Genetic Disease – Spinal Muscular Atrophy (SMA)
Spinal muscular atrophy (SMA) is an inherited disease that affects an infant’s muscular activity. Voluntary muscles are driven by motor neurons. Children with SMA are missing a gene that is required to produce certain proteins involved in motor neuron development. Without this protein, the nerves shrink and ultimately atrophy. Without motor neuron innervation, the muscles then degenerate or atrophy. Infants with Type I SMA will have difficulty raising their head, kicking their legs and even smiling. The child’s brain is unaffected and children with SMA are of normal intelligence. They are aware of their difficulties. Normal body functions like swallowing and breathing are also affected. Without the ability to swallow, a feeding tube is required to prevent starvation. With progressive atrophy, the muscles involved in breathing are affected and a parent must make the difficult decision to place the child on permanent ventilation for life support. The average lifespan of a child with SMA Type I is only 8 months of age, with 80% dying by the age of one, and the majority thereafter dying by two years of age.
SMA is an autosomal recessive genetic disease. One in 35 Caucasians carries the SMA gene; one in 53 Asians and one in 66 African Americans carry the SMA gene. The disease can only be acquired if both parents carry the gene and then the risk of having a child with SMA is 1 in 4. The 1 in 35 simply carrying the recessive gene alone will not have the disease or any associated symptoms. The statistical odds that both parents carry SMA = 35 x 35 = 1 in 1225 couples.
Although the odds that both parents carry the gene is low at 1 in 1225, the Fertility Centers of New England strives to reduce this risk to zero. The Centers’ goal is not just to achieve pregnancy but to achieve a healthy pregnancy and child. To undergo the rigors of fertility treatment without awareness of the genetic risk can be stressful and does not take advantage of the current screening technologies. From a simple saliva sample, patients can be pre-screened and be fully aware of their genetic risks. Those couples shown to both be carriers of an autosomal recessive trait, including SMA and others, may proceed with preimplantation genetic diagnosis (PGD) of their embryos. Healthy embryos diagnosed not to carry the gene are then transferred for pregnancy.