The inheritance probabilities per birth are as follows:
If both parents are carriers:
25% (1 in 4) children will have the disease
50% (2 in 4) children will be carriers, but unaffected
25% (1 in 4) children will be free of MLD – unaffected child that is not a carrier
If one parent is affected and one is free of MLD:
0% (0) children will have the disorder – only one parent is affected, other parent always gives normal gene
100% (4 in 4) children will be carriers (but unaffected)
If one parent is a carrier and the other is free of MLD:
50% (2 in 4) children will be carriers (but unaffected)
50% (2 in 4) children will be free of MLD – unaffected child that is not a carrierIn addition to these frequencies there is a pseudo-deficiency that affects 7–15% of the population. People with the pseudo deficiency do not have any MLD problems unless they also have affected status. With the current diagnostic tests, Pseudo-deficiency reports as low enzyme levels but sulfatide is processed normally so MLD symptoms do not exist. This phenomenon wreaks havoc with traditional approaches to Newborn Screening so new screening methods are being developed. Diagnosis
Clinical examination and MRI are often the first steps in an MLD diagnosis. MRI can be indicative of MLD but is not adequate as a confirming test. An ARSA-A enzyme level blood test with a confirming urinary sulfatide test is the best biochemical test for MLD. The confirming urinary sulfatide is important to distinguish between MLD and pseudo-MLD blood results.
One of the patients had characteristic KSS, while the other patient had a very different disease known as Pearson marrow pancreas syndrome. Complicating the matter, in some cases Pearsons syndrome has been shown to progress into KSS later in life.More recent studies have concluded that mtDNA duplications may also play a significant role in determining what phenotype is present. Duplications of mtDNA seem to be characteristic of all cases of KSS and Pearsons syndrome, while they are absent in CPEO.Deletions of mtDNA in KSS vary in size (1.3–8kb), as well as position in the mitochondrial genome. The most common deletion is 4.9kb and spans from position 8469 to position 13147 on the genome. This deletion is present in approximately ⅓ of people with KSS

Diagnosis
A neuro-ophthalmologist is usually involved in the diagnosis and management of KSS. An individual should be suspected of having KSS based upon clinical exam findings. Suspicion for myopathies should be increased in patients whose ophthalmoplegia does not match a particular set of cranial nerve palsies (oculomotor nerve palsy, fourth nerve palsy, sixth nerve palsy). Initially, imaging studies are often performed to rule out more common pathologies. Diagnosis may be confirmed with muscle biopsy, and may be supplemented with PCR determination of mtDNA mutations. Biopsy findings
It is not necessary to biopsy an ocular muscle to demonstrate histopathologic abnormalities. Cross-section of muscle fibers stained with Gömöri trichrome stain is viewed using light microscopy. In muscle fibers containing high ratios of the mutated mitochondria, there is a higher concentration of mitochondria.