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The treatment of genetic disorders is an ongoing battle with over 1800 gene therapy clinical trials having been completed, are ongoing, or have been approved worldwide. Despite this, most treatment options revolve around treating the symptoms of the disorders in an attempt to improve patient quality of life.
Gene therapy refers to a form of treatment where a healthy gene is introduced to a patient. This should alleviate the defect caused by a faulty gene or slow the progression of disease. A major obstacle has been the delivery of genes to the appropriate cell, tissue, and organ affected by the disorder. How does one introduce a gene into the potentially trillions of cells which carry the defective copy? This question has been the roadblock between understanding the genetic disorder and correcting the genetic disorder.
Not all genetic disorders directly result in death, however there are no known cures for genetic disorders. Many genetic disorders affect stages of development such as Down syndrome. While others result in purely physical symptoms such as muscular dystrophy. Other disorders, such as Huntington's disease show no signs until adulthood. During the active time of a genetic disorder, patients mostly rely on maintaining or slowing the degradation of quality of life and maintain patient autonomy. This includes physical therapy, pain management, and may include a selection of alternative medicine programs.
The most common X-linked recessive disorders are:
- Red-green color blindness, a very common trait in humans and frequently used to explain X-linked disorders. Between seven and ten percent of men and 0.49% to 1% of women are affected. Its commonness may be explained by its relatively benign nature. It is also known as daltonism.
- Hemophilia A, a blood clotting disorder caused by a mutation of the Factor VIII gene and leading to a deficiency of Factor VIII. It was once thought to be the "royal disease" found in the descendants of Queen Victoria. This is now known to have been Hemophilia B (see below).
- Hemophilia B, also known as Christmas Disease, a blood clotting disorder caused by a mutation of the Factor IX gene and leading to a deficiency of Factor IX. It is rarer than hemophilia A. As noted above, it was common among the descendants of Queen Victoria.
- Duchenne muscular dystrophy, which is associated with mutations in the dystrophin gene. It is characterized by rapid progression of muscle degeneration, eventually leading to loss of skeletal muscle control, respiratory failure, and death.
- Becker's muscular dystrophy, a milder form of Duchenne, which causes slowly progressive muscle weakness of the legs and pelvis.
- X-linked ichthyosis, a form of ichthyosis caused by a hereditary deficiency of the steroid sulfatase (STS) enzyme. It is fairly rare, affecting one in 2,000 to one in 6,000 males.
- X-linked agammaglobulinemia (XLA), which affects the body's ability to fight infection. XLA patients do not generate mature B cells. B cells are part of the immune system and normally manufacture antibodies (also called immunoglobulins) which defends the body from infections (the humoral response). Patients with untreated XLA are prone to develop serious and even fatal infections.
- Glucose-6-phosphate dehydrogenase deficiency, which causes nonimmune hemolytic anemia in response to a number of causes, most commonly infection or exposure to certain medications, chemicals, or foods. Commonly known as "favism", as it can be triggered by chemicals existing naturally in broad (or fava) beans.
With many different types of leukodystrophies and causes, treatment therapies vary for each type. Many studies and clinical trials are in progress to find treatment and therapies for each of the different leukodystrophies. Stem cell transplants and gene therapy appear to be the most promising in treating all leukodystrophies providing it is done as early as possible.
For hypomyelinating leukodystrophies, therapeutic research into cell-based therapies appears promising. Oligodendrocyte precursor cells and neural stem cells have been transplanted successfully and have shown to be healthy a year later. Fractional anisotropy and radial diffusivity maps showed possible myelination in the region of the transplant. Induced pluripotent stem cells, oligodendrocyte precursor cells, gene correction, and transplantation to promote the maturation, survival, and myelination of oligodendrocytes seem to be the primary routes for possible treatments.
For three types of leukodystrophies (X-linked adrenoleukodystrophy (X-ALD), metachromatic leukodystrophy (MLD) and Krabbe Disease (globoid cell leukodystrophy - GLD), gene therapy using autologous hematopoietic stem cells to transfer the disease gene with lentiviral vectors have shown to be successful and are currently being used in clinical trials for X-ALD and MLD. The progression of X-ALD has shown to be disrupted with hematopoietic stem cell gene therapy but the exact reason why demyelination stops and the amount of stem cells needed is unclear. While there is an accumulation of very long chain fatty acids in the brain, it does not seem to be the reason behind the disease as gene therapy does not correct it.
