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MLD-101 ... A Layperson's Overview
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MLD is short for metachromatic leukodystrophy. Translated from doctor talk MLD means: meta - change, chromatic - color, leuko - white matter, dystrophy - degeneration. MLD's name therefore comes from degeneration in the white matter of the brain and Central Nervous System (CNS) which has a color on staining that should not be there. Staining was how the disease was observed before the advent of the MRI.
Biochemistry Basically people who are affected by MLD lack an enzyme in their blood called Arylsulfatase-A, (ARSA). Without this enzyme, sulfatides are NOT broken down and instead build-up in the white matter of the brain and CNS causing destruction of the myelin sheath, or demyelination. Without an intact myelin sheath there is a breakdown in communication between the nerves and the brain. This loss of or miscommunication accounts for the loss of acquired functions, paralysis, blindness, seizures and eventual death seen in MLD.
Types of MLD Generally, there are considered to be three main types of MLD that have different ages of onset: late-infantile, juvenile, and adult. The late-infantile form of MLD is the most commonly observed form of MLD. The most common gene mutations have been identified for both the late-infantile and the adult onsets, however, there are many other less common mutations. More progression details here.
Saposin B Deficiency is a very rare form of MLD where the ARSA enzyme levels are OK, but the activator for those enzymes is missing or low. The symptoms are identical to MLD, but disease altering therapies will be different.
Those with Multiple Sulfatase Deficiency (MSD)/Austin's Disease have an activation deficiency that prevents the ARSA enzyme and many others from activating. Similar early symptoms often lead to a mis-diagnosis of MLD. You can learn more about MSD here.
MLD is not contagious and can not be passed to others through any sort of contact - it is a genetic condition.
Therapies & Research At this time there is no cure for MLD. The only treatment is bone marrow transplant (BMT) or stem cell transplant (SCT), and they are most effective in slowing the disease in people who are not showing any significant symptoms of MLD (pre-symptomatic). Research is making strides towards in the areas of improved bone marrow transplants, enzyme replacement therapy, gene therapy, and cell line studies.
Genetics MLD is an autosomal recessive genetic defect. Translated this means both males and females carry the gene and both parents need to carry the defective gene in order to have an affected child. It is estimated the carrier defect occurs in in the general population at 1 in every 100 people and the affected birth rate is 1:40,000 – thus MLD gets its designation of being a rare disease.
Our experience, however, is the most frequent form of MLD, infantile onset, is often not diagnosed properly prior to death of the patient and later onsets of MLD are often misdiagnosed as ADHD, ADD, or psychiatric conditions and hence the frequency might be higher than reported.
Incidence and Prevalence We estimate that approximately 2,000 new late infantile babies are born each year (60 in the US and 100 in Europe) and there are approximately 49,000 people alive at any given time with all forms of MLD worldwide. We have a video with more details tables you can view here.(Source: MLD Foundation 2017-01)