Therapeutic benefit of growth hormone in achrondroplastic dwarfism

Height Outcome of Recombinant Human Growth Hormone Treatment in Achondroplasia Children: A Meta-Analysis

BACKGROUND/AIMS

Although recombinant human growth hormone (rhGH) is not approved to treat short stature of achondroplasia (ACH), some studies suggested growth improvement during short-term rhGH treatment.

METHODS

A meta-analysis of rhGH therapy efficacy in ACH children was performed.

RESULTS

From 12 English-language studies, 558 (54.0% males) rhGH-treated ACH children were enrolled. Administration of rhGH (median dosage 0.21 mg/kg/ week; range 0.16-0.42 mg/kg/week) improved height (Ht) from baseline [-5.069 standard deviation score (SDS; 95% CI -5.109 to -5.029); p < 0.0001] to 12 [-4.325 SDS (95% CI -4.363 to -4.287); p < 0.0001] and 24 months [-4.073 SDS (95% CI -4.128 to -4.019); p < 0.0001]. Then, Ht remained approximately constant up to 5 years [-3.941 SDS (95% CI -4.671 to -3.212); p < 0.0001].

CONCLUSIONS

In ACH children, rhGH treatment increased Ht from -5.0 to -4.0 SDS during 5 years, but insufficient data are available on both the adult Ht and the changes of body proportions.

Achondroplasia

Achondroplasia is the most common form of short limb dwarfism in human beings, affecting more than 250,000 individuals worldwide. More than 95% of patients have the same point mutation in the gene for fibroblast growth factor receptor 3 (FGFR3) and more than 80% of these are new mutations. The mutation, which causes gain of FGFR3 function, affects many tissues, most strikingly the cartilaginous growth plate in the growing skeleton, leading to a variety of manifestations and complications. The biology of FGFR3 and the molecular and cellular consequences of the achondroplasia mutation are being elucidated, providing a more complete understanding of the disorder and a basis for future treatments targeted directly at relevant pathogenetic pathways. Furthermore, the natural history of the condition, which has been well delineated in childhood and adolescence, is being defined more fully in adults with achondroplasia; most of the serious complications can be modified favourably or prevented by anticipation and early treatment. Possible future treatments include chemical inhibition of receptor signalling, antibody blockade of receptor activation, and alteration of pathways that modulate the downstream propagation of FGFR3 signals.

Achondroplasia: recent advances in diagnosis and treatment

Achondroplasia (ACH) is the most common form of chondrodysplasia in humans. This disorder is inherited as an autosomal dominant trait, though most cases are sporadic. Recent advances in molecular biology have revealed its genetic defect in fibroblast growth factor-3 gene. This may introduce a new diagnostic tool and the classification of ACH and related disorders. Recent molecular engineering techniques have made it possible to provide large amounts of the various kinds of biofactors, such as erythropoietin, granulocyte colony stimulating factor and human growth hormone (GH), for clinical use. In fact, GH has been widely used to treat non-GH-deficient forms of short stature, such as Turner's syndrome, skeletal dysplasia, intrauterine growth retardation, chronic illness and idiopathic short stature, with beneficial effects. This may also be introduced into the medical management of ACH.

Response to growth hormone in children with chondrodysplasia

Theoretic concerns exist that children with chondrodysplasia will not grow in response to growth hormone (GH) therapy because of an inability of the abnormal growth cartilage to respond. Experience to date, however, suggests that there is an increase in growth velocity, especially during the first year of treatment, which may be beneficial. Growth has increased during the early phases of GH therapy in both patients with achondroplasia and patients with hypochondroplasia. Fourteen patients with achondroplasia in the National Cooperative Growth Study have been treated with an average dose of GH of 0.317 mg/kg per week for an average of 2.6 years and have gained an average of 0.7 SD in height. Twenty patients with hypochondroplasia in the National Cooperative Growth Study have been treated with an average dose of GH of 0.317 mg/kg per week for an average of 2.6 years and have gained an average of 0.7 SD in height. These data suggest that the abnormal growth cartilage in patients with chondrodysplasia responds to GH therapy. The effect on final height cannot be predicted with the currently available data.

Anthropometry in skeletal dysplasia

Skeletal dysplasia or osteochondrodysplasia is the designation of more than 200 different disorders, that are characterized by abnormalities of the skeleton, disproportional short stature, and a variety of other problems. The underlying biochemical defect is unknown in the vast majority of skeletal dysplasias, and the diagnosis is based on radiological findings and anthropometric measurements. Despite this fact, the information on body proportions in even the more common forms of skeletal dysplasia is scarce. Patients with achondroplasia are often diagnosed shortly after birth. Linear growth is severely compromised with relatively short extremities. Head circumference is above normal and final height ranges from 115 to 145 cm in males and 112 to 137 cm in females. Individuals with hypochondroplasia may go unnoticed until puberty, at which time the growth problem becomes obvious. Sitting height to height ratio is increased, but the body disproportion may not be apparent until puberty. Final height has been reported between 118 and 165 cm. Spondyloepiphyseal and spondylometaepiphyseal dysplasias are characterized by severe impairment of growth both in trunk and extremities, and therefore the sitting height to height ratio may be normal. Final height is severely reduced and ranges from 94 to 132 cm. It is concluded that anthropometric studies of patients with skeletal dysplasia are needed. More quantitative information on body proportions may assist in the diagnostic procedure and ensure that growth promoting therapy, e.g. growth hormone, does not worsen the disproportion.