Biochemical diagnosis of mucopolysaccharidoses over 11 years: the Egyptian experience

Biochemical diagnosis of Sanfilippo disorder types A and B

BACKGROUND

One of the 11 recognized mucopolysaccharidosis (MPS) diseases is Sanfilippo. It is autosomal recessive in its mode of transmission. There are four subtypes of Sanfilippo (A, B, C, and D). The most worldwide prevalent subtypes of mucopolysaccharidosis type III (MPS III) are A and B followed by C and D subtypes. To estimate the frequency of MPS IIIA among MPS III patients, we diagnose and compare their clinical features with those of MPS IIIB and also compare the prevalence of MPS IIIB versus MPS IIIA among diagnosed cases at the Biochemical Genetic Department at NRC. For every case that was referred, the quantitative determination of urine Glycosaminoglycans (GAGs) was assessed. Two-dimensional electrophoresis (2DE) of GAGs extracted from urine was performed on all cases with high urinary GAG levels. Both N-sulphoglucosamine sulphohydrolase (MPS IIIA) and N-alpha-acetylglucosaminidase (MPS IIIB) enzyme activity were determined fluorometrically.

RESULTS

From November 2019 to May 2022, 535 cases were referred to the National Research Centre's Biochemical Genetics Department. 233 (43%) MPS cases were diagnosed with high urinary GAG levels for their ages. 73 (31.3%) MPS III cases were diagnosed by 2DE out of the 233 MPS cases. Plasma N-alpha-acetylglucosaminidase enzyme assay was insufficient in 36 (49.3%) patients (Sanfilippo type B), while N-sulphoglucosamine sulphohydrolase enzyme activity was deficient in 15 (20.6%) patients. The other 22 (30.1%) patients are either Sanfilippo type C or D.

CONCLUSION

N-sulphoglucosamine sulphohydrolase enzyme activity was measured for the first time in Egypt. Thirty-one percent of all diagnosed MPS cases during the last 3 years were MPS type III, making Sanfilippo the most common MPS type among the referred cases to our Biochemical Genetics Department. MPS IIIA accounts for 20.6% of MPSIII cases in this study. Still, MPS type IIIB is the commonest type among diagnosed patients.

Mass spectrometry and two-dimensional electrophoresis in prenatal diagnosis of mucopolysaccharidosis type VI

Background

Mucopolysaccharidosis VI (MPS VI) or Maroteaux–Lamy syndrome is an autosomal recessive lysosomal storage disorder. Clinical manifestations are related to progressive accumulation of dermatan sulfate (DS). Two-dimensional electrophoresis has traditionally been used for the diagnosis of MPS disorders. The method is only qualitative and is time consuming. For prenatal diagnosis of MPS, 6–8 ml of amniotic fluid is required and 5 working days to complete. It needs personal experience to do the test and to interpret the results. Mass spectrometry (MS) is now available as a quantitative method and for prenatal diagnosis of MPS it needs less amniotic fluid and takes only 2 working days. It is more accurate, less person dependent, but it costs more. Our aim was to introduce quantitative determination of dermatan sulfate using mass spectrometry in the prenatal diagnosis of MPS VI in Egypt and to compare this technique to the classical qualitative diagnosis using two-dimensional electrophoresis (2-DEP) of the glycosaminoglycans (GAGs) in amniotic fluid. Thirty pregnant females each with single fetus were subjected to amniocentesis at 16 weeks gestation. Ten with a previously affected MPS VI infant and twenty served as controls. Prenatal diagnosis (PD) was done by both MS and 2-DEP.

Results

MS verified 2-DEP results which showed 5 affected and 5 non-affected fetuses with MPS VI.

Conclusion

Two-dimensional electrophoresis of the GAGs in amniotic fluid is a good qualitative method and MS was an accurate quantitative method for prenatal diagnosis of MPS type VI. Quantitative determination of GAGs in AF by mass spectrometry is quicker. Where prenatal diagnosis is recommended for at risk pregnancies, mass spectrometry could be used more in the future as it gives rapid and accurate results.

Prenatal diagnosis of mucopolysaccharidoses type II by two-dimensional electrophoresis and mass spectrometry in amniotic fluid

AIM

To introduce a quantitative determination of heparan sulfate and dermatan sulfate by mass spectrometry and to compare it with two-dimensional electrophoresis of the glycosaminoglycans in the amniotic fluid for the prenatal diagnosis of mucopolysaccharidoses type II (MPS II).

METHODS

Thirty pregnancies each with single fetus were subjected to amniocentesis at 16 weeks: 10 with a previously affected MPS II infant and 20 as controls. Prenatal diagnosis was done by both mass spectrometry two two-dimensional electrophoresis.

RESULTS

Two-dimensional electrophoresis showed four affected with MPS II and six unaffected fetuses. Mass spectrometry verified these results.

CONCLUSION

Two-dimensional electrophoresis of the glycosaminoglycans in amniotic fluid is a good qualitative method and mass spectrometry is a new accurate quantitative method for prenatal diagnosis of MPS II. Quantitative determination of glycosaminoglycans in amniotic fluid by mass spectrometry is both rapid and accurate. Prenatal diagnosis is recommended for at risk pregnancies and mass spectrometry offers speed and quantitation.

