Adults with MPS Disorders Not More Susceptible to Diabetes, High Cholesterol, Study Suggests

Adults with mucopolysaccharidosis (MPS), including MPS III, also known as Sanfilippo syndrome, have normal blood cholesterol levels and do not show a higher incidence of diabetes, despite their higher body mass index and increased cardiovascular risk, a study has found.  

The report strongly suggests that high levels of lipids, or fat molecules, in circulation are not the reason why this group of patients is more susceptible to cardiovascular conditions.

The study, “The factors affecting lipid profile in adult patients with Mucopolysaccharidosis,” was published in the journal Molecular Genetics and Metabolism Reports.

MPS encompasses a group of rare genetic disorders marked by the excessive buildup of glycosaminoglycans (GAGs), a class of large sugar molecules, within cells.

GAGs can accumulate inside muscle cells and in blood vessels that supply blood to heart muscles, known as coronary arteries, leading to their narrowing and malfunction and resulting in coronary artery disease.

Other heart conditions can also affect MPS patients, such as malfunction of the heart’s valves.

It is still unknown why certain heart disorders are common among MPS patients and why GAG accumulation is linked to an increased cardiovascular risk.

Estimating these risks is very important for MPS patients, since heart conditions can increase the risk of death and complications, and pose additional threats to those undergoing surgery.

However, no validated biomarkers have been found that may help doctors predict the risk of cardiovascular or coronary artery disease in this patient population.

Researchers at The Mark Holland Metabolic Unit at Salford Royal Foundation NHS Trust in the U.K. hypothesized that a higher content of lipids in MPS patients’ blood could be linked to their increased risk of heart disease.

To confirm whether or not their hypothesis was true, they looked for alterations in the lipid profile of people with different types of MPSs and investigated if these changes would contribute to the risk of cardiovascular issues.

A total of 82 adults older than 16 with MPS type I (28 patients), type II (16 patients), type III (four patients), type IV (24 patients), and type VI (10 patients) were included in the study; 29 were females, and 53 were males. Patients were recruited from two U.K. clinics specializing in inherited metabolic disorders.

A lipid profile — a blood test measuring different types of fats in the serum including total cholesterol, HDL-cholesterol (the “good” cholesterol), LDL-cholesterol (the “bad” cholesterol), and triglycerides — was determined for all patients.

Individuals were also tested for blood lipoprotein-a (considered a risk factor for heart disease), and given a glucose tolerance test (GTT) or a glycated hemoglobin (A1C) test to screen for diabetes.

In all MPS types, there were patients who were overweight, with a higher than normal body mass index. However, blood sugar tests indicated that, except in one case, none of the patients had abnormal blood sugar results or diabetes. In three patients, insulin was also analyzed during GTT, but none had signs of insulin resistance (a precursor condition of diabetes), despite being overweight.

Mean values of total cholesterol, HDL-cholesterol, LDL-cholesterol  and triglycerides were within normal ranges for all five MPS types.

The presence or absence of treatment, including enzyme replacement therapy or hematopoietic stem cell therapy, did not significantly influence the lipid profile in MPS I and MPS IV patients, and affected it very little in MPS VI patients.

Lipoprotein-a results, available only for six MPS IV patients, also were not significantly different from normal values, suggesting this biochemical marker is not useful in predicting cardiovascular disease in this group of patients.

This study provided the largest lipid profile data set to date in adults with MPSs, indicating that “MPS disorders are not associated with significant hypercholesterolaemia [high blood cholesterol] or diabetes mellitus despite increased BMI [body mass index],” according to the researchers.

The results, however, are inconclusive as to why cardiovascular risk is increased in people with MPSs.

“Whether long-term cardiovascular risk is dependent on lipid profile, diabetes, obesity or GAGs deposition within the organ system remains unanswered,” the authors wrote. 

They conclude that more research is necessary to understand the causes of cardiovascular disorders in these patients, proposing “the measurement of carotid intimal thickness [ultrasound exam that measures the thickness of the inner two layers of the carotid artery] as a potential surrogate marker of coronary artery disease.”