Adeno-associated vectors have also been used in intracerebral injections to treat MLD. In some patients with MLD, their IQ increased, nerve conduction improved, their MRIs appeared stable, and had normal enzyme levels. Although the greater majority of patients seem to improve after the transplant, some do not respond well to treatment, which may cause devastating outcomes. For those leukodystrophies that result from a deficiency of lysozyme enzymes, such as Krabbes disease, enzyme replacement therapy seems hopeful, however, this proves difficult as the blood-brain barrier severely limits what can pass through into the central nervous system. Due to this obstacle, most research and clinical trials are turning to allogeneic hematopoietic stem cell transplantation.
X-linked recessive inheritance is a mode of inheritance in which a mutation in a gene on the X chromosome causes the phenotype to be expressed in males (who are necessarily hemizygous for the gene mutation because they have one X and one Y chromosome) and in females who are homozygous for the gene mutation, see zygosity.
X-linked inheritance means that the gene causing the trait or the disorder is located on the X chromosome. Females have two X chromosomes, while males have one X and one Y chromosome. Carrier females who have only one copy of the mutation do not usually express the phenotype, although differences in X chromosome inactivation can lead to varying degrees of clinical expression in carrier females since some cells will express one X allele and some will express the other. The current estimate of sequenced X-linked genes is 499 and the total including vaguely defined traits is 983.
Some scholars have suggested discontinuing the terms dominant and recessive when referring to X-linked inheritance due to the multiple mechanisms that can result in the expression of X-linked traits in females, which include cell autonomous expression, skewed X-inactivation, clonal expansion, and somatic mosaicism.
Currently, no research has shown a higher prevalence of most leukodsytrophy types in any one place around the world. There is, however, a higher prevalence of the Canavan disease in the Jewish population for unknown reasons. 1 in 40 individuals of Ashkenazi Jewish descent are carriers of Canavan disease. This estimates to roughly 2.5%. Additionally, due to an autosomal recessive inheritance patterns, there is no significant difference found between affected males and affected females for most types of leukodystrophy including, but not limited to, metachromatic leukodystrophy, Krabbe disease, Canavan disease, and Alexander disease. The one exception to this is any type of leukodystrophy carried on a sex chromosome, such as X-linked adrenoleukodystrophy, which is carried on the X-chromosome. Because of the inheritance pattern of X-linked diseases, males are more often affected by this type of leukodystrophy, although female carriers are often symptomatic, though not as severely so as males. To date, there have been no found cases of a leukodystrophy carried on the Y chromosome.
Chondrodysplasia punctata is a clinically and genetically diverse group of rare diseases, first described by Erich Conradi (1882–1968), that share the features of stippled epiphyses and skeletal changes.
Types include:
- Rhizomelic chondrodysplasia punctata , ,
- X-linked recessive chondrodysplasia punctata
- Conradi-Hünermann syndrome
- Autosomal dominant chondrodysplasia punctata
X-linked myotubular myopathy (MTM) is a form of centronuclear myopathy (CNM) associated with myotubularin 1.
Genetically inherited traits and conditions are often referred to based upon whether they are located on the "sex chromosomes" (the X or Y chromosomes) versus whether they are located on "autosomal" chromosomes (chromosomes other than the X or Y). Thus, genetically inherited conditions are categorized as being sex-linked (e.g., X-linked) or autosomal. Females have two X-chromosomes, while males only have a single X chromosome, and a genetic abnormality located on the X chromosome is much more likely to cause clinical disease in a male (who lacks the possibility of having the normal gene present on any other chromosome) than in a female (who is able to compensate for the one abnormal X chromosome).
The X-linked form of MTM is the most commonly diagnosed type. Almost all cases of X-linked MTM occurs in males. Females can be "carriers" for an X-linked genetic abnormality, but usually they will not be clinically affected themselves. Two exceptions for a female with a X-linked recessive abnormality to have clinical symptoms: one is a manifesting carrier and the other is X-inactivation. A manifesting carrier usually has no noticeable problems at birth; symptoms show up later in life. In X-inactivation, the female (who would otherwise be a carrier, without any symptoms), actually presents with full-blown X-linked MTM. Thus, she congenitally presents (is born with) MTM.
Thus, although" MTM1" mutations most commonly cause problems in boys, these mutations can also cause clinical myopathy in girls, for the reasons noted above. Girls with myopathy and a muscle biopsy showing a centronuclear pattern should be tested for "MTM1" mutations.
Many clinicians and researchers use the abbreviations XL-MTM, XLMTM or X-MTM to emphasize that the genetic abnormality for myotubular myopathy (MTM) is X-linked (XL), having been identified as occurring on the X chromosome. The specific gene on the X chromosome is referred to as MTM-1. In theory, some cases of CNM may be caused by an abnormality on the X chromosome, but located at a different site from the gene "MTM1", but currently "MTM1" is the only X-linked genetic mutation site identified for myotubular or centronuclear myopathy. Clinical suspicion for X-linked inheritance would be a disease affecting multiple boys (but no girls) and a pedigree chart showing inheritance only through the maternal (mother’s) side of each generation.
