Metachromatic leukodystrophy (MLD) is a rare disorder that allows lipids to build up in certain cells of the body. The cells around the spinal cord, brain, and peripheral nerves are the most affected by this inherited condition.
This genetic disorder is caused by a deficiency in a certain enzyme that helps to break down these fatty substances, preventing them from building up and causing cell damage in the body.
There are three forms of this disease, and each affects different age groups. The age ranges are late infantile form, juvenile, and adult form.
MLD causes damage to the protective covering of the nerves known as myelin. Symptoms associated with a deterioration in both brain and nervous system function are experienced in those with these different forms of MLD.
Symptoms include loss of intellect and memory due to damage caused to the cells in the brain. Nerve cell damage often leads to the inability to sense touch and pain due to loss of nerve sensation and numbness.
Progressive nerve damage can also cause a loss of motor skills, making walking, speaking, talking, and swallowing difficult. A loss of balance, along with stiff muscles and painful muscle spasms, can also lead to episodes of paralysis.
Sight can be affected if the optic nerve is damaged, and loss of bladder and bowel control can also be experienced. Even hearing can be affected by this condition.
Seizures are possible, and so are episodes of depression and emotional distress. Behavioural problems can also follow.
The late infantile form is the most common form of MLD, and symptoms can begin to show at around two years of age. Loss of muscle function can be rapid, meaning that children with late infantile MLD do not live long.
The juvenile form is the second most common, and symptoms strike between the ages of three and 16 years of age. Cognitive impairment, along with behaviour problems, are the first symptoms to show. Progression of the disease is slower than in the late infantile form, but life expectancy beyond 20 years of the onset of symptoms is rare.
The adult form of MLD is less common than the other two, and as the name suggests, symptoms do not develop until adulthood. Poor performance at school or college can be an early indicator that symptoms have begun. Alcohol and drug abuse are also common. However, life expectancy is much longer for those with the adult form, as periods where symptoms stabilise are experienced.
A deficiency in the enzyme that helps to break down lipids called sulfatides is the cause of MLD. These fats build up in cells and cause them to malfunction. This inability to break down these fats also leads to the protective layer around nerve cells, known as myelin, becoming damaged.
Risk factors include both parents being carriers of the mutated gene responsible for causing MLD. One mutated gene from each parent is needed to cause this illness. The most common cause of MLD is a mutation in the ARSA gene.
A physical and neurological examination is usually performed to diagnose this condition. Blood tests for enzyme deficiency and a urine test to check sulfatide levels are also usually performed. Genetic testing can also help to confirm the presence of the mutated genes.
MLD cannot be cured, so the focus of treatments is on delaying the progression of the disorder. This can be done by mixing medications, physical therapy, and nutritional assistance together to help lessen the impact of the numerous symptoms this condition produces.
Preventing MLD can only be achieved through testing potential parents for the gene mutation which causes this disorder. Then, potential parents can choose if they want to risk starting a family if the mutation is present in both adults.