Adult-onset metachromatic leukodystrophy: a novel genotype with a distinct phenotype

Metachromatic leukodystrophy (MLD) is a lysosomal storage disorder caused by the deficiency of arylsulfatase A (ARSA). Accumulation of sulfatide, substrate of ARSA, in the central and peripheral nervous system causes neurodegeneration, which leads to neurologic and psychiatric symptoms. Adult-onset MLD is the least frequent type of MLD and shows both genetic and clinical heterogeneity. The clinical presentation differs according to pathogenic variants in the ARSA gene. Therefore, establishing genotype-phenotype correlation is crucial for the diagnosis and management of patients with adult-onset MLD.

A family of multiple individuals with adult-onset psychomotor deterioration was assessed. The patients had behavioral disturbances initially, and neurological deficits had developed in the later stages of the disease. The family was analyzed using karyotype analysis, Sanger sequencing, custom next-generation sequencing (NGS) panel of the genes related to dementia, and whole exome sequencing (WES).

Karyotype analysis and NGS dementia panel showed no pathogenic aberration. However, WES analysis revealed heterozygous variants in the ARSA gene: c.542T>G (p.Ile181Ser) and c.661T>A (p.Phe221Ile). Segregation analysis, performed by Sanger sequencing, showed that all individuals with the same clinical findings were compound heterozygous for c.542T>G and c.661T>A substitutions.

The compound heterozygosity of c.542T>G and c.661T>A variants of the ARSA gene cause adult-onset MLD. The genotype detected in the patients was not reported before in the literature. Moreover, the clinical course of the patients followed a similar pattern with dominantly psychiatric symptoms at the initial stage of the disease, indicating a distinct phenotype caused by the two pathogenic variants of the ARSA gene.