Disease

There are a number of diseases and conditions that can affect growth. Some of the most common include conditions affecting the: 

• Heart and blood vessels (e.g. a congenital heart defect).
• Respiratory tract (e.g. asthma, cystic fibrosis).
• Stomach, liver, and intestines (e.g. celiac disease, Crohn's disease).
• Kidneys: e.g. chronic renal insufficiency (a type of long term kidney disease).
• Pituitary gland. 

Please note that not all children with the above conditions are smaller than their peers. Growth failure is only one possible consequence and often occurs if the condition is severe or not treated properly. 

The pituitary gland plays a really important role in growth.

Conditions that affect the pituitary gland include: 

• Congenital (inborn) hypopituitarism (CHP): when the baby is born with a pituitary gland that doesn't seem to function properly. Children with CHP may have an abnormally small penis (micropenis) and undescended testicles in boys, cleft lip and/or palate, significantly reduced blood sugar (hypoglycemia), jaundice and shock symptoms (such as very low blood pressure) and problems regulating body temperature. The treatment of CHP includes growth hormone and aims to replace the missing hormones. Boys will also be given testosterone and girls oestrogen.
• Congenital GnRH deficiency (hypogonadotropic hypogonadism): in this condition there is a deficiency of the gonadotropin releasing hormone (GnRH). This hormone is produced by the hypothalamus and is involved in the physical changes that occur during puberty. Children with this condition may have a delayed puberty. Although at birth boys may have a small and thin penis (micropenis) and the testicles may have descended, the diagnosis usually occurs around the onset of puberty. Treatment usually includes sex hormones.
• Precocious puberty: children with this condition may have early puberty, from about  8 in girls and age 9 in boys​​. Symptoms include breast development in girls and testicle growth in boys. The causes are unclear, but may include problems with the hypothalamus and pituitary gland. Apart from psychological and social issues of precocious puberty, growth may stop earlier than usual due to the elevated levels of sex hormones. Precocious puberty can be treated with sex hormones.  
• Growth hormone deficiency (GHD): GHD can occur as a result of a disease in the hypothalamus or pituitary gland. However, in some cases the cause may be unknown (this is known as idiopathic GHD). Children with GHD often have more fat around the trunk ("baby fat") and may have a finely shaped young looking face with very little or thin hair on their head. Children with GHD are treated with growth hormone.