SMARD stands for Spinal Muscle Atrophy with respiratory distress. It is also known as SMARD1 or Distal Spinal Muscle Atrophy(DSMA1). It is a progressive motor neuron disease that currently has no treatment or cure.
How does a child "get" SMARD?
SMARD is genetic disease that is inherited in a recessive pattern. This means that both parents must be carriers of the gene mutation and each parent must pass a copy of the mutation on for the child to affected. This means that every time two carriers have a baby, there is a 1 in 4 or 25% chance they will have an affected baby (see diagram below). The mutations that cause SMARD are located on the IGHMBP2 gene. Each child usually has a unique combination of gene mutations, which is why there can be variability in onset and presentation as well as severity of disease.
How does SMARD differ from SMA?
SMARD and SMA are similar in the fact that they both affect the lower motor neuron cells of the spinal cord that control voluntary muscle activities like walking, talking, breathing and swallowing. Both are often said to be like "ALS in babies". The main differences are that SMA (which can range from type 1-4) is caused by mutations in or the absence of the SMN1 gene and SMARD is caused by mutations in the IGHMBP2 gene. SMA typically causes weakness in the core first and the baby or child may present as "floppy" or hypotonic (low muscle tone) and eventually develop respiratory compromise over time. SMARD typically causes diaphragm paralysis resulting in severe, acute respiratory distress first and then begins to lose muscle tone in the distal muscles (usually the legs more than the arms). Simply put, SMA usually presents as a "floppy" baby who gradually develops respiratory distress and SMARD presents as a baby in respiratory distress that gradually becomes "floppy". SMA is the #1 genetic killer of infants. 1 in 40 people are carriers of SMA. SMARD is much rarer. It is unknown how many people are carriers of SMARD at this time.
What happens in SMARD?
SMARD causes diaphragm eventration and paralysis, which leads to respiratory distress in the infant. This usually occurs suddenly in what seems to be an otherwise healthy baby. The typical age of onset is between 6 weeks and 6 months of age, however this can vary. Once the diaphragm is paralyzed, the infant must depend on their accessory muscles to breathe. As the disease progresses, these muscles weaken and the infant eventually becomes dependent on the ventilator to breathe. Cognitive function remains unaffected in SMARD. SMARD also can cause:
-decreased fetal movement while in utero
-IUGR (low birth weight)
-preterm birth(born before 37 weeks gestation)
-feeding difficulties and poor weight gain
-muscle weakness(usually greater in the lower extremities and distal muscles)
-elevated heart rate
-foot drop or clubbed feet
What is the prognosis of SMARD?
Many children die in the first year of life, often in their sleep or from a respiratory illness. Almost all who are living with SMARD past 1 year of age require a tracheostomy and are ventilator and wheelchair dependent. The degree of muscle weakness varies from child to child. All children with SMARD are at severe risk of life threatening complications whenever they contract a respiratory virus.
How common is SMARD?
SMARD is extremely rare. It has been diagnosed in approximately 100 children in the world, but the exact number of cases is unknown. It is considered an orphan disease as a result. Information and resources are hard to find, and there are only a handful of research articles available for review.