Morquio A Syndrome May Be Most Common MPS in Mexico, Study Finds

Mucopolysaccharidosis (MPS) type IVA (Morquio A syndrome) is the most common type of MPS in Mexico, followed by MPS type III (Sanfilippo syndrome), according to five-year data of enzymatic activity tests at a reference center.

These findings are in contrast with what is reported for most countries, where Sanfilippo is the most common MPS and Morquio A syndrome is, at most, the second-most common.

Data also suggested that the country’s estimated frequency of MPS was 2.23 per 100,000 births, which is likely to be an underestimate compared with results acquired through newborn screening, the researchers noted.

The study, “Biochemical diagnosis of mucopolysaccharidosis in a Mexican reference center,” was published in the journal Genetic and Molecular Biology.

MPS refers to a group of inherited lysosomal storage disorders caused by deficiencies in specific enzymes responsible for breaking down glycosaminoglycans (GAGs) — long complex sugar molecules. Such deficiencies result in the accumulation of toxic deposits in various cells and tissues, leading to progressive damage.

MPS can be categorized into seven clinically distinct forms (and numerous subtypes) that vary in terms of age of onset, symptoms, and severity. Besides genetic tests, accurate MPS diagnosis is based on enzymatic activity tests that measure the activity of the disease-associated enzyme in a variety of cells or in the blood.

Researchers looked into MPS frequencies in Mexico using data from enzymatic activity tests ran at a reference center over a period of five years (from 2012–17).

The analysis included seven types of MPS — MPS I, MPS II (Hunter syndrome), MPS IIIA (Sanfilippo type A), MPS IIIB (Sanfilippo type B), MPS IVA (Morquio A syndrome), MPS VI (Maroteaux-Lamy syndrome), and MPS VII (Sly syndrome).

A total of 761 samples from 505 individuals with suspected MPS were analyzed. Samples came from all Mexico states except for Campeche. Most (86.6%) analyses concerned patients, while 10% were for patients’ siblings, and 3.4% for their parents. The mean age of the 443 (58.2%) patients with available data was 7.7 years old (range 0–48 years).

More than half of the samples (53.7%) were asked to be tested for only one enzyme, while nearly 30% were tested for two different enzymes. The most frequently requested tests were for Morquio A syndrome (31.4%) and Maroteaux-Lamy syndrome (23.3%), and the least frequent was for Hunter syndrome (5.7%).

MPS was confirmed in 198 (26.0%) samples, with nearly half of them (49.1%) being positive for Morquio A syndrome, followed by Sanfilippo syndrome, which accounted for 17.7% of positive cases (11.8% for type A, and 5.9% for type B). Sly syndrome accounted for 10.4% of positive cases, while the lowest frequencies of positive results were for MPS I (8.6%), Maroteaux-Lamy syndrome (7.5%), and Hunter syndrome (6.8%).

“These results differ from results that have been reported in other countries, in which MPS IVA is, at most, the second-most frequently diagnosed MPS,” the researchers wrote.

The team noted, however, that a previous Mexican study also showed Morquio A syndrome to be the most frequently diagnosed MPS, suggesting that this may well reflect the country’s reality.

The MPS types with the highest rate of confirmed diagnosis among the total samples tested for that disease were the combined Sanfilippo subtypes (44.3% overall; 29.9% for type A, and 14.5% for type B) and Morquio A (42.7%).

Morquio A’s high frequency of confirmed diagnosis may indicate that “this MPS is easier to diagnose for Mexican clinicians, which is probably due to its characteristic [features] or because this type is better known than other types,” the researchers wrote.

Further analyses estimated that Morquio A had a frequency of 1.10 per 100,000 births, Sanfilippo type A had a frequency of 0.26, and Sly syndrome of 0.23 per 100,000 births.

Also, the combined estimated frequency of MPS was 2.23 per 100,000 births, which was similar to that reported for Tunisia and reflected an intermediate position when compared with other countries.

Researchers highlighted that this MPS frequency may be underestimated, since not all MPS types were assessed in this study and it was not based on newborn screening — a more accurate method, but not routinely performed in Mexico.