Table of Contents
following table describes the general disease onset, incidence rates, survival and general characteristics for each of the different types of SMA.
event is defined as death or at least 16 hours per day of required ventilation support for breathing for 14 consecutive days in the absence of acute
reversible illness or perioperatively.
SMA Type 1
SMA Type 1 is a lethal genetic disorder characterized by motor neuron loss and associated muscle deterioration,
resulting in mortality or the need for permanent ventilation support before the age of two for greater than 90% of patients. SMA Type 1 is the leading genetic cause of infant mortality. SMA
Type 1 accounts for approximately 60% of all new SMA cases. Symptoms of SMA Type 1 include:
- hypotonia, which is also known as "floppy baby syndrome" and is characterized by abnormal limpness in the neck and limbs;
- muscle weakness, particularly in the legs;
- poor head control;
- abdominal breathing, also known as diaphragmatic or belly breathing, which is characterized by breathing through the contracting of
the diaphragm rather than the chest;
- bulbar muscle weakness, which is exhibited by a weak cry, difficulty swallowing and aspiration; and
- the inability to sit unsupported.
an independent, peer-reviewed natural history study published by the American Academy of Neurology on SMA Type 1 in 2014, or the Finkel 2014 Study, the authors observed that
the life expectancy of a child with SMA Type 1 is, for a majority of patients, less than two years. The following chart presents the percentage of children with SMA Type 1 that die or
require at least 16 hours per day of ventilation support for breathing at varying ages for 14 consecutive days in the