1. Overview of LHON: Molecular Genetics, Risk Factors for Visual Loss, Visual Prognosis
Patrick Yu-Wai-Man, BMedSci, MBBS, PhD, FRCPath, FRCOphth: Hi, there. My name is Patrick Yu-Wai Man. I am an academic neuro-ophthalmologist based at the University of Cambridge with joint clinical appointments at Addenbrooke’s Hospital in Cambridge and Moorfields Eye Hospital in London. I would like to welcome you to this educational program, “Neuro-Ophthalmology: What You Need to Know About LHON.” This program consists of a series of 33 expert commentaries. I will start with an overview of Leber hereditary optic neuropathy (LHON). I will go over the molecular genetics of LHON, the risk factors of visual loss, and the visual prognosis. Professor Valerio Carelli will then discuss the clinical features and the diagnosis of LHON. Finally, Professor Nancy Newman will review current and emerging treatments for this mitochondrial optic neuropathy.
Let us start with some historical perspective. LHON was originally described by Albrecht Von Graefe in 1858. It was then formally defined by Theodor Leber in his seminal monograph in 1871. We then had to wait until 1988 before the molecular genetic basis of LHON was finally established. LHON is a fairly rare disease. The reported prevalence figures range from 1 in 31,000 in the United Kingdom to 1 in 39,000 in Denmark, and 1 in 50,000 in Finland. There is no accurate data on the annual incidence of LHON. Estimates of 1 new case of LHON per 2 to 3 million have been put forward.
LHON is a primary mitochondrial genetic disorder and 3 point mutations within the mitochondrial genome account for about 90% of all cases. These are located at positions 3460, 11778, and 14484, with 11778 being the most common pathogenic LHON mutation worldwide. The 11778 mutation accounts for 60% to 70% of cases in Europe and in North America, and for about 90% of cases in Asia. If you have a strong clinical suspicion of LHON and the patient is negative for the 3 common mutations, the next step is whole mitochondrial genome sequencing. There is a long list of these rarer LHON mutations, and you can read more about them. An important message for patients and their families is that the mitochondrial genome shows strict maternal inheritance. A man will not transmit his mitochondrial DNA (mtDNA) mutation to his own children.
The 3 common mtDNA mutations all affect key sub-units of Complex I of the mitochondrial respiratory chain. These mutations lead to a decrease in ATP production and to increased levels of reactive oxygen species, which are pretty nasty stuff for a cell. There is selective involvement of retinal ganglion cells resulting in optic nerve degeneration and visual loss. The retinal ganglion cells within the papillomacular bundle are affected early and much more severely, accounting for the dense central scotoma. In the majority of patients with LHON, the disease is monosymptomatic, limited to the optic nerve. A small subgroup of LHON carriers will develop a more severe phenotype known as LHON-plus, where the visual loss is complicated by additional neurological features. The 3 strongest causal associations are with dystonia, myoclonus, and in multiple sclerosis(MS)-like illness that is frequently referred to as Harding’s disease.
So, who gets the disease and when? The peak age of onset is between the ages of 15 and 35. However, you should also keep in mind that about 10% of carriers will become affected before the age of 12, and visual loss can occur at any time with the oldest reported case in an 87-year-old man. LHON is characterized by marked sex bias. About 50% of male carriers will lose vision compared with about 10% of female carriers during their lifetime. A male carrier is therefore about 5 times more likely to be affected than a female carrier, and over 80% of LHON patients are men.
As not all LHON carriers will lose vision, what are the risk factors for visual loss in this mitochondrial disorder? The 2 main risk factors are sex and age. For example, a 25-year-old male carrier has a much higher risk of losing vision compared with a 60-year-old female carrier. There is evidence that estrogens are neuroprotective, accounting for the lower penetrance among female carriers.
The role of environmental risk factors has also been studied in LHON. Smoking is a major risk factor for visual loss. In 1 study, heavy smokers were over 3 times more likely to be affected than nonsmokers. A trend was observed with excessive alcohol consumption, but this association was not as strong. The current thinking is that LHON is a complex disease with several factors — genetic, environmental, and hormonal — contributing to visual loss in this mitochondrial disorder. So what is the visual prognosis in LHON? LHON causes severe bilateral visual loss with poor visual recovery. In a recently published meta-analysis of 12 retrospective and 3 prospective studies involving 695 patients, visual recovery, which was variably defined, was reported in 14.4% of patients, with all ages included. The 14484 mutation carries a better visual prognosis compared with the 3460 and 11778 mutations. Children who lose vision at the age of 12 years or younger also tend to do better in terms of their final visual outcome.
