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Complications in the genotypic molecular diagnosis of pseudo arylsulfatase A deficiency
Abstract:
Metachromatic leukodystrophy (MLD) is a severe neurodegenerative disease associated with deficient arylsulfatase A activity. Biochemical confirmation of this disorder has been complicated by a clinically normal but enzymatically deficient variant, pseudo arylsulfatase-A deficiency (PD). The PD mutation is associated with two A-->G transitions in the arylsulfatase A gene. They can be detected simultaneously with a recently developed 3'-mismatch polymerase chain reaction, hence providing a rapid method for genotypic identification and resolving ambiguities of carrier identification based solely on enzyme analyses. However, we now report further genotypic complexities in the molecular diagnosis of PD due to the occurrence of another variant in which only one of the two A-->G mutations of the PD allele was present. This variant confers reduced but readily detectable enzyme activity and behaves as a silent allele in the 3'-mismatch polymerase chain reaction, thus leading to conflicting and erroneous genotype assignments in a family in which both variants and MLD co-exist. The inconsistency was resolved after pedigree validation and further molecular analyses in which the two A-->G mutations were assayed separately with allele-specific oligonucleotides. Because arylsulfatase A analysis is one of the most commonly requested lysosomal enzyme assays and the PD mutant allele frequency is high in the general population, complexities as described in this family may be a recurrent problem that can be solved only with combined enzymatic and detailed molecular analyses.
Insights
Metachromatic leukodystrophy (MLD) diagnosis is complicated by pseudo arylsulfatase-A deficiency (PD). New variants require combined enzymatic and molecular analyses for accurate genetic identification.
Area of Science:
- Biochemistry
- Genetics
- Neuroscience
Background:
- Metachromatic leukodystrophy (MLD) is a severe neurodegenerative lysosomal storage disorder caused by arylsulfatase A (ARSA) deficiency.
- Accurate diagnosis is crucial for patient management and genetic counseling.
- Pseudo arylsulfatase-A deficiency (PD) presents a diagnostic challenge due to a common variant with normal phenotype but reduced enzyme activity.
Observation:
- The PD mutation involves two specific A-->G transitions in the ARSA gene.
- A novel variant with only one A-->G mutation was identified, exhibiting reduced enzyme activity.
- This single-mutation variant acts as a silent allele in standard 3'-mismatch PCR, complicating genotype analysis.
Findings:
- The presence of both PD variants and MLD in a single family led to conflicting genotype assignments.
- Pedigree validation and allele-specific oligonucleotide analysis resolved these diagnostic ambiguities.
- Combined enzymatic and detailed molecular analyses are essential for accurate MLD and PD diagnosis.
Implications:
- The high frequency of the PD allele in the general population suggests these diagnostic complexities may be recurrent.
- Accurate genetic testing is vital for distinguishing between MLD, PD, and carrier states.
- This study highlights the need for advanced molecular techniques to ensure precise diagnosis of ARSA-related disorders.