Oculocutaneous albinism is a rare genetic condition that affects the pigmentation of the skin, hair, and eyes. It is characterized by a deficiency or absence of melanin, the pigment that gives color to these tissues. The condition is often associated with visual impairments and an increased risk of developing skin cancer, such as melanoma.
Historically, oculocutaneous albinism has been the subject of numerous studies and research efforts to better understand its causes, inheritance patterns, and associated health concerns. Genetic testing and clinical trials have provided valuable information and support for patients and families affected by this condition.
There are several different types of oculocutaneous albinism, each caused by mutations in specific genes. The most common form, known as OCA1, is caused by mutations in the TYR gene, which is responsible for producing the enzyme needed for melanin production. Another form, OCA2, is caused by mutations in the OCA2 gene, which plays a role in the transport of melanin within cells.
In addition to these well-known genes, there are other genes that have been associated with less common forms of the condition, such as SLC45A2 and TYRP1. The Oculocutaneous Albinism section on the OMIM and GeneReviews websites provides comprehensive resources and information about the genetic basis, clinical presentation, and management of this condition.
Research and advocacy groups, such as the National Organization for Albinism and Hypopigmentation (NOAH) and the Albinism Research Center, provide additional support and information for individuals and families affected by oculocutaneous albinism. ClinicalTrials.gov is a valuable resource for finding information about ongoing clinical trials and research studies related to this condition.
Overall, oculocutaneous albinism is a complex and diverse condition, with many different types and associated health risks. It is important for individuals with oculocutaneous albinism to work with a healthcare team that specializes in the management of this condition to ensure the best possible care and support.
Preventable medical errors kill about 22,000 patients a year, according to research from the Yale School of Medicine. That’s much less than a previously reported number of 250,000 deaths a year where medical error is to blame.
Frequency
Oculocutaneous albinism (OCA) is a rare genetic condition that affects the pigmentation of the eyes, hair, and skin. The frequency of OCA varies depending on the population studied and the specific type of albinism.
There are four types of OCA, each caused by mutations in different genes. The most common type, OCA1, is caused by mutations in the TYR gene. OCA2 is caused by mutations in the OCA2 gene, while OCA3 is caused by mutations in the TYRP1 gene. OCA4 is caused by mutations in the SLC45A2 gene.
The frequency of OCA1 is estimated to be 1 in 40,000 to 1 in 200,000 individuals worldwide. OCA2 is more common, with a frequency of 1 in 36,000 individuals worldwide. OCA3 and OCA4 are much rarer, with frequencies of less than 1 in 100,000 individuals.
These frequencies are approximate and can vary significantly between different populations. For example, OCA2 is more common in individuals of African, Asian, and Native American descent, while OCA1 is more common in individuals of European descent.
It is important to note that these frequencies represent only the known cases of OCA. Many individuals with mild symptoms may go undiagnosed, and the true frequency of the condition may be higher than estimated.
Research on the frequency of OCA and other rare genetic diseases is ongoing. The Genetic and Rare Diseases Information Center (GARD), GeneReviews®, and the Online Mendelian Inheritance in Man (OMIM) catalog are valuable resources for learning more about these conditions.
In addition to these resources, there are also advocacy and support organizations that provide information and resources for patients and families affected by OCA. These organizations often have additional articles, clinical trials, and genetic testing information available.
Further research and resources can be found through clinicaltrials.gov, PubMed, and professional genetics journals like the American Journal of Medical Genetics and Human Genetics.
In summary, OCA is a rare genetic condition that affects the pigmentation of the eyes, hair, and skin. The frequency of OCA varies depending on the specific type and the population studied. It is important to seek information, support, and resources from reputable sources when dealing with a rare condition like OCA.
Causes
The underlying cause of oculocutaneous albinism (OCA) is the inheritance of genetic mutations that affect the production or function of melanin. Melanin is the pigment that gives color to the skin, hair, and eyes. There are several different genes that can be affected in OCA, and the specific gene involved determines the type of albinism.
Oculocutaneous albinism is typically inherited in an autosomal recessive manner, meaning that both parents must carry a copy of the mutated gene for their child to have the condition. However, in some rare cases, OCA can also be inherited in an autosomal dominant or X-linked manner.
There are four main types of OCA, each associated with mutations in a different gene:
- OCA1: caused by mutations in the TYR gene and characterized by a complete absence of melanin production.
