MedGen

Warfarin is an oral anti-coagulant used world-wide to treat and prevent thrombotic disorders. While it is highly effective, it has a very narrow therapeutic index making it difficult to dose correctly. Genetic variants in cytochrome P450-2C9 (CYP2C9), vitamin K-epoxide reductase complex (VKORC1), cytochrome P450-CYP4F2 (CYP4F2) and the CYP2C cluster (eg. rs12777823), along with non-genetic factors, are known to affect warfarin dose variability. Patients with specific variants in the gene CYP2C9 (the primary warfarin-metabolizing enzyme) may require a lower dose of warfarin as compared to patients without these variants. Patients with specific variants in VKORC1 (the target enzyme of warfarin) may require a lower warfarin dose as compared to patients who do not have these variants. The combination of CYP2C9/VKORC1/CYP4F2/CYP2C genetic variants, along with clinical factors, can put some patients at risk for therapeutic failure or adverse events such as bleeding. Guidelines regarding the use of pharmacogenomic tests in dosing for warfarin have been published in Clinical Pharmacology and Therapeutics by the Clinical Pharmacogenetics Implementation Consortium (CPIC) and are available on the CPIC and PharmGKB websites. [from PharmGKB]

Alpha-thalassemia X-linked intellectual disability (ATR-X) syndrome is characterized by distinctive craniofacial features, genital anomalies, hypotonia, and mild-to-profound developmental delay / intellectual disability (DD/ID). Craniofacial abnormalities include small head circumference, telecanthus or widely spaced eyes, short triangular nose, tented upper lip, and thick or everted lower lip with coarsening of the facial features over time. While all affected individuals have a normal 46,XY karyotype, genital anomalies comprise a range from hypospadias and undescended testicles, to severe hypospadias and ambiguous genitalia, to normal-appearing female external genitalia. Alpha-thalassemia, observed in about 75% of affected individuals, is mild and typically does not require treatment. Osteosarcoma has been reported in a few males with germline pathogenic variants. [from GeneReviews]

The thiopurines include azathioprine (a pro-drug for mercaptopurine), mercaptopurine and thioguanine. They are used to treat a variety of immunological disorders such as rheumatoid arthritis, non- Hodgkin lymphoma and ulcerative colitis. Both mercaptopurine and thioguanine can exert cytotoxic effects through the formation of thioguanine nucleotides (TGNs), active metabolites that incorporate into DNA. Mercaptopurine and thioguanine are directly inactivated by thiopurine S-methyltransferase (TPMT). Individuals with two nonfunctional TPMT alleles are at 100% risk of potentially fatal myelosuppression, due to an increased buildup of toxic TGNs. Alternative agents or a drastically reduced dose are recommended for patients with this genotype. Patients heterozygous for a nonfunctional TPMT allele are at increased risk of myelosuppression, and reduced dosing is recommended for these individuals. These dosing guidelines have been published in Clinical Pharmacology and Therapeutics by the Clinical Pharmacogenetics Implementation Consortium (CPIC) and are available on the PharmGKB website. [from PharmGKB]

Yunis-Varon syndrome (YVS) is a severe autosomal recessive disorder characterized by skeletal defects, including cleidocranial dysplasia and digital anomalies, and severe neurologic involvement with neuronal loss. Enlarged cytoplasmic vacuoles are found in neurons, muscle, and cartilage. The disorder is usually lethal in infancy (summary by Campeau et al., 2013). [from OMIM]

Chanarin-Dorfman syndrome (CDS) is a rare autosomal recessive nonlysosomal inborn error of neutral lipid metabolism. Patients present with a nonbullous erythrodermic form of ichthyosis (NCIE; see 242300) with variable involvement of other organs, such as liver, central nervous system, eyes, and ears. Intracellular triacylglycerol droplets are present in most tissues, and diagnosis can be confirmed by a simple blood smear, in which the characteristic lipid droplets are observed in the cytoplasm of granulocytes (summary by Lefevre et al., 2001). Another form of neutral lipid storage disease without ichthyosis but with myopathy (NLSDM; 610717) is caused by mutation in the PNPLA2 gene (609059). [from OMIM]

Klippel-Trenaunay syndrome is a condition that affects the development of blood vessels, soft tissues (such as skin and muscles), and bones. The disorder has three characteristic features: a red birthmark called a port-wine stain, abnormal overgrowth of soft tissues and bones, and vein malformations.

Most people with Klippel-Trenaunay syndrome are born with a port-wine stain. This type of birthmark is caused by swelling of small blood vessels near the surface of the skin. Port-wine stains are typically flat and can vary from pale pink to deep maroon in color. In people with Klippel-Trenaunay syndrome, the port-wine stain usually covers part of one limb. The affected area may become lighter or darker with age. Occasionally, port-wine stains develop small red blisters that break open and bleed easily.

Klippel-Trenaunay syndrome is also associated with overgrowth of bones and soft tissues beginning in infancy. Usually this abnormal growth is limited to one limb, most often one leg. However, overgrowth can also affect the arms or, rarely, the torso. The abnormal growth can cause pain, a feeling of heaviness, and reduced movement in the affected area. If the overgrowth causes one leg to be longer than the other, it can also lead to problems with walking.

Malformations of veins are the third major feature of Klippel-Trenaunay syndrome. These abnormalities include varicose veins, which are swollen and twisted veins near the surface of the skin that often cause pain. Varicose veins usually occur on the sides of the upper legs and calves. Veins deep in the limbs can also be abnormal in people with Klippel-Trenaunay syndrome. Malformations of deep veins increase the risk of a type of blood clot called a deep vein thrombosis (DVT). If a DVT travels through the bloodstream and lodges in the lungs, it can cause a life-threatening blood clot known as a pulmonary embolism (PE).

Other complications of Klippel-Trenaunay syndrome can include a type of skin infection called cellulitis, swelling caused by a buildup of fluid (lymphedema), and internal bleeding from abnormal blood vessels. Less commonly, this condition is also associated with fusion of certain fingers or toes (syndactyly) or the presence of extra digits (polydactyly). [from MedlinePlus Genetics]

A rare primary immunodeficiency due to a defect in innate immunity characterized by a marked decrease or absence of myeloperoxidase activity in neutrophils and monocytes. Clinically, most patients are asymptomatic. Occasionally, severe infectious complications may occur, particularly recurrent candida infections, being especially severe in the setting of comorbid diabetes mellitus. [from ORDO]

A rare genetic primary immunodeficiency with characteristics of increased susceptibility to fungal infections that typically manifest as recurrent, chronic mucocutaneous candidiasis, systemic candidiasis with meningoencephalitis and deep dermatophytosis. Dermatophytes invade skin, hair, nails, lymph nodes and brain, resulting in erythematosquamous lesions, nodular subcutaneous or ulcerative infiltrations, severe onychomycosis and lymphadenopathy. [from SNOMEDCT_US]

A rare immune complex-mediated vasculitis characterized by the presence of circulating cryoprecipitable immune complexes in the serum, manifesting clinically with the classical triad of purpura, weakness and arthralgia. [from ORDO]

Abnormally low level of eosinophils in the blood. [from NCI]

An abnormality of the hematopoietic system. [from HPO]