Relative Frequency of Metachromatic Leukodystrophy in Egypt: A Reference Laboratory Report

BACKGROUND: Metachromatic leukodystrophy (MLD) is an autosomal recessive hereditary neurodegenerative disease caused by a deficiency in arylsulfatase A (ARSA) activity and belongs to the group of lysosomal storage diseases. A biochemical diagnosis of MLD is based on determining the residual ARSA activity in leukocytes, skin fibroblasts, and urine. This study documents our biochemical experience and estimates the relative frequency of MLD over 21 years (2001-2022). METHODS: This study analyzed 4357 suspected cases of MLD in Egypt. The ARSA activity was spectrophotometrically determined in leukocytes in all the referred cases. RESULTS: Of these 4357 referred cases, 577 (13%) possessed decreased ARSA activity, less than 10% of the low normal range (50-200 micromole/gram protein/hour (μmol/g protein/h), and 104 cases were diagnosed as having a pseudodeficiency in enzyme activity (<20-50% of low-normal ARSA activity). The prevalence of MLD was 1.6/100,000. CONCLUSIONS: A diagnosis of MLD in Egypt is based on enzyme activity levels and clinical suspicion; molecular analysis was performed in a few cases.