Growth hormone (GH) is a protein produced and secreted by the pituitary gland, a small organ situated at the base of the brain. It is a major regulator of growth, body composition, and metabolism, with its influence particularly pronounced during childhood and adolescence. During these developmental years, GH plays a significant role in promoting the growth and lengthening of long bones. A deficiency during this period prevents the biological processes necessary for normal physical maturation. This failure results in specific health issues that extend beyond simple limitations in height.
The Mechanism of Growth Hormone in Skeletal Development
GH does not act directly on bones for linear growth; instead, it operates through Insulin-like Growth Factor 1 (IGF-1). After GH is released, it travels to the liver, stimulating IGF-1 production and secretion into the bloodstream. Systemic IGF-1 then travels to the epiphyseal plates, or growth plates, located at the ends of long bones. These plates are composed of specialized cartilage cells called chondrocytes, responsible for all postnatal bone lengthening.
The process that lengthens the bone is called endochondral ossification, involving the continuous proliferation and differentiation of chondrocytes. IGF-1 is the principal factor driving the expansion of chondrocytes. It promotes the rapid division of these cells, causing the cartilage column to push outward. Without adequate GH and resulting IGF-1, proliferation and maturation slow dramatically, impeding new bone matrix formation and preventing normal elongation.
The Primary Consequence: Severe Growth Failure
The most direct consequence of GH deficiency during bone formation is a severe reduction in linear growth. Since the deficiency occurs before the growth plates naturally fuse at the end of puberty, the result is a failure to achieve a normal adult height. This condition is characterized by height falling substantially below the third percentile for age and sex, accompanied by a significantly slower growth velocity.
The short stature resulting from GH deficiency is typically proportionate, meaning the size of the limbs and trunk remain balanced. This distinguishes it from other skeletal growth disorders that cause disproportionate body dimensions. Skeletal development is also significantly delayed, evidenced by a bone age assessment (usually an X-ray of the left wrist and hand). This assessment reveals skeletal maturity often years behind the child’s chronological age. This delay can be beneficial, as it extends the window for potential therapeutic intervention before the growth plates fuse.
Secondary Developmental and Metabolic Effects
GH deficiency disrupts several systemic processes affecting maturation and body composition. GH regulates the body’s fat and muscle balance, and its absence leads to an altered distribution of mass. Children often exhibit increased visceral or truncal adiposity (fat accumulation around the abdomen) and a reduction in lean muscle mass.
The hormone also influences the timing of sexual maturation, frequently causing a delay in the onset of puberty. Furthermore, the development of teeth can be impaired, and children may appear younger than their actual age due to subtle craniofacial differences. GH also contributes to the acquisition of bone mineral density. Untreated GH deficiency can result in decreased bone mineralization, potentially leading to weaker bones and an increased risk for osteoporosis later in life.
Diagnosis and Treatment Strategies
Diagnosis involves a comprehensive evaluation based on clinical findings, growth patterns, and laboratory tests. The initial assessment relies on auxological data, including tracking the child’s height and growth velocity over time against established growth curves. A bone age X-ray is routinely performed to assess skeletal delay.
Biochemical confirmation is sought through measuring IGF-1 and its binding protein, IGFBP-3, as these levels reflect the body’s response to GH. Since GH is released in short, irregular pulses, a single random blood test is unreliable. Provocative GH stimulation tests are used, where the child is given a drug to stimulate GH release, and blood samples are taken over a few hours to measure the peak GH level.
The primary treatment for childhood GH deficiency is Growth Hormone Replacement Therapy (GH-RT), administered as a daily subcutaneous injection of recombinant human growth hormone. The goal is to maximize the final adult height and normalize the child’s growth trajectory. Treatment continues until the patient reaches an acceptable final height or until the growth plates fuse, preventing further skeletal lengthening.