Investigations of micro-organic brain damage (MOBD) in heterozygotes of metachromatic leukodystrophy

Extremely low arylsulfatase A enzyme activity does not necessarily cause symptoms: A long‐term follow‐up and review of the literature

Metachromatic leukodystrophy (MLD) is an autosomal recessive lysosomal storage disease caused by deficiency of arylsulfatase A (ARSA). Heterozygous carriers of disease‐causing variants and individuals harbouring pseudodeficiency alleles in the ARSA gene exhibit reduced ARSA activity. In the context of these genotypes, low ARSA activity has been suggested to lead to an atypical form of MLD or other neurological abnormalities, but data are limited. The aim of our study was to analyse the impact of low ARSA activity in two subjects who are heterozygous for the ARSA pseudodeficiency allele and a disease‐causing variant. Biochemical testing included ARSA activity measurements and urinary sulfatide analysis. Biochemical data of a large cohort of MLD patients, heterozygotes, pseudodeficient individuals and healthy controls were analysed. MRI was performed at 3T using T1‐ and T2‐weighted sequences and MR spectroscopy. We present two long‐term follow‐ups who are heterozygous for the ARSA pseudodeficiency allele and a disease‐causing variant in the ARSA gene in cis. The two related index cases exhibit markedly reduced ARSA activity compared to controls and heterozygous carriers. The neurological evaluation and MRI do not reveal any abnormalities. Our data underline that extremely low enzyme activity due to a pseudodeficiency allele and a disease‐causing variant in the ARSA gene even in cis does not lead to clinical symptoms or pre‐symptomatic MRI changes suspicious for MLD. The review of literature corroborates that any association of low ARSA activity with disease features remains questionable. It seems important to combine the measurement of ARSA activity with elevated sulfatide as well as genetic testing, as done in current newborn screening approaches. Heterozygosity for metachromatic leukodystrophy and an arylsulfatase A pseudodeficiency allele does not cause neurological or neuropsychiatric features.

A homozygote for the c.459+1G>A mutation in the ARSA gene presents with cerebellar ataxia as the only first clinical sign of metachromatic leukodystrophy

Metachromatic leukodystrophy (MLD) is a rare lysosomal disorder caused by deficient activity of arylsulfatase A or the lack of saposin B, which results in the accumulation of sulfatide in the oligodendrocytes and in the Schwann cells. Three main clinical types of MLD can be distinguished according to the age of onset and the dynamics of clinical outcome: late infantile, juvenile, and adult. We report on a case of late infantile MLD presenting with cerebellar ataxia as the only first clinical sign preceding even changes in white matter visible in MR imaging. The diagnosis was made on the basis of successive MRI, characteristic of demyelination, which developed in the course of the disease, and on the results of the following biochemical and molecular analyses. Very low residual activity of arylsulfatase A was demonstrated in blood leukocytes and the patient was a homozygote for a common mutation c.459+1G>A in the ARSA gene. Since cerebellar ataxia is a relatively common but unspecific neurological symptom in toddlers, it is recommended that MLD be considered as part of the differential diagnosis even if the initial neuroimaging studies are normal and ataxia is the only clinical symptom of the disease.

Adult metachromatic leukodystrophy treated by allo-SCT and a review of the literature

Five patients with adult-onset metachromatic leukodystrophy (MLD) underwent allo-SCT. Conditioning was reduced in intensity and grafts were obtained from voluntary unrelated donors. All but one graft were depleted of T-lymphocytes. Patient age at transplantation varied from 18 to 29 (median, 27) years. Two patients rejected their graft and MLD progressed. The recipient of the unmanipulated graft converted to complete donor chimerism with normalization of arylsulphatase A (ARSA) levels. Despite ARSA normalization, he deteriorated. Another patient was a mixed chimera. Following escalated doses of donor lymphocyte infusions he converted to complete donor chimerism. His levels of ARSA correlated positively with the percentage of donor cells and MLD was not progressive. The fifth patient died after 35 days from complications associated with GVHD. We conclude that results of allo-SCT in symptomatic MLD patients are poor. However, allo-SCT may stop progression of MLD in selected patients.