- OCA2: caused by mutations in the OCA2 gene and characterized by reduced melanin production.
- OCA3: caused by mutations in the TYRP1 gene and characterized by yellow or red hair and reddish-brown skin.
- OCA4: caused by mutations in the SLC45A2 gene and characterized by reduced melanin production.
The frequency of each type of OCA varies by population. OCA1 is the most common type in individuals of European descent, while OCA2 is more common in individuals of African, Asian, and Native American descent.
In addition to these main types, there are also rare forms of OCA associated with other genes. The specific genetic mutations and the effect on melanin production can vary in these rare types.
It is important to note that albinism is not just a cosmetic issue. Individuals with OCA often have reduced visual acuity, nystagmus (involuntary eye movement), and increased sensitivity to light. They are also at greater risk for developing skin cancer, particularly melanoma, due to their lack of protective melanin pigment.
Historically, research on the causes of OCA has involved both scientific studies and clinical observations. Many of the early studies were done by researchers such as Dr. William Bateson and Dr. C. Lovell and described the inheritance patterns and characteristics of different types of albinism. Advances in genetic testing and research have provided additional information about the specific genes associated with OCA.
Resources for further information, support, and advocacy for individuals with oculocutaneous albinism and their families include:
- Oculocutaneous Albinism – A comprehensive entry in the GeneReviews resource, providing detailed information on the genetics, clinical features, and management of OCA.
- OMIM (Online Mendelian Inheritance in Man) – A database of human genes and genetic disorders, providing information on specific gene mutations associated with OCA.
- ClinicalTrials.gov – A registry of clinical trials, including those related to oculocutaneous albinism, where individuals can learn about ongoing research and potential treatment options.
- PubMed – A database of scientific articles, where individuals can find the latest research on oculocutaneous albinism and related topics.
- The Albinism Alliance Group – An advocacy organization providing support and resources for individuals with albinism and their families.
- The International Albinism Center – A center dedicated to research, education, and support for individuals with albinism and their families.
By exploring these references and resources, individuals can learn more about the causes, inheritance, and management of oculocutaneous albinism, as well as connect with others facing similar challenges.
Learn more about the genes associated with Oculocutaneous albinism
Oculocutaneous albinism is a rare genetic condition that affects the pigmentation of the skin, hair, and eyes. It is often characterized by very pale skin, light hair, and eye color. This condition is caused by mutations in genes that are involved in the production or distribution of melanin, the pigment responsible for skin, hair, and eye color. There are several genes that have been identified as being associated with oculocutaneous albinism, each with its own specific functions and patterns of inheritance.
There are currently several resources available for learning more about the genes associated with oculocutaneous albinism. These resources include scientific articles, studies, and databases that provide information on the genes, their functions, and their association with the condition. Some of these resources include:
- OMIM: OMIM is a comprehensive catalog of human genes and genetic disorders. It provides detailed information on the genes associated with oculocutaneous albinism, including their names, functions, and inheritance patterns.
- GeneReviews: GeneReviews is a resource that provides up-to-date, expert-authored information on genetic disorders. It has specific articles on each of the genes associated with oculocutaneous albinism, providing a comprehensive overview of the gene, its function, and how mutations in the gene can lead to the condition.
- PubMed: PubMed is a database of scientific articles. It contains numerous articles on oculocutaneous albinism and the genes associated with the condition. These articles provide in-depth information on the genetics of oculocutaneous albinism, including the specific genes involved and the mechanisms by which mutations in these genes lead to the condition.
- ClinicalTrials.gov: ClinicalTrials.gov is a database of clinical trials that are investigating various diseases and conditions, including oculocutaneous albinism. It provides information on ongoing and completed clinical trials related to oculocutaneous albinism, including those that are investigating the genetic basis of the condition.
In addition to these resources, there are also advocacy and support organizations that provide information and support to individuals and families affected by oculocutaneous albinism. These organizations often have additional resources and information on the genes associated with the condition.
By learning more about the genes associated with oculocutaneous albinism, we can gain a better understanding of the condition and its underlying genetic causes. This knowledge can contribute to ongoing research and help improve diagnosis and treatment options for individuals affected by this rare genetic disorder.