It is therefore not surprising that LHON has a major impact on quality of life. Patients can find it very hard not being able to recognize people’s faces and expression. There is also a loss of independence that comes from not being able to drive anymore, and for some patients, the financial impact of job loss can be quite distressing. LHON is associated with significant psychological morbidity with high rates of anxiety and depression.
These are my take-home messages. LHON is a disease of young adult men. Three mtDNA mutations account for most cases of LHON, and they are known by their numbers, 3460, 11778, and 14484. The visual prognosis unfortunately is poor, with limited visual recovery for most affected patients.
Thank you for watching. Please continue to the next presentation.
2. Detection and Diagnosis of LHON
Valerio Carelli, MD, PhD: Hello. I’m Dr Valerio Carelli, I direct the Laboratory of Neurogenetics at the Department of Biomedical and Neuromotor Sciences here at the University of Bologna in Italy. Today I will talk about how we can recognize and diagnose LHON.
As you already heard from Patrick-Yu-Wei-Man before, LHON is a rare disorder. The prevalence, depending on which studies and countries have been considering it, may range between 1 in 30,000 and 1 in 50,000 people. For this reason, doctors, neurologists, but also ophthalmologists, on average, may not be very aware of this entity — and so not very familiar with the clinical manifestations of the disease. This usually leads to an important delay in the correct diagnosis of the patient, which is important for establishing, as early as possible, a therapy.
The disease is insidious. It’s usually a painless and quite rapid progressive loss of central vision. This usually affects 1 eye, and it is followed by the fellow eye in days, weeks, or months. Most people become bilateral within a year. The truly monolateral cases are extremely rare. In a subset of people, the loss of vision can be bilateral from the onset.
The diagnosis of LHON must be considered by doctors in the first place as a clinical diagnosis. This is based on some quite peculiar features that we must learn to recognize in order to suspect the disease. One very indicative and important piece of information that must be gathered from the analysis of the patient is the possibility that along the maternal line, other people have been affected by an unexplained visual loss. This is a strong indication of maternal inheritance and we need to think of Leber’s in that case.
The disease itself is divided into 4 stages. This was agreed in a consensus conference that we held recently, and it was published. Essentially, most people may stay without symptoms forever, and so there is a sort of asymptomatic stage. People carrying the mutation do not necessarily develop the disease. However, a subset of these people can have a transition from the asymptomatic stage to a symptomatic stage.
At this point, we distinguish a subacute phase, which is usually within 6 months of onset. And you have the rapid decrease of visual function in this first 6 months. The second 6 months is called the dynamic phase. At this point, visual acuity (VA) is already very much reduced. But many of the results, like the optical coherence tomography (OCT) exams, are still dynamically evolving and changing over time. Usually after 1 year, the disease is completed and you enter the chronic phase. So after 12 months, the parameters are not changing anymore.
There are some exceptions to this paradigm. You may have, in some cases, a slowly progressive evolution of the disease, which may pose some problems for differential diagnosis. Usually the disease starts at a young adult age. But in a subset of people, the disease starts in childhood, under 12 years of age. It’s possible also that you have onset at a late stage, after 44 years of age. Essentially, you must be alert to the possibility of LHON at any age.
The key investigations and the clinical features that must be recognized are loss of VA, particularly central vision; this is well recognized by visual field perimetry. Loss of color vision is also a very early event. From those examinations, you can recognize some quite specific signs, like swelling of the fibers, initial pallor on the temporal sector of the optic nerve head, and changes in the vasculature: so a microangiopathy, which is quite characteristic of LHON. Obviously, these are qualitative evaluations of fundus that can be quantified by the OCT exam. The fundus exam and the OCT should be perfectly congruent, and VA is congruent with the appearance of the central scotoma at visual field perimetry.
In order to confirm the clinical suspicion of LHON, you must certify the diagnosis by genetic testing. And from that point of view, the family history is extremely important because, as I said at the beginning, maternal inheritance is a very strong indication of LHON, as only mtDNA defects are maternally inherited. So this is very important information.
There is a large subset of patients that are sporadic, however. So you cannot recognize any inheritance. Or maybe you have siblings who are affected in the same generation. And we now are aware that there are very rare forms, which are recessively inherited.
So if you have maternal inheritance, the first genetic testing is to request a search for the 3 very common mtDNA mutations, which cover 90% of the cases. If you are not positive for the 3 mutations, but you still have maternal inheritance in the family, then specialized centers should run the complete mtDNA sequencing analysis. If mtDNA is not affected by any variant which can be considered as pathogenic, at that point, you have to consider running exome sequencing for searching recessive mutations in nuclear genes.
