Isolated growth hormone deficiency type IB

Isolated growth hormone deficiency type IB (IGHD IB) is a rare genetic disorder characterized by a severe deficiency of growth hormone (GH) produced by the anterior pituitary gland, leading to significant postnatal growth failure. Unlike type IA, patients with type IB have low but detectable levels of growth hormone. The condition is caused by homozygous or compound heterozygous mutations in the GH1 gene (growth hormone 1) on chromosome 17q23.3, or less commonly in the GHRHR gene (growth hormone releasing hormone receptor) on chromosome 7p14. These mutations result in reduced but not completely absent GH production. Clinically, affected children present with proportionate short stature, typically becoming apparent in infancy or early childhood. Key features include growth deceleration, delayed bone age, a prominent forehead, midfacial hypoplasia (underdevelopment of the midface), and increased truncal adiposity. Hypoglycemia may occur in infancy. Unlike IGHD type IA, patients with type IB do not develop anti-GH antibodies when treated with exogenous growth hormone, because they have some endogenous GH production and are therefore immunologically tolerant to the hormone. Treatment consists of recombinant human growth hormone (rhGH) replacement therapy, which is generally well tolerated and effective in improving linear growth. Patients with type IB typically respond favorably to GH therapy without the formation of blocking antibodies, which distinguishes their treatment course from that of type IA patients. Early diagnosis and initiation of therapy are important to optimize final adult height. Long-term monitoring of growth velocity, IGF-1 levels, and other pituitary functions is recommended throughout treatment.

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