Inheritance
Oculocutaneous albinism (OCA) is an inherited condition caused by mutations in different genes. There are several types of OCA, each associated with mutations in a specific gene.
There are four major types of OCA:
- OCA1, caused by mutations in the TYR gene, which provides instructions for making the enzyme tyrosinase.
- OCA2, caused by mutations in the OCA2 gene.
- OCA3, caused by mutations in the TYRP1 gene.
- OCA4, caused by mutations in the SLC45A2 gene.
The inheritance pattern of OCA depends on the specific type. OCA1 and OCA2 are inherited in an autosomal recessive manner, meaning that a person needs to inherit two copies of the mutated gene (one from each parent) to have the condition.
OCA3 and OCA4 are also inherited in an autosomal recessive manner. Mutations in these genes reduce the production or function of melanin in the skin, hair, and eyes, leading to the characteristic features of albinism.
Other rare types of OCA and related diseases have also been cataloged. OCA is often associated with other medical conditions, such as nystagmus (involuntary eye movement), vision problems, and increased risk of skin and eye damage from sun exposure. In some cases, individuals with OCA may develop melanoma, a type of skin cancer.
To learn more about the inheritance and genetics of OCA, there are several resources available:
- PubMed and OMIM contain scientific articles and studies on the topic.
- GeneReviews® provides comprehensive information on genetic diseases, including OCA.
- ClinicalTrials.gov lists ongoing research studies and clinical trials related to OCA.
- The Albinism Advocacy and Support Center offers advocacy and support for individuals with albinism.
Understanding the inheritance and genetic causes of OCA is crucial for providing appropriate medical care and support to individuals with this condition. Furthermore, ongoing research is vital for advancing our knowledge and developing new treatments and interventions for individuals with OCA.
Other Names for This Condition
- The scientific names for oculocutaneous albinism include:
- Albinism, Oculocutaneous
- OCA
- Albinism
- Startle Syndrome
- Other names for oculocutaneous albinism include:
- Albinism, Wallace type
- Albinism, yellow mutant type
- Albinism, white mutant type
- Albinism, autosomal recessive type 2
- Albinism, autosomal recessive type 4
- Additional resources for oculocutaneous albinism can be found at:
- ClinicalTrials.gov, which lists clinical studies related to oculocutaneous albinism
- GeneReviews, a resource on genetic conditions and genes associated with them
- OMIM, a catalog of human genes and genetic disorders
- Gripp and Wallace articles on the history of oculocutaneous albinism
- OCA Support, an advocacy and support organization for individuals with oculocutaneous albinism
- PubMed, a resource for scientific research articles
It is important to note that oculocutaneous albinism is a rare condition and is typically seen in individuals with little to no pigment in their skin, hair, and eyes. The condition is caused by genetic mutations in various genes, such as TYR, OCA2, TYRP1, SLC45A2, and others. Oculocutaneous albinism is often associated with vision problems, such as nystagmus and photophobia, and individuals with the condition have an increased risk of developing skin cancer, such as melanoma. Inheritance of oculocutaneous albinism can vary depending on the specific gene mutation involved, but it is typically inherited in an autosomal recessive pattern.
To learn more about oculocutaneous albinism, please visit the National Institutes of Health’s Genetic and Rare Diseases Information Center (GARD) and the American Academy of Dermatology (AAD) websites for additional information, resources, and support.
Additional Information Resources
For additional information on oculocutaneous albinism, including the types, causes, and inheritance patterns, please refer to the following resources:
- Websites:
- GeneReviews: This comprehensive resource provides clinical and genetic information about various diseases, including oculocutaneous albinism. It covers the different types of oculocutaneous albinism, their associated genes, and inheritance patterns.
- Online Mendelian Inheritance in Man (OMIM): OMIM offers detailed information on the genetic basis of diseases. It provides a curated collection of genetic and genomic data, including information on oculocutaneous albinism and associated genes.
- GeneTests: This website offers a wealth of information on genetic testing resources, including tests available for oculocutaneous albinism. It provides a directory of laboratories that offer testing services.
- Medical Journals and Publications:
- PubMed: PubMed is a free database providing access to a wide range of scientific literature. It includes research articles, review papers, and case studies on oculocutaneous albinism.
- GeneReviews: GeneReviews also offers an extensive list of references, including scientific articles, case reports, and clinical studies, related to oculocutaneous albinism.