Evaluation of Patients Referred to Children's Medical Center Laboratory for Diagnosis of Mucopolysaccharidoses: Eight Years' Experience from Iran

Mucopolysaccharidoses (MPSs) are rare lysosomal storage diseases, resulting from deficiencies of enzymes responsible for Glycosaminoglycans (GAGs) degradation. This leads to accumulation of GAGs in tissues and their excretion in urine, with a wide variety of manifestations. Early diagnosis of MPSs is strictly recommended due to available therapy that can slow down disease progression during the early ages. This study aimed to evaluate patients with suspected MPS referred to Children's Medical Center laboratory over eight years. We also evaluated the usefulness of urine GAG as a screening test for identification of such patients. A total of 1414 patients (40% female, 60% male, with mean age 3.1 ± 4.1years) have participated in this study. The urinary GAG analysis (uGAG) was performed by 1, 9-dimethyl-methylene blue (DMMB) and Berry spot test (BST). All patients with positive and mild positive results or with disease-related symptoms were evaluated in terms of definitive diagnosis, received treatments, morbidity, and mortality rate. In 407 (36.5%) patients uGAG were positive or mild positive, of which 26.3% suffered from one of the types of MPSs, 28.5% suffered from other diseases, 32.9% were undiagnosed, 12.3% were apparently healthy, and 19 died. The negative predictive value of uGAG test in our study was 100%. About 21% of MPSs patients received enzyme replacement therapy, while four patients underwent stem cell transplants. The rest received supportive care. We concluded that a combination of DMMB and BST methods has acceptable sensitivity for screening suspicious MPS patients.

Mucopolysaccharidoses diagnosis in the era of enzyme replacement therapy in Egypt

BACKGROUND

Undegraded glycosaminoglycans (GAGs) induced by deficiency of enzymes are the primary cause of mucopolyscchardoses. Mucopolysacchardoses (MPS) are a group of rare lysosomal storage diseases (LSD). The quantification of a specific enzymatic activity is needed for accurate diagnosis. The objectives of this work were: first, to continue the study of mucopolysacchardoses disease in Egypt after the start of using the enzyme replacement therapy (ERT). Second, to define the commonest types among our population after 18 years experience with the disease. Third, to compare the different MPS types' distribution, diagnosed after the start of the ERT, to identify the impact of using ERT on the number and type of diagnosed patients.

METHOD

Urinary GAGs were measured for all referred cases followed by two-dimensional electrophoretic separation for cases with high levels of GAGs; the specific enzyme activity was assayed for each type depending on the abnormal electrophoretic pattern obtained. Clinically suspected cases of Morquio syndrome were directly subjected to measuring the specific enzyme.

RESULTS

Out of 1448 suspected cases, 622 (42.9%) MPS patients were diagnosed revealing the following distribution: MPS I (172, 27.7%), MPS II (57, 9.1%), MPS III [(177, 28.5%: 134 type B and 43 types A, C or D)], MPS IVA (124, 19.9%), MPS VI (90, 14.5%) and MPS VII (2, 0.3%). MPS III was the most commonly diagnosed type followed by MPS I and MPS IVA. MPS IVA represented the most common type receiving treatment, followed by MPS I, MPS II and MPS VI.

CONCLUSION

The presence of treatment encouraged the affected families and physicians to seek diagnosis. MPS III was the commonest type among our studied group after 7 years of diagnosis, while MPS IVA was the commonest type receiving treatment.

Four novel mutations in the N-acetylgalactosamine-6-sulfate sulfatase gene among Egyptian patients with Morquio A disease

Morquio A disease (Mucopolysaccharidosis IVA, MPS IVA) is an autosomal recessive lysosomal storage disorder caused by deficient activity of the enzyme N-acetylgalactosamine-6-sulfate sulfatase (GALNS) encoded by the GALNS gene. This deficiency leads to a decreased ability to degrade the glycosaminoglycans (GAGs) keratan sulfate and chondroitin 6-sulfate, thereby causing their accumulation within the lysosomes and consequently prominent skeletal and visceral abnormalities. Clinical evaluation and biochemical GALNS enzyme activity determination were carried out for the patients from four unrelated Egyptian families. Mutational analysis was performed to PCR products by sequencing of the 14 exons and exon-intron boundaries of GALNS gene for the 4 patients. Sequence analysis revealed four novel mutations; three nonsense mutations (p.Q12X, p.Q220X, p.Y254X) and one missense mutation, p.D40G. All four patients were offspring of consanguineous marriages and were homozygous for the corresponding mutation. The activity of the GALNS enzyme was below normal reference range in all of them. The p.Q12X and p.Y254X were associated with severe MPS IVA phenotype. Molecular analysis of GALNS gene revealed four novel mutations in four different Morquio A Egyptian patients.

Development of a rapid method for simultaneous separation of hyaluronic acid, chondroitin sulfate, dermatan sulfate and heparin by capillary electrophoresis

This study reports the use of diethylenetriamine as background electrolyte for the simultaneous separation of hyaluronan acid, chondroitin sulfate, dermatan sulfate and heparin. The analytes were baseline separated by using an uncoated fused silica capillary at 37°C with a run time of 23min. The migration order, with hyaluronan acid at first and heparin at last, was related to the sulfation degree. The effect of salt concentration on resolution and migration order was also investigated. The developed method was applied to the simultaneous determination of hyaluronan acid and chondroitin sulfate in mouse plasma. Interferences in plasma were removed by protein precipitation and glycosaminoglycans were further purified by ethanol precipitation. The method was validated over the concentration range from 50 to 600μg/mL for hyaluronan acid and 500 to 6000μg/mL for chondroitin sulfate in mouse plasma. Results from assay validations showed that the method was selective and robust.