Clinical Background

Spinal muscular atrophy (SMA) is a neuromuscular disorder characterized by degeneration of the anterior horn cells in the spinal cord, leading to symmetrical muscle weakness and atrophy. SMA is usually classified into four clinical types based on the age of onset and the highest motor function achieved. The progressive loss of motor neurons causes increasing muscle weakness and, ultimately, muscle wasting. The neck and trunk muscles are often affected first, followed by the muscles of the legs and arms, and finally the rib-associated muscles that support breathing.

What causes SMA?

SMA is an autosomal recessive disease, with an estimated incidence of 1 in 10,000.

The disease is inherited from parents.

One in 35 people carries the defective gene without symptoms. They are not affected because the other, well-functioning member of their gene pair ensures proper functioning.

If both parents carry the gene defect, there is a 25% chance that both will pass on the affected gene to their offspring, so that their child will develop the disease.

SMA is caused by insufficient amounts of the survival motor neuron (SMN) protein in cells. The SMN protein ensures that motor neurons, which are responsible for transmitting signals from the brain to muscle cells, remain healthy. If the SMN protein is missing or present at very low levels, the motor neurons die and the muscles atrophy.

The SMN protein is mainly produced by the SMN1 gene. In SMA patients, there is no working copy of the SMN1 gene from which the SMN protein can be produced. People with one copy of SMN1 (one in 35 people) are SMA carriers: they do not have symptoms of SMA. However, a carrier couple may have children with SMA.

The very similar SMN2 gene also plays a role in SMA. SMN2 produces mostly non-functional SMN protein and small amounts of functional SMN protein.

The number of copies of SMN2 varies between individuals in the population. In SMA patients, the more copies of SMN2 they have, the less severe their symptoms.

If you want to know for yourself whether you are an asymptomatic carrier

92-97% of SMA carriers can be identified by the presence of a single copy of SMN1. Carrier screening can detect this abnormality.

However, approximately 3-8% of SMA carriers have two copies of SMN1, but one may be functional and the other defective, or they may have two copies of SMN1 on one chromosome and 0 on the other (2+0). Gene copy number analysis cannot differentiate between "1+1" and "2+0" (silent carriers) arrangements. Both situations are simply detected as having two copies of SMN1, leading to false negative results. Therefore, a patient who undergoes screening cannot be 100% certain that they are carriers.

SMA carrier screening is best performed before pregnancy.

It can only be requested during pregnancy up to 13 weeks 0 days, as this is when there is enough time to perform all the necessary tests. During pregnancy, if the mother is found to be a carrier, the father should also be tested immediately. If both members of the couple are carriers, invasive genetic testing (amniotic fluid sampling) is required to assess the fetus's involvement.

SMA Carrier Screening

As a separate examination 45,000 HUF
(The price is for one parent.)

Newborn screening tests

Every newborn undergoes the state-mandated biochemical screening on the 3rd day of life. At this time, a small puncture is made on the baby's heel, from which a few drops of blood are obtained; the test itself is performed from this sample. This makes it possible to detect 26 (plus 2, see below) so-called metabolic diseases early. These are very rare diseases, and a significant part of the screening tests end with a negative result. Nevertheless, screening is mandatory because these 26 diseases can be treated in some way - with diet, medication, etc. - or the serious outcome can be prevented. In addition to the 26 metabolic diseases, every baby in our country has been screened for the most common genetic defect that causes the disease cystic fibrosis since 2021; and since December 2022, new parents can request a screening for spinal muscular atrophy (SMA) in their child.

Have you heard of our myNewborn test?

The myNewborn test is a genetic test based on a modern methodology, the main purpose of which is to supplement the mandatory newborn screening. It is recommended for newborns, infants and young children (typically before the age of 6).

The main differences are as follows:

• The newborn screening test is performed using a biochemical method, measuring the metabolic products circulating in the blood (i.e. the substances produced as a result of biochemical processes in our body). This is “only” a screening test, in case of a positive result, a second, confirmatory (usually genetic) test is always necessary.
• myNewborn is a DNA-based genetic test, so we test the child’s genetic material (DNA). The test is performed using the so-called next-generation sequencing method, which provides modern and reliable results.
• myNewborn is actually a “whole exome sequencing”. The exome is the part of the entire human genetic material (human genome) in which genes encoding proteins are found. The proteins encoded by the genes ensure the development and functioning of our body. The myNewborn test analyzes 407 genes known to cause disease when broken (including 26 metabolic diseases and cystic fibrosis tested in the biochemical screening). The diseases tested in this test typically cause symptoms and signs in early childhood (before the age of 10).