Host:

There are people in the world who suffer from motor neuron degeneration due to genetics. After onset, they gradually lose strength. The condition gets worse over time. This is spinal muscular atrophy.

Today we've invited Dr Sophelia Chan, Honorary Consultant, Department of Paediatrics and Adolescent Medicine, Hong Kong Children's Hospital to tell us about it.

Hello, Dr. Chan. Can you share this with us? What kind of disease is this actually?

Dr Sophelia Chan:

Spinal muscular atrophy is a genetic neuromuscular disease. The disease can cause muscle weakness and muscle atrophy in children.

Host:

Is this disease related to other similar muscular dystrophy diseases that also cause muscle weakness or symptoms of mobility impairment?

Dr Sophelia Chan:

You are absolutely right. Because when the skeletal muscle is affected, it will cause poor motor ability. Depending on the severity, if it's serious, some children will never be able to sit, some even can't turn over.

Host:

I came across some information stating that the age of onset for this disease can vary significantly. Does the severity also vary greatly depending on the age of onset?

Dr Sophelia Chan:

You are quite right. In fact, the earlier the onset of the disease, the more severe the child's symptoms are. In fact, spinal muscular atrophy or SMA has four types. We call them SMA Type 1, Type 2, Type 3 and Type 4.

For the most severe type 1, symptoms usually occur within the first six months. In the most serious situation, symptoms could happen soon after the baby is born. We may note that the baby has some difficulty breathing and decreased movement in the arms and legs, necessitating admission to the neonatal care unit. Other children with SMA Type 1 might have symptoms a little later, perhaps two or three months, or even four to six months after birth. Children with SMA Type 1 are the most seriously affected because their condition deteriorates very quickly. In the second half of the first year, many children will already have obvious difficulty swallowing and require tube feeding. They also have difficulty breathing, necessitating a non-invasive ventilator to assist their breathing, and their arm and leg movements are poor.

In the past when there was no treatment, many children, more than 80% of them in Hong Kong and around the world, did not survive past the age of two.

Host:

Patients may experience difficulty in breathing or develop pneumonia, leading to death. But why does this muscular dystrophy lead to such a serious situation?

Dr Sophelia Chan:

You've asked a good question. Because when we breathe, in addition to the lung's expansion, we need our breathing muscles. During inhalation, our muscles help expand the ribs in the chest. When we exhale, these muscles contract. Children with seriously affected respiratory muscles can't breathe on their own for inhalation and exhalation. Initially, they may be able to use their diaphragm for assistance. At a later stage, this effort may not be strong enough, necessitating the use of external support, which is a ventilator.

For ventilators, we have a non-invasive one. It's used through a face mask which provides ventilation support to aid their breathing. There is also invasive respiratory support. The child will have a tracheostomy opening to help them breathe through a ventilator. So, breathing problem is very serious. Because oxygen is vital to all organs in our body. Any problem in breathing can therefore be life-threatening.

As for eating, in fact, it can also affect the lungs. Because when a child is eating, if their oral muscles are weak, he or she can choke easily. When they choke, and cannot effectively cough up the choked food, it can lead to aspiration pneumonia. This directly affects the lungs, damaging the lung function due to aspiration pneumonia.

Host:

Doctor, you mentioned at the beginning that it's a genetic disease. I understand it is of recessive inheritance. What does that mean?

Dr Sophelia Chan:

In recessive inheritance, the child needs to have a pair of abnormal genes. For the gene that causes SMA, it is located on the fifth chromosome, only if there is an abnormal gene from the father, and an abnormal gene from the mother, with both genes having mutations, or exon deletion, this disease will occur.

Host:

But how common is it?

Dr Sophelia Chan:

Actually, SMA is a rare disease. We know that the carrier rate is about one in 50 to 60 people. But for the carriers, we know both parents need to be carriers, then there is a one-in-four chance for their child to have this rare disease SMA. Given these probabilities, we can estimate that likely among ten thousand people, only one child will be affected by this situation.

Host:

So, is newborn screening very important?

Dr Sophelia Chan:

Yes, Janet, it is extremely important. In Hong Kong, we now have newborn screening for SMA. The sooner we discover it, the earlier we can start treatment. Starting the treatment during the pre-symptomatic stage or the early stages of symptoms gives the best clinical effect. There may even be a chance for the child's development to progress normally.

Host:

Thank you, doctor, for sharing today. Let's conclude here. Goodbye.