Common Causes & Symptoms of Rabson-Mendenhall Syndrome

Rabson-Mendenhall Syndrome

Rabson-Mendenhall Syndrome (RMS) is a rare genetic disorder caused by inherited mutation in the INSR gene, which provides instructions for making insulin receptors. This genetic disease is characterised by severe insulin resistance. It is one of a group of inherited disorders known as genetic syndromes of severe insulin resistance.  
Normally, after eating, food is broken down into glucose, which enters the bloodstream. The pancreas releases insulin, which acts like a key. It binds to receptors on cells, signalling them to absorb glucose from the blood to be used for energy. Imagine your body not being able to do that. Insulin is a key hormone that signals cells to absorb glucose (sugar) from the bloodstream. In RMS, mutations in the insulin receptor mean cells cannot receive this signal properly. Consequently, glucose cannot enter cells efficiently to be used for energy, leading to its buildup in the blood.

In Rabson–Mendenhall syndrome, severe insulin resistance leads to early-onset insulin-resistant diabetes and persistent hyperglycemia, often beginning in infancy or early childhood.

They suffer from insulin resistance, which results in dangerously high blood sugar and other physical complications. Keep reading to learn about the causes of RMS, whether genetics matter, and its diagnosis and treatment.

What Causes Rabson-Mendenhall Syndrome (RMS)?

A mutation in the INSR (insulin receptor) gene is the underlying cause of Rabson-Mendenhall syndrome. This gene contains information on creating a protein called insulin receptors, and the mutation disrupts their function. Insulin receptors are present on the surface of cells, and insulin binds to them. Insulin receptors are embedded in the outer membrane surrounding the cell, in which they bind to insulin circulating in the bloodstream. The issue in RMS lies with the receptors, not the insulin.

The mutation causes the insulin receptors to malfunction. Although insulin present in the bloodstream, without enough functional receptors it is less able to exert its effects on cells and tissues. This severe resistance to the effects of insulin damages the regulation of blood glucose and influence many aspects of development in people with Rabson-Mendenhall syndrome.

They either don't function properly or are entirely unresponsive to insulin. Thus, causing severe insulin resistance and high blood sugar in RMS patients.

What are the Symptoms of Rabson-Mendenhall Syndrome (RMS)?

Symptoms of RMS start appearing in the first year of life. In some cases, complications can be more severe than others. But the general symptoms and signs include:

• Dry, thick, and acanthotic skin, deep grooves in the tongue, large ears, nose, and lips.
• Acanthosis nigricans, the darkening and thickening of skin. A velvety feeling on the skin of the underarms and neck (under the folds of the skin).
• Abnormal growth of teeth and nails.
• Excess hair growth (hirsutism)
• Swelling in and around the belly
• Weak muscles
• Severe fasting hyperglycaemia (high blood sugar)
• Postprandial hyperglycaemia (high blood sugar after eating)
• Polyuria (excessive urination)
• Polydipsia (excessive thirst)
• Failure to thrive and severe growth retardation despite hunger (polyphagia)
• Recurrent infections due to hyperglycaemia impairing immune function
• Diabetic ketoacidosis (DKA), a life-threatening condition

Is Rabson-Mendenhall Syndrome (RMS) Inherited?

Rabson-Mendenhall Syndrome is autosomal recessive. The patient must inherit two mutated INSR genes from both parents. So, here’s what can happen:

• Receiving a mutated gene from both mother and father: Affected
• Receiving one mutated and one normal gene from either parent: Carrier
• Receiving two normal genes: Unaffected

Although RMS cannot be prevented once inherited, genetic counseling and carrier testing can help at-risk families understand and reduce recurrence risk.

How is Rabson-Mendenhall Syndrome (RMS) Diagnosed?

Extremely high blood sugar levels are typical in people with RMS, and we know that it is autosomal recessive. Diagnosis typically occurs in childhood, often between ages 1-12, when characteristic signs like severe insulin-resistant diabetes and acanthosis nigricans become apparent. The diagnostic process involves:

• Testing for blood sugar irregularities,
• Observation of symptoms,
• Genetic testing to detect a mutation in the INSR gene.

What are the Treatments for Rabson-Mendenhall Syndrome (RMS)?

There is no cure for this condition. Since it comes with complications and physical symptoms, treatment for a better life is the only way.

The essential step in this treatment involves maintaining a stable blood glucose level. Treatments for high blood sugar (hyperglycaemia) that have worked so far are:

• Leptin: It is a hormone produced by fat cells in the body to regulate appetite and metabolism. Leptin therapy has been explored experimentally in a small number of patients with severe insulin resistance, including RMS, with variable and limited benefit.
• Biguanides: Medicines given to patients to reduce the formation of glucose in the body.
• rhIGF-I (recombinant human insulin-like growth factor I): Recombinant human IGF‑I may partially bypass insulin receptor dysfunction and improve glucose uptake, but its use is limited, closely monitored, and associated with significant adverse effects.

The rarity of a disease like Rabson-Mendenhall Syndrome (RMS) makes its awareness and early diagnosis important. While there is no cure, symptom management and counselling play a key role in improving the lives of the affected. Ongoing research on rare diseases and gene therapy also offers hope for the future.

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