Treatment can involve operations to lengthen the leg bones, which involves many visits to the hospital. Other symptoms can be treated with medicine or surgery. Most female patients with the syndrome can live a long and normal life, while males have only survived in rare cases.
Currently there is no cure for myotubular or centronuclear myopathies. Treatment often focuses on trying to maximize functional abilities and minimize medical complications, and involvement by physicians specializing in Physical Medicine and Rehabilitation, and by physical therapists and occupational therapists.
Medical management generally involves efforts to prevent pulmonary complications, since lung infections can be fatal in patients lacking the muscle strength necessary to clear secretions via coughing. Medical devices to assist with coughing help patients maintain clear airways, avoiding mucous plugs and avoiding the need for tracheostomy tubes.
Monitoring for scoliosis is also important, since weakness of the trunk muscles can lead to deviations in spinal alignment, with resultant compromise of respiratory function. Many patients with congenital myopathies may eventually require surgical treatment of scoliosis.
In May 2013, the US FDA granted Orphan drug status to Diiodothyropropionic acid (DITPA) in the treatment of MCT8 deficiency. This was following the use of DITPA towards a child in Australia, under compassionate grounds.
There is no established treatment for AHDS. Theoretical considerations suggested TRIAC (triiodothyroacetate or tiratricol, a natural non-classical thyroid hormone) to be beneficial. In 2014, a case was demonstrated in which therapy with TRIAC in early childhood led to significant improvement of cognition and mobility. Currently, the effect of Triac is under investigation.
Hypohidrotic ectodermal dysplasia (also known as "anhidrotic ectodermal dysplasia", and "Christ-Siemens-Touraine syndrome") is one of about 150 types of ectodermal dysplasia in humans. Before birth, these disorders result in the abnormal development of structures including the skin, hair, nails, teeth, and sweat glands.
X-linked recessive hypoparathyroidism is treated like other forms of the disease, using calcium and vitamin D supplementation. Supplementation with parathyroid hormone is another treatment option.
There is no cure and no standard course of treatment for Coffin–Lowry syndrome. Treatment is symptomatic and supportive, and may include occupational, physical and speech therapy and educational services.
Melnick–Needles syndrome (MNS), also known as Melnick–Needles osteodysplasty, is an extremely rare congenital disorder that affects primarily bone development. Patients with Melnick–Needles syndrome have typical faces (exophthalmos, full cheeks, micrognathia and malalignment of teeth), flaring of the metaphyses of long bones, s-like curvature of bones of legs, irregular constrictions in the ribs, and sclerosis of base of skull.
In males, the disorder is nearly always lethal in infancy. Lifespan of female patients might not be affected.
Melnick–Needles syndrome is associated with mutations in the "FLNA" gene and is inherited in an X-linked dominant manner. As with many genetic disorders, there is no known cure to MNS.
The disorder was first described by John C. Melnick and Carl F. Needles in 1966 in two multi-generational families.
X-linked recessive hypoparathyroidism is a rare, congenital form of hypoparathyroidism.
Gordon syndrome (GS), or distal arthrogryposis type 3, is a rare, autosomal dominant disorder characterized by cleft palate and congenital contractures of the hands and feet.
There does not yet exist a specific treatment for IP. Treatment can only address the individual symptoms.
Since the symptoms caused by this disease are present at birth, there is no “cure.” The best cure that scientists are researching is awareness and genetic testing to determine risk factors and increase knowledgeable family planning. Prevention is the only option at this point in time for a cure.
Usually, a common form of treatment for the condition is a type of hand cream which moisturises the hard skin. However, currently the condition is incurable.
Most cases are caused by mutations in the EDA gene, which are inherited in an X-linked recessive pattern, called x-linked hypohidrotic ectodermal dysplasia (XLHED). A condition is considered X-linked if the mutated gene that causes the disorder is located on the X chromosome, one of the two sex chromosomes. In males (who have only one X chromosome), one altered copy of the gene in each cell is sufficient to cause the condition. In females (who have two X chromosomes), a mutation must be present in both copies of the gene to cause the disorder. Males are affected by X-linked recessive disorders much more frequently than females. A striking characteristic of X-linked inheritance is that fathers cannot pass X-linked traits to their sons.
