Jackson-Weiss Syndrome is a hereditary disease that affects the skull, face, and feet. It is inherited in an autosomal dominant manner.
One characteristic of JWS is an unusual skull shape. This leads to an abnormally shaped face, usually a small midface. The toes are also very wide and webbed between the second and third toe. Some of the bones may be fused together as well.
The reason for the abnormally shaped skull is due to the fact that portions of the skull fuse together too early.
Jackson-Weiss syndrome is inherited in an autosomal dominant manner. This means that possession of only one copy of the defective gene is enough to cause disease. When a parent has Jackson-Weiss syndrome each of his or her children have a 50% chance to inherit the disease-causing mutation. JWS is believed to have a high rate of penetrance. This means that almost all people who inherit the altered gene will manifest symptoms. JWS has also occurred spontaneously in babies with no family history of it or any similar disorder. This is known as a sporadic occurrence. Most commonly, JWS is associated with changes in FGFR2.
I am not exactly sure what you are looking for, but the only "j" disease that I am familiar with in regards to that letter is Jackson Weiss Syndrome. This affects feet and other bones relating to fusions of the bones. The most common bones that are fused are relating to the skull. This prevents the effected individual's skull to grow with age and also may demonstrate mental retardation, seizures (from the skull pressure), and sometimes vision issues. The eyes are far apart (as in fetal alcohol syndrome), and the person may often exhibit a "bulging" forehead.
In addition to Jackson Weiss, there is one additional, quite rare disorder. This is Joubert Syndrome.
"Joubert syndrome is a rare brain malformation characterized by the absence or underdevelopment of the cerebellar vermis - an area of the brain that controls balance and coordination. The most common features of Joubert syndrome in infants include abnormally rapid breathing (hyperpnea), decreased muscle tone (hypotonia), jerky eye movements (oculomotor apraxia), mental retardation, and the inability to coordinate voluntary muscle movements (ataxia). Physical deformities may be present, such as extra fingers and toes (polydactyly), cleft lip or palate, and tongue abnormalities. Kidney and liver abnormalities can develop, and seizures may also occur.. Most cases of Joubert syndrome are sporadic (not inherited). In some families, however, Joubert syndrome appears to be inherited in an autosomal recessive manner (meaning both parents must have a copy of the mutation) via mutation in a number of genes, including NPHP1, AHI1, and CEP290. "