From the differential diagnosis point of view, obviously the very first diagnosis that, on average, a neurologist and ophthalmologist thinks of is an inflammatory form, so an optic neuritis. But you may also have toxic and metabolic forms of optic nerve atrophy, as well as compressive optic neuropathies. Obviously, you have to think of maculopathies. Ultimately you can also think of non-organic visual loss. In some very rare occurrences, Leber’s is syndromic, so it is linked to other neurological symptoms. And in particular, you can have symptoms which are quite similar to what you would see in MS. And there is a variant where the 2 disturbances are coincidentally the same in the same patient.
In the end, it would be very good if when the neurologist and the ophthalmologist have a suspicion of LHON, they then refer the patients to specialized centers where the diagnostic algorithm is completed. In particular, the rapidity for the genetic testing is a key issue because the delay in diagnosing LHON can be quite important in terms of establishing a correct therapies from the beginning.
Obviously, to follow up the patient properly over time, you need to collect some key exams. And VA and visual field testing are the 2 instrumental exams that are subjectively dependent on the patients and are the most important. But they also give you an objective anatomical measure with specific quantification of the defect, as these may evolve over time with loss of fibers, swelling, and then loss of fibers, and ultimately atrophy.
There are a few key things to remember. You have to look at the maternal inheritance. This is an extremely important message. You have to think of LHON if the symptoms are in a young adult male, and if the loss of vision is characterized by central scotoma without pain and without inflammation. The ultimate diagnosis comes from the molecular diagnostics, and this is a test that should be done as quickly as possible. These are the key features. Thank you for watching, and please remain for the next presentation.
3. Current and Emerging Treatments for LHON
Nancy J. Newman, MD: Hello, I’m Nancy Newman and I’m professor of ophthalmology and neurology at the Emory University School of Medicine in Atlanta, Georgia, United States. I would like to talk about current and emerging treatments for LHON, including disease modifying agents, gene therapy, and symptomatic treatments.
But first treatment actually begins in your office once the diagnosis is confirmed with genetic counseling for LHON. It is your job to inform the patient of the risk of LHON inheritance and visual loss in their children and relatives. Remember, although male patients have a higher risk of vision loss than their female relatives, they cannot pass on the disease to their children. On the other hand, all females in the maternal lineage, whether affected or not, will pass on the risk of the disease to all their children.
Now LHON is actually an ideal laboratory for testing treatment efficacy. First of all, there are well studied natural history studies, which show the generally poor prognosis of this disease. The disease has a sudden onset, which allows for precision in treatment timing. There is sequential vision loss recognized in at least 50% of patients, which allows for a therapeutic window in which you might be able to stop the second eye from being involved. Finally, the target of this disease, the retinal ganglion cells, is quite accessible via topical therapy to the eye or intravitreal therapy.
The treatments for LHON so far are mostly disease modifying treatments. These include primarily your antioxidants and your so-called mitochondrial cocktails. Among them the most well-known is coenzyme Q10 (CoQ10), but it has had no definite success in the treatment of Leber’s. A similar compound, idebenone, however, stimulates ATP production by bypassing Complex I of the mitochondrial respiratory chain, somewhat like CoQ10, but it is a much more potent antioxidant, it has an excellent safety profile and it is indeed the first treatment approved for the treatment of Leber’s, but only in the European Union. This occurred in 2015.
This was based initially on 2 studies reported in Brain in 2011. One was a retrospective study out of Italy, which looked at patients with Leber’s vision loss within 1 year of onset and did not randomly treat patients with idebenone, but those that were treated seemed to show an increased frequency of improvement, especially if they had the 11778 mutation. This improvement seemed to be related to earlier treatment.
In the first randomized controlled trial for the treatment of LHON, RHODOS, patients within 5 years of the onset of vision loss from Leber’s were randomized to treatment with idebenone or not. This involved all 3 primary mutations. There was a trend for better VA at 6 months, although it did not meet its primary endpoint. There seemed to be more improvement among those patients earlier in the course of their disease.
This prompted an International Consensus Statement on Leber’s that was published in the Journal of Neuro-Ophthalmology in 2017, to say that in subacute or dynamic patients, treatment with idebenone at 900 mg per day should be continued for at least 1 year to assess the start of therapeutic response or until a plateau in terms of improvement is reached. Further studies via an expanded access program for idebenone has suggested that treatment duration of longer than 1 year, perhaps at least 2 years, is needed to maximize the probability of observing an effect with idebenone.
Other proposed therapies have included other antioxidant and mitochondrial cocktails with nutritional supplements, anti-apoptotic drugs, photobiomodulation, agents that promote mitobiogenesis, neuroprotection, and stem cell therapy. All are either still in animal model stages or have yet to show efficacy in human Leber’s studies.
