Definition:
Late onset variant CLN6 disorder is part of a group of progressive degenerative neurometabolic disorders known as neuronal ceroid lipofuscinoses (NCLs).  NCLs are characterized by an abnormal accumulation of lipopigaments, which are substances combined of fats and proteins within the brain’s nerve cells, eyes, skin, muscle, and within other tissues throughout the body.

The mutated gene in variant late infantile NCL was recently cloned.  This breakthrough allows for carrier testing, for accurate diagnosis, and fuels promise for a future cure.  Late onset variant CLN6 disorder is caused by a mutation on the CLN6 gene, which leads to an accumulation of transmembrane proteins in the cells. The gene CLN6 provides the code for a protein known as linclin.  Linclin plays an important role in the function of cellular membranes and in providing energy to nerve cells.  This mutation essentially eliminates the function of the CLN6 gene and gives rise symptoms of this disorder.  More than 18 mutations on the CLN6 gene have been identified. This disorder causes nerve cells, found in the brain, retina, and in the central nervous system, to die.

Late onset variant CLN6 predominately affects those of Indian ancestry as well as descendants of Spanish settlers in Costa Rica, although the exact prevalence among those groups are not known.  It is estimated that the NCLs affect two to four of every 100,000 live births in the United States.

Symptoms:
Symptoms of Late onset variant CLN6 begin between five to seven years of age.  Seizures and a loss of motor skills appear first.  Blindness occurs after initial symptoms appear.  As the disorder progresses, cognition declines and the affected individual becomes increasingly incapacitated.

Inheritance Pattern:
Early juvenile CLN6 is an autosomal recessive disorder.

Life Expectancy:
Life Expectancy for Late onset variant CLN6 is during the mid 20s.

Diagnosis and Testing:
A DNA analysis may be utilized to confirm a mutation on the CLN6 gene and a diagnosis of Late onset variant CLN6.  For this test, blood or a tissue sample is analyzed from individuals suspected of having the disorder or from members of families wherein a carrier of the CLN6 gene has been identified.  Prenatal screening is also available.

Treatment:
There is no cure for Late onset variant CLN6.  Treatment is limited to reducing or controlling the symptoms of this disorder.  Neurologists can assist in controlling seizures or nervous system complications.  An ophthalmologist can monitor vision loss, and physical and occupational therapists can help the affected individual maintain muscle movement and reduce muscle discomfort.