In X-linked recessive inheritance, a female with one altered copy of the gene in each cell is called a carrier. Since females operate on only one of their two X chromosomes (X inactivation) a female carrier may or may not manifest symptoms of the disease. If a female carrier is operating on her normal X she will not show symptoms. If a female is operating on her carrier X she will show symptoms.In about 70 percent of cases, carriers of hypohidrotic ectodermal dysplasia experience some features of the condition. These signs and symptoms are usually mild and include a few missing or abnormal teeth, sparse hair, and some problems with sweat gland function. Some carriers, however, have more severe features of this disorder.
Other than managing symptoms, there is currently no treatment for XLHED. However, in December 2012 Edimer Pharmaceuticals a biotechnology company based in Cambridge, MA USA, initiated a Phase I, open-label, safety and pharmacokinetic clinical study of EDI200, a drug aimed at the treatment of XLHED. During development in mice and dogs EDI200 has been shown to substitute for the altered or missing protein resulting from the EDA mutation, which causes XLHED. The initiation of a clinical study of EDI200 in neonates started in October 2013 with the first neonate tested.
The overall incidence of myotubular myopathy is 1 in 50,000 male live births. The incidence of other centronuclear myopathies is extremely rare, with there only being nineteen families identified with CNM throughout the world. The symptoms currently range from the majority who only need to walk with aids, from a stick to a walking frame, to total dependence on physical mobility aids such as wheelchairs and stand aids, but this latter variety is so rare that only two cases are known to the CNM "community".
Approximately 80% of males with a diagnosis of myotubular myopathy by muscle biopsy will have a mutation in MTM1 identifiable by genetic sequence analysis.
Many patients with myotubular myopathy die in infancy prior to receiving a formal diagnosis. When possible, muscle biopsy and genetic testing may still be helpful even after a neonatal death, since the diagnostic information can assist with family planning and genetic counseling as well as aiding in the accurate diagnosis of any relatives who might also have the same genetic abnormality.
Early journal reports of boomerang dysplasia suggested X-linked recessive inheritance, based on observation and family history. It was later discovered, however, that the disorder is actually caused by a genetic mutation fitting an autosomal dominant genetic profile.
Autosomal dominant inheritance indicates that the defective gene responsible for a disorder is located on an autosome, and only one copy of the gene is sufficient to cause the disorder, when inherited from a parent who has the disorder.
Boomerang dysplasia, although an autosomal dominant disorder, is "not" inherited because those afflicted do not live beyond infancy. They cannot pass the gene to the next generation.
Studies of the life expectancy of patients with Alport syndrome are rare, but one 2012 study of 456 male patients from across Europe who received a kidney transplant found that they had somewhat increased life expectancy compared to matched controls (the controls were "randomly selected from the same age, year, and modality categories").
There is no cure, although curative therapy with bone marrow transplantion is being investigated in clinical trials. It is believed the healthy marrow will provide the sufferer with cells from which osteoclasts will develop. If complications occur in children, patients can be treated with vitamin D. Gamma interferon has also been shown to be effective, and it can be associated to vitamin D. Erythropoetin has been used to treat any associated anemia. Corticosteroids may alleviate both the anemia and stimulate bone resorption. Fractures and osteomyelitis can be treated as usual. Treatment for osteopetrosis depends on the specific symptoms present and the severity in each person. Therefore, treatment options must be evaluated on an individual basis. Nutritional support is important to improve growth and it also enhances responsiveness to other treatment options. A calcium-deficient diet has been beneficial for some affected people.
Treatment is necessary for the infantile form:
- Vitamin D (calcitriol) appears to stimulate dormant osteoclasts, which stimulates bone resorption
- Gamma interferon can have long-term benefits. It improves white blood cell function (leading to fewer infections), decreases bone volume, and increases bone marrow volume.
- Erythropoietin can be used for anemia, and corticosteroids can be used for anemia and to stimulate bone resorption.
Bone marrow transplantation (BMT) improves some cases of severe, infantile osteopetrosis associated with bone marrow failure, and offers the best chance of longer-term survival for individuals with this type.
In pediatric (childhood) osteopetrosis, surgery is sometimes needed because of fractures. Adult osteopetrosis typically does not require treatment, but complications of the condition may require intervention. Surgery may be needed for aesthetic or functional reasons (such as multiple fractures, deformity, and loss of function), or for severe degenerative joint disease.
The long-term-outlook for people with osteopetrosis depends on the subtype and the severity of the condition in each person.The severe infantile forms of osteopetrosis are associated with shortened life expectancy, with most untreated children not surviving past their first decade. seems to have cured some infants with early-onset disease. However, the long-term prognosis after transplantation is unknown. For those with onset in childhood or adolescence, the effect of the condition depends on the specific symptoms (including how fragile the bones are and how much pain is present). Life expectancy in the adult-onset forms is normal.