Table 1.

Classification of isolated GH deficiency

IGHD type	Genetic abnormalities	Inheritance	GH levels	Growth response to GH	Pituitary imaging	Comments
IA	GH1 gene deletions and nonsense mutations	AR	Absent	Transitory	AP: normal or hypoplastic	Often have anti-GH antibodies after GH replacement
					PP: eutopic
IB	GH1 gene splice site mutations	AR	↓	Yes	AP: normal or hypoplastic
	GHRHR gene mutations				PP: eutopic
II	GH1 gene splice site and missense mutations and intronic deletions	AD	↓	Yes	AP: normal or hypoplastic	Variability in height
					PP: eutopic	May develop additional pituitary hormone deficiencies
III	BTK or unknown	X-linked	↓	Yes	PP: ectopic or normal	Agammaglobulinemia
						May have mental retardation

AR, autosomal recessive; AD, autosomal dominant; AP, anterior pituitary; PP, posterior pituitary; GHRHR, growth hormone-releasing hormone receptor; BTK, Bruton's tyrosine kinase; ↓, low but detectable.