Growth Problems in Sanfilippo Children Milder Than Those Seen in Other MPS Disorders, Study Suggests

Growth impairment among mucopolysaccharidosis (MPS) disorders is milder in people with MPS III (Sanfilippo syndrome) and most profound in those with MPS IVA (Morquio A syndrome), a study in Taiwanese patients suggests.

Its findings help in better understanding the characteristic growth patterns of each MPS type, which may aid in earlier diagnosis and in treatment.

The study, “Relationships among Height, Weight, Body Mass Index, and Age in Taiwanese Children with Different Types of Mucopolysaccharidoses,” was published in the journal Diagnostics.

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

MPS can be categorized into seven clinically distinct forms (and numerous subtypes) that vary in terms of age of onset, symptoms, and severity.

But short stature and growth impairment are a common feature of people with MPS disorders.

“Growth measurement is critical in the evaluation of therapeutic efficacy and disease progression in MPS,” the researchers wrote.

While several studies have described growth patterns in specific types of MPS, none has compared the growth features of different types of MPS within a single population.

Researchers in Taiwan looked at growth patterns in 129 young patients (89 male and 40 female) with different types of MPS. They were recruited at eight medical centers in Taiwan between January 1996 and December 2018.

Nine were diagnosed with MPS I (one with Hurler syndrome, six with Hurler–Scheie syndrome, and two with Scheie syndrome), 49 with MPS II (Hunter syndrome; 27 had the severe form and 22 the mild/intermediate form), 27 with MPS III (Sanfilippo syndrome), 30 with MPS IVA (Morquio A syndrome), and 14 with MPS VI (Maroteaux-Lamy syndrome).

Their mean age was 9.1 years (range of 8.4 months to 19.5 years) and none had received treatment before entering the study.

Researchers analyzed patients’ earliest recorded data on height, weight, body mass index (BMI), as well as birth weight and age at diagnosis.

Patients’ median age at diagnosis was 3.9 years among the 115 who had that data. Those with Hurler syndrome had the youngest median age at diagnosis (8.4 months), followed by Hurler-Scheie syndrome (2.2 years), MPS II severe form (3 years), MPS VI (3.2 years), MPS II mild/intermediate form and MPS IVA (4.2 years), MPS III (4.5 years), and Scheie syndrome (13.6 years).

Results showed that people with MPS IVA had the most significant growth impairment (in both height and weight), followed by those with MPS VI, MPS I, MPS II, and Sanfilippo syndrome, which showed the mildest impairment.

A slowing in growth was evident in MPS IVA patients earlier in childhood than in those with other MPS types.

Differences in height and weight between MPS patients and the general population were significantly more pronounced with increasing age, emphasizing the progressive nature of this disease.

A considerable number of MPS patients between ages 2–5 were taller and heavier than unaffected children, but their growth rates significantly dropped as they continued to age.

BMI values in these MPS patients were not significantly different from those of the general population.

“Understanding the growth curve and potential involved in each type of MPS may allow for early diagnosis and timely management of the disease, as well as accurate assessments of the therapeutic efficacy, which may improve the [patients’] quality of life,” the researchers wrote.

While these findings are consistent with previously reported data, the researchers noted that future and larger studies, with a longer follow-up period, are required to confirm their results and accurately determine growth patterns for each type of MPS.