What is HI?

What is Congenital Hyperinsulinism?

Congenital hyperinsulinism (CHI) is a rare condition in which the pancreas produces too much insulin. Insulin lowers blood sugar, so excess insulin can cause dangerously low blood glucose levels (hypoglycaemia).

When does Congenital Hyperinsulinism present?

The condition most often appears in newborn babies, but it can also develop later in infancy or childhood. The image below highlights some of the possible symptoms.

Types of hyperinsulinism

Transient hyperinsulinism

This type usually improves over time and is more common in:

• Babies born to mothers with diabetes

• Babies who experienced stress around birth (such as lack of oxygen)

• Babies who were small for their gestational age

In rare cases, transient hyperinsulinism may have a genetic cause.

Persistent hyperinsulinism

Persistent CHI does not resolve on its own and often requires long-term treatment. Many babies with persistent CHI are larger than expected at birth because of high insulin levels before birth. Most persistent cases are caused by changes in a single gene. CHI can also occur as part of a genetic condition such as Beckwith–Wiedemann syndrome.

Why early diagnosis is important?

Low blood sugar can damage the developing brain, so early diagnosis and treatment are essential. Doctors may suspect CHI if a baby needs unusually high amounts of glucose through a drip to keep blood sugar levels normal.

CHI is diagnosed using blood tests taken during episodes of low blood sugar. These tests show insulin levels that are higher than expected, along with low levels of fats and ketones, which are normally produced when blood sugar is low.

How common is congenital hyperinsulinism?

Between 2007 and 2016, we studied how often babies in the UK were diagnosed with congenital hyperinsulinism. We found 278 children with CHI that lasted longer than six months. From this, we estimated that CHI affects at least 1 in every 28,389 babies born in the UK (Yau, et al. PLoS One, PMID: 32027664).

This is similar to rates in other countries where parents are often not closely related. In countries where relatives (such as cousins) have children together more often, CHI can be more common because some forms are inherited in a recessive way, meaning a child must inherit the altered gene from both parents.