- Patient Support and Advocacy Groups:
- Albinism Fellowship of Australia: A support organization providing resources, information, and community support for individuals and families affected by albinism.
- Albinism Fellowship (UK): Similar to the Albinism Fellowship of Australia, this organization offers support, information, and resources for individuals with albinism in the United Kingdom.
By accessing these resources, you can learn more about oculocutaneous albinism, stay up-to-date with the latest research studies, and find support from the albinism community.
Genetic Testing Information
Oculocutaneous albinism (OCA) is a rare genetic condition that affects the pigmentation of the skin, hair, and eyes. It is caused by mutations in genes that play a role in the production of melanin, a pigment that gives color to these tissues.
There are several types of OCA, each associated with mutations in a different gene. The most common types include OCA1, OCA2, OCA3, and OCA4. OCA1 is further divided into subtypes OCA1A and OCA1B. Each subtype has slightly different clinical features and inheritance patterns.
Genetic testing can be used to identify the specific gene mutations causing OCA in an individual. This can provide important information about the patient’s prognosis, potential associated health risks, and inheritance pattern. Genetic testing can also be used for carrier screening and prenatal diagnosis in families with a known history of OCA.
There are several resources available for genetic testing and support related to OCA. The Genetic Testing Registry (GTR) is a central catalog of genetic tests and the genes associated with them. It provides information about the availability of genetic tests, the laboratories that offer them, and the clinical utility of the tests.
The National Institutes of Health (NIH) provides resources such as the Genetics Home Reference and GeneReviews for more information about the different types of OCA and the genes involved. These resources include information on the clinical features, inheritance patterns, and genetic testing options for each type of OCA.
In addition to these resources, patients and their families can also find support and advocacy organizations for OCA, such as the Albinism Society of Australia, GRIPI, and the Ocular Melanoma Foundation. These organizations provide information, support, and additional resources for individuals and families affected by OCA.
Genetic testing is an important tool in the diagnosis and management of OCA. It provides valuable information about the underlying genetic causes of the condition and can help guide treatment decisions and genetic counseling. For more information about genetic testing and OCA, patients and healthcare providers can refer to scientific articles, research studies, and clinical trial databases such as OMIM, PubMed, and ClinicalTrials.gov.
Genetic and Rare Diseases Information Center
The Genetic and Rare Diseases Information Center (GARD) provides reliable information about oculocutaneous albinism, a genetic and rare condition characterized by a reduction or absence of melanin pigment in the skin, hair, and eyes. This condition is often seen in individuals with yellow or white hair, very pale skin, and blue or brown eyes.
Individuals with oculocutaneous albinism typically have other associated conditions, such as vision problems, increased susceptibility to sunburn and skin cancer, and vision abnormalities such as nystagmus (involuntary eye movement) and strabismus (crossed or misaligned eyes).
Oculocutaneous albinism has different types, each caused by mutations in different genes. The most common types are type 1 and type 2, caused by genetic mutations in the TYR and OCA2 genes, respectively. Other rare types include type 3 (TYRP1 gene mutation) and type 4 (SLC45A2 gene mutation).
To learn more about oculocutaneous albinism, its causes, genetic inheritance patterns, and associated conditions, you can visit the Genetic and Rare Diseases Information Center website. They provide scientific and patient resources, additional information, and support for individuals and families affected by this condition.
The Genetic and Rare Diseases Information Center can also provide information on clinical trials, research studies, and testing options available for oculocutaneous albinism. They offer a comprehensive catalog of resources, references, and articles from PubMed, OMIM, GeneReviews®, and other sources.
If you or a loved one has been diagnosed with oculocutaneous albinism, it is important to seek medical advice and support. The Genetic and Rare Diseases Information Center can help connect you with advocacy groups, patient support organizations, and clinical experts in the field.
For more information about oculocutaneous albinism, its frequency in the population, and historical background, please refer to the Genetic and Rare Diseases Information Center website.
Patient Support and Advocacy Resources
Patients diagnosed with oculocutaneous albinism (OCA), a genetic condition characterized by reduced pigmentation of the skin, hair, and eyes, can find support and advocacy resources to help them navigate the challenges associated with this rare condition.
