Idiopathic short stature (ISS) is a condition where a child is significantly shorter than their peers without a detectable medical cause. It is a diagnosis of exclusion, applied only after a thorough medical evaluation fails to find an underlying disease, hormonal deficiency, or genetic syndrome. To be diagnosed, a child’s height is below the 2.3rd percentile for their age and sex. These children are otherwise healthy, with normal body proportions and no illness explaining their limited growth.
How Doctors Diagnose Idiopathic Short Stature
A pediatric endocrinologist tracks the child’s growth over time by plotting height and growth velocity on standardized charts. The family’s medical history, including the heights of parents and relatives, is also reviewed to calculate the child’s genetic height potential, known as the mid-parental height.
A key step is determining the child’s skeletal maturity, or “bone age,” using an X-ray of the left hand and wrist. This assessment compares bone development to chronological age and helps predict potential adult height. A significant delay in bone age might suggest a constitutional delay of growth and puberty, often called being a “late bloomer,” rather than ISS.
To rule out other causes, a series of blood tests screens for hormonal imbalances like growth hormone deficiency and hypothyroidism. Doctors also check for chronic conditions such as celiac disease or kidney problems that can impair growth. For girls, a karyotype analysis is often conducted to rule out Turner syndrome. If all these tests come back normal, the diagnosis of ISS is confirmed.
Suspected Causes and Genetic Links
While the term “idiopathic” means the cause is unknown, research points toward a strong genetic influence. The condition often runs in families, a subtype referred to as familial short stature (FSS), where a child’s height is consistent with the stature of their parents. This is distinct from a child who is significantly shorter than their family’s typical height.
Many cases of ISS are now thought to be polygenic, resulting from the combined effects of many common genetic variants, each with a small impact on height. Advancements in genetic sequencing have also identified monogenic causes, where a mutation in a single gene is responsible for the short stature. These single-gene variants can be inherited in an autosomal dominant pattern, where only one parent needs to carry the gene.
These genetic variations can subtly affect the growth hormone (GH) and insulin-like growth factor 1 (IGF-1) axis. Unlike in classical GH deficiency, children with ISS produce normal levels of growth hormone. The issue may lie in how their bodies respond to it, due to variations in the GH receptor or other signaling proteins. Other identified genes, such as SHOX, NPR2, and ACAN, are directly involved in the development of the growth plates in bones, and mutations in these genes can lead to a milder form of skeletal dysplasia that presents as ISS.
Growth Hormone Treatment for ISS
The primary medical intervention for children with ISS is treatment with recombinant human growth hormone (rhGH). This hormone was approved by the FDA in 2003 for children with ISS whose predicted adult height is significantly below the average range. Eligibility requires a predicted adult height of less than 5’4″ for males or 4’11” for females. The treatment involves daily subcutaneous injections at home, usually in the evening to mimic the body’s natural release of growth hormone.
The goal of rhGH therapy is to increase a child’s growth velocity and final adult height. Studies show treatment can increase final height by an average of two to four inches, though individual results vary. Treatment is most effective when started early and continues for several years until the growth plates fuse after puberty.
The decision to start rhGH treatment involves careful consideration of several factors. The daily injections can be a burden, the treatment duration can last for many years, and the cost is substantial. While considered safe, potential side effects can include headaches, joint pain, and an increase in pressure within the skull.
Supporting a Child’s Well-Being
Beyond medical treatment, supporting a child’s emotional and psychological health is a fundamental aspect of managing ISS. Children with short stature may face social challenges, like teasing or being treated as younger than they are, which can impact their self-esteem. Parents can foster resilience by creating a supportive home environment that values the child for their character and abilities rather than their physical size.
Open communication is important, and parents can help their child develop effective coping strategies for handling negative comments from peers. This might involve practicing simple, confident responses or using humor. Focusing on the child’s strengths, whether in academics, sports, or arts, helps build confidence that is not tied to their height. Emphasizing what their body can do, rather than how it looks, promotes a positive body image.
Some children may experience more significant behavioral or emotional difficulties, such as anxiety or social withdrawal. If a child is struggling to cope, or if parents feel overwhelmed, seeking support from a mental health professional can be beneficial. A therapist can provide tools for the child and family to navigate social pressures and build a strong sense of self-worth.