SNP Shot: Genomic Insights

Infantile neuroaxonal dystrophy (INAD) is a condition that mainly impacts the nervous system. Babies with INAD typically appear normal at birth. However, between 6 and 18 months of age, they start showing delays in reaching developmental milestones involving movement and thinking, such as crawling or talking. Over time, they lose skills they had already learned (developmental regression). In some instances, the signs of INAD may not become apparent until later in childhood or even the teenage years, and the condition progresses more slowly.

Children affected by INAD experience increasing difficulty with movement. Initially, their muscles tend to be weak and "floppy" (hypotonia), but they gradually become very stiff (spasticity). Eventually, these children lose the ability to move on their own. Muscle weakness can also lead to feeding difficulties and breathing problems, increasing the risk of frequent infections like pneumonia. Some children with INAD also experience seizures.

Common features of INAD include rapid, involuntary eye movements (nystagmus), misaligned eyes (strabismus), and vision loss resulting from the breakdown (atrophy) of the optic nerve, which carries visual information to the brain. Hearing loss may also occur. Individuals with INAD also experience a progressive decline in cognitive abilities (dementia), eventually leading to a loss of awareness of their surroundings.

A defining characteristic of INAD is the formation of swellings called spheroid bodies within the axons of nerve cells (neurons). Axons are the fibers that extend from nerve cells and transmit signals to muscles and other neurons. In some individuals with INAD, there's an unusual buildup of iron in a specific area of the brain called the basal ganglia. The connection between these features and the symptoms of INAD is currently not understood.

Inheritance:

INAD follows an autosomal recessive inheritance pattern. This means that an individual must inherit two copies of a mutated gene, one from each parent, to develop the condition. The parents, who each carry only one copy of the mutated gene, usually don't exhibit any signs or symptoms of INAD themselves.