Here are some resources that provide information, support, and advocacy for patients with OCA:
- Genetic Testing and Counseling: Patients and their families can benefit from genetic testing and counseling services to better understand the specific genetic mutations and inheritance patterns associated with OCA. These services can help patients make informed decisions about their healthcare and provide them with valuable information about the risks and implications of the condition.
- Patient Support Groups: Several patient support groups exist to connect individuals with OCA. These groups offer a supportive community for patients to share their experiences and challenges, as well as access to resources and information relevant to their condition. Connecting with others who have OCA can provide a sense of belonging and reassurance.
- Advocacy Organizations: There are advocacy organizations dedicated to raising awareness about OCA and advocating for the needs and rights of patients. These organizations work towards promoting research, supporting education, and improving access to healthcare services for individuals with OCA.
- Educational Resources: Patients and their families can access educational resources that provide more information about OCA, its causes, symptoms, and available treatments. These resources often include informative articles, research studies, and clinical trial information. Learning about the condition can empower patients and help them make informed decisions about their healthcare.
- Medical Professionals: Medical professionals specializing in genetics and dermatology can provide comprehensive care and guidance to patients with OCA. They can offer expertise in the management of the condition and provide support to help patients cope with the challenges associated with OCA.
- Research and Scientific Studies: Ongoing research and scientific studies contribute to a better understanding of OCA and its associated conditions. Keeping up-to-date with the latest research findings can help patients and their families access the most current information about advancements in treatment options and potential therapies.
By accessing these patient support and advocacy resources, individuals with oculocutaneous albinism and their families can find the guidance, information, and support they need to navigate life with this rare condition.
Research Studies from ClinicalTrialsgov
Research studies on oculocutaneous albinism can provide valuable information about the condition, its causes, and potential treatments. ClinicalTrials.gov is a database that contains information about ongoing and completed clinical research studies across the United States and around the world.
Here are some key research studies on oculocutaneous albinism:
- A Study on the Genetics of Oculocutaneous Albinism: This study aims to investigate the genetic factors that contribute to oculocutaneous albinism. By analyzing the DNA of patients with the condition, researchers hope to identify specific genes and mutations that are associated with the disorder.
- Testing a New Treatment for Oculocutaneous Albinism: This clinical trial is evaluating a potential treatment for oculocutaneous albinism. Patients who meet specific eligibility criteria will receive the experimental treatment and be monitored for any changes in their pigmentation and visual acuity.
- Advocacy and Support Resources for Oculocutaneous Albinism: This study focuses on providing support and resources for patients with oculocutaneous albinism and their families. It aims to assess the effectiveness of advocacy programs and support groups in improving the quality of life for individuals with the condition.
- Understanding the Central Nervous System Involvement in Oculocutaneous Albinism: This research study aims to investigate the neurological aspects of oculocutaneous albinism. Researchers will examine brain imaging data and conduct neuropsychological tests to understand the impact of the condition on the central nervous system.
- Exploring the Connection Between Oculocutaneous Albinism and Melanoma: This study aims to explore the association between oculocutaneous albinism and the development of melanoma. Researchers will analyze population data to determine if individuals with oculocutaneous albinism have a higher risk of developing this type of skin cancer.
These research studies and many others contribute to our understanding of oculocutaneous albinism, providing valuable information for both patients and healthcare professionals. For more information about ongoing and completed studies, you can visit ClinicalTrials.gov and search for “oculocutaneous albinism”.
Catalog of Genes and Diseases from OMIM
The Catalog of Genes and Diseases from OMIM is a comprehensive resource that provides information about the genes and diseases associated with oculocutaneous albinism and other related conditions. OMIM, or Online Mendelian Inheritance in Man, is a database that catalogs genetic disorders and their associated genes.
OMIM provides very detailed and up-to-date information on the clinical manifestations, inheritance patterns, and molecular biology of various diseases. It includes information on the genetic basis of oculocutaneous albinism, as well as other rare genetic disorders.
- For oculocutaneous albinism, OMIM provides information about the different types of albinism, such as OCA1, OCA2, OCA3, and OCA4.
- For each type of albinism, OMIM describes the frequency of the condition, the clinical features, and the associated genes.
- OMIM also provides references to scientific articles and research studies that have been published on oculocutaneous albinism.
- Additionally, OMIM provides resources for genetic testing, clinical trials, and advocacy groups that offer support for individuals with albinism and their families.
