Assessment of Spinal Muscular Atrophy Carrier Status by Determining SMN1 Copy Number Using Dried Blood Spots.

Yogik Onky Silvana Wijaya,Dian Kesumapramudya Nurputra,Emma Tabe Eko Niba,Seiji Yamaguchi,Yoshihiro Bouike,Sunartini Hapsara,Jamiyan Purevsuren,Mawaddah Ar Rochmah,Hisahide Nishio,Nur Imma Fatimah Harahap,Masakazu Shinohara,Cempaka Thursina

doi:10.3390/ijns6020043

Abstract

Spinal muscular atrophy (SMA) is a common neuromuscular disease with autosomal recessive inheritance. The disease gene, SMN1, is homozygously deleted in 95% of SMA patients. Although SMA has been an incurable disease, treatment in infancy with newly developed drugs has dramatically improved the disease severity. Thus, there is a strong rationale for newborn and carrier screening for SMA, although implementing SMA carrier screening in the general population is controversial. We previously developed a simple, accurate newborn SMA screening system to detect homozygous SMN1 deletions using dried blood spots (DBS) on filter paper. Here, we modified our previous system to detect the heterozygous deletions of SMN1, which indicates SMA carrier status. The system involves a calibrator-normalized relative quantification method using quantitative nested PCR technology. Our system clearly separated the DBS samples with one SMN1 copy (carrier status with a heterozygous deletion of SMN1) from the DBS samples with two SMN1 copies (non-carrier status with no deletion of SMN1). We also analyzed DBS samples from SMA families, confirmed SMA in the affected children, and determined the carrier status of their parents based on the SMN1 copy number. In conclusion, our system will provide essential information for risk assessment and genetic counseling, at least for SMA families.

Highlights

Spinal muscular atrophy (SMA) is an autosomal recessive and progressive neuromuscular disease characterized by muscle weakness and atrophy that results from the degeneration of motor neurons in the spinal cord [1]
We developed a new simple, accurate, and inexpensive system for determining the Survival Motor Neuron 1 (SMN1) copy number and SMA carrier status
The SMN2 amplification curves of Patients 1, 2, 3, and 4 showed steep rises at ~10 cycles in the second round PCR, similar to the controls (Figure S1). These results indicated that these patients carried homozygous SMN1 deletions, confirming the diagnosis of SMA

Summary

Introduction

Spinal muscular atrophy (SMA) is an autosomal recessive and progressive neuromuscular disease characterized by muscle weakness and atrophy that results from the degeneration of motor neurons in the spinal cord [1]. The incidence of SMA is 1 in 6000 to 10,000 live births [1], and the carrier frequency is 1 in 40 to 60 in the general population [1]. Survival Motor Neuron 1 (SMN1) has been identified as the SMA-causing gene [2]. SMN1 is absent (or homozygously deleted) in ~95% of SMA patients and deleteriously mutated in some of the remaining patients [2,3]. A deletion test for SMN1 is the first-tier evaluation for SMA diagnosis. SMA phenotypes are classified by onset age and achieved motor milestones. Patients with SMA type 1 develop symptoms in the first 6 months after birth, never achieve the motor milestone of sitting independently, and have a life expectancy of less than 2 years without respiratory support [4]. SMA type 1 constitutes the largest group of SMA patients, and it is the most frequent genetic cause of death in infants

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