Altered body fat, metabolic disturbances common in SMA adults
Adults with spinal muscular atrophy (SMA) showed alterations in body composition and metabolic disturbances, including changes in blood sugar and fats, that could leave them vulnerable to cardiometabolic complications, a study shows.
People with SMA type 2 and those who weren’t ambulatory, meaning they couldn’t walk, showed the greatest alterations in body composition and blood sugar.
“Adult patients with SMA had abnormal body composition and highly prevalent metabolic disturbances that might increase cardiometabolic risk,” wrote the researchers, who noted, however that “because treatments have modified the course of SMA, it is important to investigate whether these observations translate into clinically relevant outcomes.”
The study, “The endocrine manifestations of adults with spinal muscular atrophy,” was published in Muscle & Nerve.
Changes in body composition, such as the makeup of fat, muscle, and other tissue, influences the function of the endocrine system, or hormone-producing tissues that regulate a range of bodily functions. This can cause metabolic changes such as altered blood sugar (glucose), fats, or sex hormones.
Preclinical studies show there are signs of impaired glucose metabolism and elevated fats (hyperlipidemia) in the bloodstream of animal models of SMA. Moreover, in pediatric SMA populations, studies show a high prevalence of metabolic disturbances, including elevated blood glucose, dysregulated fats, and altered sex hormones. These endocrine alterations haven’t been studied as much in adults with SMA, although some research indicates the presence of metabolic alterations in this population.
Effects on body composition
Here, researchers conducted a cross-sectional study on the endocrine manifestations of 29 adults with SMA types 2, 3, or 4, who were seen at a Slovenian clinic in 2022. All but two were receiving disease-modifying therapies and nearly three-quarters of them (75.9%) exhibited an increased proportion of body fat mass relative to a normal healthy range despite more than half (51.7%) having a normal overall weight.
Fat-free mass (FFM), which looks at mass accounted for by things other than fat (e.g. muscle, bone), was below the median normal range in 34.5% of the patients and below the 90th percentile in more than half (55.2%).
SMA type and ambulation status appeared to have an effect on body composition. Patients with SMA type 2 had significantly lower FFM, but a higher proportion of fat mass than the pooled group of patients with SMA types 3 or 4. Likewise, nonambulatory patients had a lower FFM and higher fat mass than ambulatory patients.
Metabolic changes were prevalent across the entire patient group, with 93.1% showing some type of disturbance.
Nearly a third of patients had diabetes (32.1%), while a similar proportion had impaired glucose tolerance (32.1%), where blood sugar is elevated, but not high enough to be considered diabetes. Relative to pediatric populations, impaired glucose tolerance was “twice as common,” among the adults studied, the scientists said.
Patients with SMA type 2 and nonambulatory patients generally showed signs of more disrupted glucose metabolism than those with SMA types 3 or 4, or those who were ambulatory.
Moreover, 44.8% showed signs of significant insulin resistance, where the body’s cells don’t respond normally to the hormone insulin that regulates blood sugar.
Elevated beta-hydroxybutyrate (BHB), a marker of ketosis, where the body doesn’t have enough sugar to burn for energy so it instead burns fat, was observed in 37.9%.
Lipid abnormalities were also common, with at least one abnormality type observed in 89.7% of patients, and more than two-thirds showing either two or three abnormalities. For example, 69% of patients had elevations in the blood of total cholesterol and more than a third (34.5%) had elevations in triglycerides. No differences were observed between SMA types or having the ability to walk.
Among male patients, more than half showed signs of some type of hypogonadism, when the testes produce little or no sex hormones, such as testosterone.
The findings “suggest that multiple endocrine abnormalities are prevalent in adults with SMA,” wrote the researchers, who added that “active screening and treatment of endocrine abnormalities in SMA patients should be considered” as these problems can ultimately lead to more serious cardiometabolic complications. They said nonambulatory patients seem to be at the highest risk..
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