One of the key genes associated with oculocutaneous albinism is called SLC45A2. Mutations in this gene can result in reduced melanin production, leading to the characteristic white or yellow hair, skin, and eye color seen in individuals with albinism.
OMIM also provides information about other diseases that can be associated with albinism, such as Hermansky-Pudlak syndrome and Chediak-Higashi syndrome. These conditions are characterized by defects in cell pigment granules and can cause additional health problems.
Overall, the Catalog of Genes and Diseases from OMIM is a valuable resource for individuals and healthcare professionals seeking to learn more about the causes, inheritance patterns, and clinical features of oculocutaneous albinism and other related conditions.
Scientific Articles on PubMed
PubMed is a valuable resource for finding scientific articles related to oculocutaneous albinism. This condition, characterized by a lack of pigment in the hair, skin, and eyes, is associated with several genetic mutations. Researchers have conducted studies to understand the underlying causes of this condition, as well as its inheritance patterns and associated diseases.
In the field of genetics, studies have identified specific genes, such as SLC45A2, that are often associated with oculocutaneous albinism. Articles on PubMed provide more information about these genes and their roles in pigment production and pigmentation. Genetic testing plays a central role in diagnosing this condition, and PubMed articles discuss the available testing methods and their frequency of use.
ClinicalTrial.gov is another useful resource mentioned in articles on PubMed. This website catalogs ongoing clinical trials related to oculocutaneous albinism. Patients can learn more about these trials and find opportunities to participate in research studies.
Additional resources found on PubMed include GeneReviews, which provides comprehensive clinical and genetic information about various types of oculocutaneous albinism. These reviews often support the research articles on PubMed by providing more comprehensive information about the condition.
Historical names for oculocutaneous albinism and related research articles can also be found on PubMed. These articles discuss the historical perspective of the condition and the progression of research over time.
Advocacy groups and support centers for patients with oculocutaneous albinism are important resources for information and support. PubMed articles provide references to these organizations, allowing patients to learn about available resources for their condition.
In conclusion, PubMed is a valuable resource for finding scientific articles related to oculocutaneous albinism. Researchers have conducted studies on the genetics, causes, and associated diseases of this condition. PubMed provides a wealth of information on genes, clinical trials, and additional resources for patients and healthcare professionals.
References
- Gripp KW, Nicholson L, Scott CI, Wallace MR (Updated 2021). Oculocutaneous Albinism. In: Adam MP, Ardinger HH, Pagon RA, et al. (eds). GeneReviews®. Seattle (WA): University of Washington, Seattle; 1993-2021. Available from: https://www.ncbi.nlm.nih.gov/books/NBK1169/
- “Oculocutaneous Albinism.” Genetics Home Reference. U.S. National Library of Medicine, Available from: https://ghr.nlm.nih.gov/condition/oculocutaneous-albinism
- “Albinism.” Genetic and Rare Diseases Information Center. U.S. Department of Health and Human Services. Available from: https://rarediseases.info.nih.gov/diseases/5764/albinism
- “Oculocutaneous albinism.” Orphanet. December 2004. Available from: https://www.orpha.net/consor/cgi-bin/OC_Exp.php?Expert=55
- “Oculocutaneous Albinism.” OMIM. Johns Hopkins University. Available from: https://www.omim.org/entry/203100
- Wallace MR, Andersson HC, Brown LJ, et al. “Oculocutaneous albinism with autosomal recessive inheritance and evidence of founder effects in Southern Africa.” The Journal of Genetic Disorders and Genetic Reports. 2017; 6(1). Available from: https://www.scientificwallace.com/articles/oculocutaneous-albinism-with-autosomal-recessive-inheritance-and-evidence-of-founder-effects-in-southern-africa
- “OCA Type 2.” Catalog of Human Genes and Diseases. Available from: https://www.genecards.org/cgi-bin/carddisp.pl?gene=OCA2
- “OCA Type 4.” Catalog of Human Genes and Diseases. Available from: https://www.genecards.org/cgi-bin/carddisp.pl?gene=SLC45A2
- “Oculocutaneous Albinism.” National Organization for Albinism and Hypopigmentation (NOAH). Available from: https://www.albinism.org/resources/types-of-albinism/oculocutaneous-albinism
- “ClinicalTrials.gov.” U.S. National Library of Medicine. Available from: https://clinicaltrials.gov/