Types and how they differ
The type is determined by the age at which the first signs appear and by the maximum motor skill the person has achieved. The earlier the debut, the more severe the course, and vice versa. The number of copies of the similar SMN2 gene plays an important role: it partially compensates for the lack of protein, and the more copies, the milder the form. This is why the same mutation can look different in different families.
- Type 1 - debut before 6 months, the child does not sit up independently
- Type 2 - debut 6–18 months, the child sits but does not walk
- Type 3 - debut after 18 months, walking is mastered, weakness increases later
- Type 4 - onset in adulthood, mild course
- SMN2 gene copy number influences severity
How it manifests itself
In infants, attention is paid to pronounced lethargy: the child does not hold his head up well, lies with his hips apart, does not push off with his legs, and raises his arms with difficulty. Characterized by twitching of the tongue, a weak cry and paradoxical breathing, when when inhaling, the stomach protrudes and the chest sinks. In older children and adults, weakness is first noticeable in the muscles of the hips and shoulder girdle: it is difficult to get up from the floor and from a chair, climb stairs, or raise your arms. Over time, scoliosis and joint contractures develop.
- Severe muscle flaccidity in an infant
- Loss or delay of motor skills
- Weakness in the hips and shoulders, difficulty standing up
- Tongue twitching, finger trembling
- Weak cough, frequent respiratory infections
- Scoliosis, chest deformities, contractures
- Problems with sucking and swallowing
Diagnostics
The main method is genetic analysis: in most patients, the loss of both copies of the SMN1 gene is detected, and the number of SMN2 copies is simultaneously calculated, which is important for prognosis and choice of therapy. If the picture is atypical, additional electroneuromyography and biochemical tests are performed. Muscle biopsy is rarely required today. In many countries, the disease is included in neonatal screening programs because treatment started before the onset of symptoms produces the best results. The family must be offered genetic counseling.
- Molecular genetic analysis of the SMN1 gene
- Determination of the copy number of the SMN2 gene
- Electroneuromyography with an unclear picture
- Creatine phosphokinase and biochemical blood test
- Spirometry and assessment of night breathing
- X-ray of the spine for scoliosis
- Genetic counseling for parents
Treatment and support
Drugs have appeared that affect the cause of the disease: they increase the amount of missing protein and are prescribed only by a neurologist in a specialized center according to strict indications. Such therapy does not replace comprehensive support. Rehabilitation is aimed at preventing contractures and scoliosis, maintaining mobility and skills, selecting orthoses and technical aids. Monitoring of breathing, training in coughing techniques, vaccination against respiratory infections and nutritional monitoring are mandatory. In case of scoliosis, an orthopedist is involved. The program is built individually and revised as the child grows.
- Pathogenetic therapy is prescribed by a neurologist at a specialized center
- Regular physical therapy and positioning
- Orthoses, corset, verticalization, wheelchair according to age
- Breath control, cougher, non-invasive ventilation as indicated
- Food with sufficient caloric content, if necessary - tube feeding
- Vaccination and prevention of respiratory infections
- Observation by an orthopedist for scoliosis and contractures
Inheritance and family planning
The disease is inherited in an autosomal recessive manner: a child becomes ill if he received the altered gene from both parents. The parents themselves are healthy and often do not know about the carrier state. For a couple who already has a child with this diagnosis, the risk is repeated with each pregnancy, so it is important to discuss the situation with a geneticist before planning the next child. Carrier status can be checked with a blood test, and during pregnancy there are prenatal diagnostic methods.
- Autosomal recessive mode of inheritance
- Carrier parents are usually completely healthy
- The risk is repeated with every pregnancy
- Carrier testing is available to both partners
- Prenatal diagnosis is discussed with a geneticist
- Consanguineous marriage increases risk