# Japanese experience of newborn screening for lysosomal storage diseases and adrenoleukodystrophy

## TL;DR

Japan has expanded newborn screening to include lysosomal storage diseases and adrenoleukodystrophy, identifying more cases than expected but facing challenges like false positives and unclear genetic variants.

## Contribution

The paper provides a comprehensive survey of expanded newborn screening implementation and outcomes for LSDs and ALD in Japan.

## Key findings

- Expanded NBS identified 101 cases of LSDs and ALD in 733,838 newborns, exceeding estimated prevalence.
- Low positive predictive values and high false-positive rates were observed for Pompe disease, MPS II, and ALD.
- Many ALD cases showed variants of unknown significance in the ABCD1 gene.

## Abstract

Recently, Newborn screening (NBS) has been expanded worldwide to include lysosomal storage diseases (LSDs) and adrenoleukodystrophy (ALD) due to the importance of early diagnosis and early treatment. In Japan, NBS for LSDs, termed expanded NBS, was first implemented in Kumamoto prefecture in 2006 as pilot study. NBS for ALD was subsequently introduced in Aichi prefecture and Gifu prefecture in 2021. Expanded NBS for LSDs and ALD has become more widespread in Japan. In light of this current situation, we considered it is necessary to clarify the usefulness of expanded NBS, prevalence of each disease, challenges encountered. Therefore, we reported the current implementation status of expanded NBS in Japan.

A survey was conducted among physicians responsible for expanded NBS in each target region Japan. The target regions were those that implemented NBS for LSDs and/or ALD for more than one year. The survey items included: the entity conducting expanded NBS, the facilities conducting the tests, the target areas, medical institutions for close examination such as detailed biochemical analysis and/or genetic sequencing, and treatments, types of target diseases, fee for NBS, sample collection methods, testing method, and quantitative data on expanded NBS, retesting, and diagnoses in each area.

Responses were received from nine regions and an organization (CReARID). The total number of 733,838 newborns were screening, with 101 diagnoses: 75 cases of Fabry disease, 10 of mucopolysaccharidosis (MPS) II, 8 of Pompe disease, 5 of Gaucher disease, 2 of MPS I, 1 of ALD, respectively) were diagnosed. More cases were diagnosed with the target disease than the estimated prevalence. In contrast, the positive predictive value was low and false-positive rates was elevated, particularly for PD, MPS II, and ALD, have been attributed to pseudodeficiency alleles and methodological differences. Moreover, variant of unknown significance (VUS) in the ABCD1 gene was detected in many of the patients with suspected ALD.

In Japan, Expanded NBS for LSDs and ALD has become more widespread. Since its implementation, some patients have been diagnosed and received treatment. However, challenges such as pseudodeficiency, indications, testing methods, and VUS that require improvement.