The separate subdivisions are categorized by the genes that they effect. The seven types are not evenly distributed amongst ethnic groups with OCA1 being the subtype most prominent in Caucasians - "accounting for approximately 50% of cases worldwide. "Previously, diagnosis was done from observation of hypopigmentation which is obvious at birth, but this is now insufficient early on to distinguish between the seven major types of OCA.Prenatal testing has been achieved through fetal skin biopsy followed by subsequent histologic and electron microscope examination for melanin levels. Clinical findings have established that molecular genetic testing of TYR, the gene encoding tyrosinase, can distinguish between 1A and 1B because the phenotypes can be identical during the first year of life. OCA1A results in complete loss of tyrosinase enzyme activity. Individuals with 1B will experience increased pigmentation with age because they have a very low level of melanin production that can increase. The histological approach for prenatal diagnosis is useful for all families at risk for OCA1 whereas the molecular genetic test is only helpful when at least one mutation is known. Management
There is currently no treatment for this disease. The extremely hypopigmented skin that is characteristic in OCA1 particularly leads to risk of skin damage and non-melanotic skin cancers due to increased sensitivity to UV rays. In OCA1B, because there is some presence of melanin, it grows with age and pigmentation can increase; the same cannot be said for OCA1A.
: 1 : 361 : 1 : 102 Diffuse TGCT occurs less frequently and is locally aggressive (in some cases, tumors may infiltrate surrounding soft tissue). : 245 : 1 : 102 : 1  It most commonly affects people under 40 years old, though the age of occurrence varies. : 102  Diffuse TGCT may occur inside a joint (intra-articular) or outside of a joint (extra-articular). Intra-articular tumors typically occur in the knee (approximately 75% of cases) and hip (approximately 15% of cases). : 102  Extra-articular tumors are usually found in the knee, thigh, and foot. : 101  Symptoms include swelling, pain, sensitivity, and/or limited range of motion. : 102  The rate of reoccurrence is estimated to be 18-46% for intra-articular tumors and 33-50% for extra-articular tumors. : 103 : 1

Complications
Diffuse TGCT is locally aggressive and can spread to surrounding tissues, causing bone erosion and tissue damage. If not treated early, it can spread to areas outside the joint, extra-articular, and potentially cause permanent loss of range as well as intense pain. Mechanism
TGCT tumors grow due to genetic overexpression of colony stimulating factor 1. This causes colony-stimulating factor-1 receptor (CSF1R) cells to accumulate in the joint tissue. Diagnosis
TGCT can be diagnosed by magnetic resonance imaging (MRI), by biopsy, or during surgery. The disorder is difficult to identify and is often not diagnosed for years due to nonspecific symptoms or a general paucity of symptoms. TGCT cases are often misdiagnosed as osteoarthritis, localized trauma, sports injuries, xanthomas, or other conditions. One study of 122 diffuse TGCT patients found that the average delay in diagnosis was 2.9 years.