the end of the pubertal growth spurt both in boys and in girls. It is therefore hypothesized that stopping pubertal development and hence estrogen production, will prolong and increase the pubertal growth spurt, especially when growth hormone is given concommitantly.

Boys in early puberty, with a bone age between 11 and 13 years and a predicted adult height below 163 cm or girls in early puberty with a bone age between 10 and 12 years and a predicted height under 151 cm will be treated with triptorelin 3.75 mg and Zomacton growth hormone for 4 years.

Inclusion Criteria:

• Adult height prediction below -2.5 SD : 151 cm for girls and 164 cm for boys based on the vlaamse groeicurve 2004 (vub.ac.be/groeicurven)
• Pubertal: breast development at least M2 for girls and at least 4 ml of testicular volume for boys
• Bone age >10 years but < 12 years for girls and > 11 but < 13 years for boys
• Signed informed consent

Exclusion Criteria:

• Adopted children ( different genetic background, lack of data on birth parameters and parents)
• Bone dysplasia or sitting height/ total height > 2 SDS on standards by Gerver et al (see appendix)
• Chronic use of glucocorticoids
• Previous growth promoting therapy such as GH, sex steroids, oxandrolone,
• Known GH deficiency
• Chronic infectious disease
• Active rheumatic disease
• Previously diagnosed or currently suspected malignancy
• Sex steroid therapy
• Diabetes mellitus
• Renal insufficiency (serum creatinine > 1.5 mg/dl)
• Hepatic disease ( liver test > 4 fold upper limit of normality)
• Current congestive heart failure
• Inability to follow the study protocol
• Treatment with a non registered drug during the last 30 days before the moment of inclusion.