What is Werdnig-Hoffmann disease?

Werdnig-Hoffmann disease is a type of spinal muscular atrophy (SMA) now called spinal muscular atrophy type 1 (SMA1). It is a genetic disorder in which the motor neurons degenerate. This is the most severe type of SMA. The onset age is from birth to 6 months (infants). It is inherited in an autosomal recessive pattern. The major symptoms include muscle weakness, poor muscle tone (hypotonia) and lack of motor development because of which the babies suffering from this are sometimes referred to as “floppy babies”. They have difficulties with swallowing and sucking, which affects feeding and consequently weight gain, and also breathing. These babies also have difficulty in sitting up straight without support and are unable to lift their heads. In spinal muscular atrophy, the weakening of muscles is central, therefore infants have more difficulty raising their arms or legs but can move their fingers and toes easily. This disease is very rare and equally prevalent in males and females.

SYMPTOMS

In Werdnig-Hoffmann, infants experience severe weakness before 6 months of age. Apart from muscle weakening and poor muscle tone, the infants also experience twitching (fasciculation) of the tongue, abnormal flexibility of the joints (hypermobility), and an increased susceptibility to respiratory infections. The muscles of the face are not affected initially. There seems to be no problems with cognitive development.

If the babies are untreated or undiagnosed, then they do not survive beyond two years of age. Therefore, screening for SMA 1 has become necessary at the time of birth, so that the proper medical and psychological support can be provided to the infant and the parents.

As the disease progresses, it can slowly spread to the extremities to the point where all the voluntary muscle are affected except the eyes. The rate of progression varies for each infant. Eventually it can lead to respiratory and bowel problems, which can cause problems with breathing and swallowing. The food might enter the lungs due to this and can cause choking.

CAUSES

Werdnig-Hoffmann disease is caused due to genetic factors but the specific cause remains unknown. It seems that the SMN 1 gene, which produces a protein essential for proper motor functioning, undergoes mutation and produces a defective protein. Other factors which can cause spinal muscular atrophy are the deletion of gene NAIP (neuronal apoptosis inhibitory protein) and SMN 2.

Spinal muscular atrophies are inherited in an autosomal recessive pattern. Therefore, an infant will suffer from this disease only if s/he receives a pair of the recessive genes, one from each parent, the chances of which are 25%.

DIAGNOSIS

The disease can be diagnosed by DNA testing to check for the deletion in survival motor neuron 1 (SMN1) on chromosome 5. Other tests which can be done, but are not necessary are an electromyogram (EMG) or muscle biopsy. Genetic testing, carrier testing and prenatal testing is also available to identify at-risk babies. The genetics behind this disease are quite complex and identifying it through carrier testing is a difficult process.

TREATMENT

Werdnig-Hoffmann disease doesn’t have one specific treatment, rather a group of treatments, each targeted at a specific symptom. Several specialists are required to provide support with breathing, feeding and muscle movement. The type of intervention used will vary according to the severity of the disease in the infants.

Breathing support can be offered through invasive and non-invasive techniques. Non-invasive techniques include intermittent positive pressure ventilation to provide comfort, manage acute infection or to rectify night time hyperventilation. But this method is not suitable for infants with severe muscle weakness of the mouth and throat, and for infants less than 6 months of age. Invasive techniques include a tracheotomy, in which a tube is inserted into the trachea by surgery. This is a much long-term solution.

A gastrostomy is the treatment option for feeding difficulties. In this procedure, a tube is directly inserted into the stomach through a surgical opening.

Apart from these treatment option, physical and occupational therapy is also used to help with body movements and circulation. The parents must explore and discuss all the possible treatment options and choose the one most suitable for their infant. Additional care for the health and well-being for the child as well as emotional support for the parents is necessary.

PREVALENCE

It is a rare disorder that affects males and females equally. About 80% of all spinal muscular atrophies are Werdnig-Hoffmann disease.

CONCLUSION

The disease prognosis for children is very poor. If it goes undiagnosed or untreated, they won’t survive for more than two years. A comprehensive treatment plan is required to deal with the various symptoms that the disease brings. It cannot be cured but can be managed using the right treatment plan.

REFERENCES

• https://healthjade.net/werdnig-hoffmann-disease/#Werdnig_Hoffmann_disease_diagnosis
• https://www.sciencedirect.com/topics/nursing-and-health-professions/werdnig-hoffmann-disease
• https://rarediseases.org/rare-diseases/werdnig-hoffmann-disease/