In TPP, the mutations described are single-nucleotide polymorphisms located in the hormone response element responsive to thyroid hormone, implying that transcription of the gene and production of ion channels may be altered by increased thyroid hormone levels. Furthermore, mutations have been reported in the genes coding for potassium voltage-gated channel, Shaw-related subfamily, member 4 (Kv3.4) and sodium channel protein type 4 subunit alpha (Na41.4).Of people with TPP, 33% from various populations were demonstrated to have mutations in KCNJ18, the gene coding for Kir2.6, an inward-rectifier potassium ion channel. This gene, too, harbors a thyroid response element.Certain forms of human leukocyte antigen (HLA)—especially B46, DR9, DQB1*0303, A2, Bw22, AW19, B17, and DRW8—are more common in TPP. Linkage to particular forms of HLA, which plays a central role in the immune response, might imply an immune system cause, but it is uncertain whether this directly causes TPP or whether it increases the susceptibility to Graves disease, a known autoimmune disease. Thyroid disease
The most common underlying form of thyroid disease associated with TPP is Graves disease, a syndrome due to an autoimmune reaction that leads to overproduction of thyroid hormone. TPP has also been described in people with other thyroid problems such as thyroiditis, toxic nodular goiter, toxic adenoma, TSH-producing pituitary adenoma, excessive ingestion of thyroxine or iodine, and amiodarone-induced hyperthyroidism. Mechanism
The muscle weakness and increased risk of irregular heart beat in TPP result from markedly reduced levels of potassium in the bloodstream.
Abnormalities of the chest: either pectus carinatum; a protruding sternum, or pectus excavatum; a sunken sternum form an immediately recognizable sign of fetal warfarin syndrome. Congenital heart defects such as a thinned atrial septum, coarctation of the aorta, patent ductus arteriosus; a connection between the pulmonary artery and aorta occur in 8% of fetal warfarin syndrome patients. Situs inversus totalis, the complete left-right mirroring of thoracic organs, has also been observed

CNS
Defects of the central nervous system can lead to profound intellectual disabilities. Fetal warfarin syndrome can lead to microcephaly; an abnormally small head, hydrocephaly; increased ventricle size and CSF volume, and agenesis of the corpus callosum. These defects contribute to the appearance of significant intellectual disability in 31% of fetal warfarin syndrome cases. Hypotonia, whole body muscle relaxation, can appear in newborns with severe nervous deficits. Atrophy of the optic nerve can also cause blindness in fetal warfarin syndrome. Physiological
Inhibition of coagulation and resultant internal bleeding can cause too few red blood cells to be present in the bloodstream and low blood pressure in newborns with fetal warfarin syndrome. Low hemoglobin levels can lead to partial oxygen starvation, a high level of lactic acid in the bloodstream, and acidosis. Prolonged oozing of fluid from the stump of the cut umbilical cord is common. Cause
Fetal warfarin syndrome appears in greater than 6% of children whose mothers took warfarin during pregnancy. Warfarin has a low molecular weight so can pass from the maternal to fetal bloodstream through the tight filter-like junctions of the placental barrier.