Treacher Collins syndrome--a facial disorder characterized by deformed ears, deafness, down-slanting eyes, a narrow, flat face, and a small chin--was found to be caused by a mutation in a gene on chromosome 5, which codes for a protein named Treacle.
Retinitis pigmentosa is a progressive form of blindness that affects one in 4,000 people. One of the two most common forms of the disease was traced to a gene on the X chromosome. Researchers are now developing a test for the disorder.
Anhidrotic ectodermal dysplasia leaves sufferers toothless, bald, and unable to sweat. A mutation on the X chromosome was found to be responsible. It interferes with the development of the ectoderm--the outermost cell layer in the human embryo.
Astrotactin is a protein that guides developing neurons to their correct positions in the embryonic brain. A gene for the protein was identified on chromosome 1. The find could lead to greater understanding of epilepsy and schizophrenia, which may sometimes result from errors in neuron migration.
Williams syndrome sufferers have relatively good language skills, but they often have problems with regard to spatial tasks--they have trouble building a model from a diagram, for instance. That specific disability was traced in 1996 to a missing gene on chromosome 7, which codes for a protein involved in brain development. People with Williams lack several other genes on the same chromosome.
Basal cell carcinoma, the most common form of skin cancer, was found to be caused by a mutation in a gene on chromosome 9 called patched. The normal version of the gene plays a role in embryonic development.
Fanconi anemia, a rare disorder, has been traced to a gene on chromosome 16. It’s thought that mutations in the gene cause an increased susceptibility to chemicals that damage DNA. Affected children are unable to produce sufficient blood cells and usually develop anemia or leukemia, typically dying by age 16.
Hemochromatosis, the most common inherited genetic disorder among people of European descent, was linked to a gene on chromosome 6. The mutation may disrupt the intestine’s ability to regulate the absorption of iron, which builds up in various organs. Sufferers can develop diabetes, cirrhosis, and heart disease.
Progressive myoclonus epilepsy is a rare form of inherited epilepsy characterized by nerve degeneration and progressive dementia. The gene that causes it was pinpointed on chromosome 21. It’s known that a mutation blocks the production of the enzyme cystatin B, but how this leads to epilepsy is still unclear.