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 (GH) deficiency type I A 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 to the least immunogenic recombinant human GH (rhGH). Some patients with circulating ant-GH antibodies demonstrate lack of growth response to GH while others do not. However, the clinical significance of this antibody is unclear hence not routinely recommended. Three siblings born of a consanguineous union were referred to us with severe short stature. They were evaluated and IGHD was diagnosed in all of them. Genetic analysis revealed homozygous 6.7 Kb deletions of GH1 gene in all of them while their parents displayed a pattern of heterozygous 6.7 Kb deletions. rhGH was started at 10, 6 and 17/12 years of age. Their growth and hormonal parameters were monitored throughout the course of treatment. The eldest sibling demonstrated usual growth velocity (9.5 cm/year) after start of therapy that rapidly waned after 1st year (2.5 cm/year). The youngest sibling experienced excellent growth response even after 3rd year (10.3 cm/year) while the middle one displayed sub-optimal response from beginning (6.3cm/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 earlier. Keywords: Isolated growth hormone deficiency type IA, GH1 gene, Anti-GH antibody.