Let’s move on to gene therapy, which I think is the most exciting new findings in this disorder. We have challenges with gene therapy in all disorders, but particularly with mtDNA disorders. There are several types of techniques that are being used. But the 2 I want to talk about today are nuclear transfer techniques and allotopic rescue.
Nuclear transfer techniques, or so-called mitochondrial replacement therapy, is where the nucleus of a carrier female with a mtDNA mutation, is then placed in an enucleated donor cytoplasm with donor mitochondria and therefore donor mtDNA. That egg is then put with the sperm in vitro fertilization and reimplanted. You then get a child that has the nuclear DNA of both parents, but the mitochondria and the mtDNA of the donor. This essentially cures the disease in the germline. We know of at least 1 healthy child reported in the newspapers that is the result of this technology. This technology has been approved in the UK under exceptional circumstances, but I’m unaware if it is being performed systematically anywhere else.
What about direct gene therapy for those patients already with Leber’s or carriers of Leber’s? Well, we have a lot of experience with inserting DNA into the nucleus of cells. However, it is challenging and not yet established that we can get DNA directly into mitochondria and into mtDNA. So what can we do with that? We can do something called allotopic rescue, which takes advantage of the fact that although mtDNA is absolutely necessary within the mitochondria to code for proteins necessary for mitochondrial function, the reality is that 90% of the proteins necessary for mitochondrial function are actually coded for on nuclear genes made in the cytoplasm on the endoplasmic reticulum. These proteins are then transported into the mitochondria.
With allotopic rescue we therefore can get a copy of a mitochondrial piece of DNA, into the nuclear genome, have that protein made in the cytoplasm and then have a targeting sequence on it, which allows that protein to know it needs to be transported into the mitochondria. All allotopic rescue gene therapy trials to date have been on patients with the 11778 mutation of Leber’s, the most common and the most severe.
Allotopic rescue has shown proof of principle in animal models and has been shown to be safe in human models. Gene therapy trials with this technology are ongoing in Europe, the United States, and in China. In 2 pivotal studies using this technology, RESCUE and REVERSE, LHON patients with vision loss, within 1 year (for RESCUE it’s within 6 months; with REVERSE it’s from 6 months to 12 months). Each patient has 1 of their 2 eyes randomly assigned to a single intravitreal injection of the gene therapy and the other eye received sham therapy.
The process was well tolerated with a fair amount of intraocular inflammation, but it was responsive to conventional treatment and without sequelae. The results of these 2 trials have now been published in the literature and have shown that there appears to be a favorable effect. Patients gain about 27 Early Treatment Diabetic Retinopathy Study (ETDRS) letters from nadir and 71% of RESCUE and 76% of REVERSE patients had at least a -0.3 logMAR gain from nadir in at least 1 eye. 71% of RESCUE and 81% of REVERSE patients had a clinically relevant recovery, which is approximately 10 letters from nadir in at least 1 eye. And this was sustained over 3 years.
What was surprising is that this improvement was in both the treated eyes and the sham eyes. This raised the question of whether we were just simply seeing the natural history of the disease and that we had not got it right in the past. To look into this, we recently did a meta-analysis, looking at all the natural history patients in the literature for which we had VA data and compared them to the eyes of all the patients in RESCUE and REVERSE.
Indeed, the RESCUE and REVERSE eyes did at least -0.33 logMAR better than the natural history patients. So, what is allowing for this bilateral effect? Subsequent studies on monkeys have shown that when you inject the gene therapy into 1 eye, that 3 months later, you can find evidence of that gene therapy in the opposite optic nerve and the opposite retina. Suggesting that there may be transfer across the chiasm.
Finally, I cannot help but mention symptomatic treatment because it is of utmost importance in these patients. These patients have a terrible effect on their quality of life (QoL) and they need to be helped. You can do this by referring them, or yourself improving their QoL with low vision aids, helping them to read, navigate, communicate, be employed and even drive. They also should be advised to avoid mitochondrial toxicity, as should all carriers of this disease by avoiding tobacco use, heavy alcohol use, and medications with mitochondrial toxicity.
Support groups and patient organizations have transformed this disease and other rare diseases. Social media growth makes it easier for LHON patients and their families to connect for education and support and has made recruitment for these clinical trials much easier with just a click of a mouse.
In conclusion, be knowledgeable about maternal inheritance. Consider recommending idebenone, especially if you are within the European Union and your patients are within the first year of Leber’s visual loss. Consider maintaining the idebenone more than 1 year if your patient is responding. Stay tuned for gene therapy options as they hopefully become approved. Don’t forget symptomatic treatments and low vision referral. Direct your patients to patient organizations for support, education, and potentially clinical trial enrollment.