Different Growth Responses to Recombinant Human Growth Hormone in Three Siblings with Isolated Growth Hormone Deficiency Type 1A due to a 6.7Kb Deletion in the GH1 Gene

Isolated growth hormone deficiency (IGHD) type 1A is a rare, autosomal recessive disorder caused by deletion of the GH1 gene and characterized by early onset severe short stature and typical phenotype. Lack of exposure to GH during fetal life often leads to formation of anti-GH antibody following exposure even the least immunogenic recombinant human GH (rhGH). Some patients with circulating anti-GH antibodies demonstrate lack of growth response to GH while others do not. However, the clinical significance of this antibody is unclear; hence testing is not routinely recommended. Three siblings, born of a consanguineous union, were referred with severe short stature. They were evaluated and IGHD was diagnosed in all of them. Genetic analysis revealed that all three had homozygous 6.7 Kb deletion in GH1 gene, while their parents displayed a pattern of heterozygous 6.7 Kb deletions. rhGH was started at 10, 6 and 1.58 years of age, respectively. Growth and hormonal parameters were monitored throughout the course of treatment. The eldest sibling demonstrated expected growth velocity (9.5 cm/year) for the first year of rhGH that rapidly waned thereafter (2.5 cm/year). The youngest sibling experienced excellent growth response even after the third year (10.3 cm/year) while the middle sibling displayed sub-optimal response from rhGH initiation (6.3 cm/year). Change of rhGH brand did not work in the two elder sisters. Such a different growth response with rhGH in three siblings harbouring similar genetic abnormality has not been described previously.