Distal Spinal Muscular Atrophy

INTRODUCTION

Every child born should be able to fully each and every development milestone. It gives immense joy to the parents and a sense of fulfillment to the child which can be seen when they smile. A disorder at any period starting right from birth is going to make it difficult for the child to survive accomplishing each and every milestone. One such second rare disorder among the children is Distal Spinal Muscular Atrophy.

Distal Spinal Muscular Atrophy or SMA is a rare genetic neuromuscular disorder caused by deficiency of Survival Motor Neuron [SNM] which is essential for normal motor function.

It affects the control of voluntary muscle movements as the motor neuron in the spinal cord is affected.

People affected by this disorder experience proximal weakness and fatigue in almost all cases and muscle weakness of lower and upper limbs.

Often people suffering from the disease don’t experience stiffness of neck, cramps and no sensory or autonomic dysfunction.

This disorder is classified into 4 types namely SMA Type-1, SMA Type-2, SMA Type-3 which is subdivided as SMA-3a and SMA-3b based on before or after 3 years of age and SMA Type-4.

SYMPTOMS

The SMA Type 1 also known as Werdnig Hoffmann disorder exhibits before 6 months of age and the infant never achieves a motor milestone of sitting unsupported.

The child doesn’t survive 2yrs of age due to respiratory malfunction. It is a common type which accounts to about 60% of SMA diagnosis.

Additional subtypes of Type 1 include 1A,1B,1C. 1A is the earliest and severe subtypes of neonates which leads to Joint contractors, severe weakness, hypotonia. The infant survives for <6 months of age.

The infant cannot perform anti-gravity limb movements, no fine motor skills which makes it unable to grasp, no head control, bell shaped chest, difficulty in swallowing due to bulbar weakness.

Due to reflex and impair cough and swallowing, it causes pulmonary infections.

CAUSES

It is caused by autosomal recessive condition were both parents of the individual are the carriers of the gene.

Lack of SMN 1 is caused by chromosome 5 leading to the symptoms.

SMN 2 gene can compensate some functions of SMN 1.

TREATMENT

The disorder affects more than one organ. So multi- dimensional approach to treatment is opted to reduce the severity of the symptoms.

The treatment includes physiotherapy to avoid muscle weakness. The physiotherapist looks for joint power and range. Exercise and activity splinting, taping, orthotics, are performed to avoid further muscle weakness.

Medical treatment: Neuro protective drugs like Kilomole, drugs to improve energy metabolism and drugs affecting gene expression of SMN are used.
Gene Therapy: Viral Vectors are used to replace SMN 1 Gene.
Respiratory Care: Airway clearance therapy is given to prevent pulmonary infections. Suctioning is used when there are excessive secretions with an ineffective cause.

PREVALENCE

1 in 6 – 10000 is affected by SMA with 1 in 35-70 as carrier frequency.

CONCLUSION

With proper diagnosis and preventive measures, the disorder can be identified at an early stage and an effective treatment method can help the patient to reduce the severity of the symptoms.