Some blind people are skilled at echolocating silent objects simply by producing mouth clicks and listening to the returning echoes. It has been shown that blind echolocation experts use what is normally the "visual" part of their brain to process the echoes.Government actions are sometimes taken to make public places more accessible to blind people. Public transportation is freely available to blind people in many cities. Tactile paving and audible traffic signals can make it easier and safer for visually impaired pedestrians to cross streets. In addition to making rules about who can and cannot use a cane, some governments mandate the right-of-way be given to users of white canes or guide dogs. Reading and magnification
Most visually impaired people who are not totally blind read print, either of a regular size or enlarged by magnification devices. Many also read large-print, which is easier for them to read without such devices. A variety of magnifying glasses, some handheld, and some on desktops, can make reading easier for them. Others read braille (or the infrequently used Moon type), or rely on talking books and readers or reading machines, which convert printed text to speech or braille. They use computers with special hardware such as scanners and refreshable braille displays as well as software written specifically for the blind, such as optical character recognition applications and screen readers.
Carnosinemia is a rare autosomal recessive metabolic disorder caused by a deficiency of carnosinase, a dipeptidase (a type of enzyme that splits dipeptides into their two amino acid constituents).Carnosine is a dipeptide composed of beta-alanine and histidine, and is found in skeletal muscle and cells of the nervous system. This disorder results in an excess of carnosine in the urine, cerebrospinal fluid, blood, and nervous tissue. Neurological disorders associated with a deficiency of carnosinase, and the resulting carnosinemia ("carnosine in the blood") are common. Symptoms and signs
A variety of neurological symptoms have been associated with carnosinemia. They include: hypotonia, developmental delay, intellectual disability, degeneration of axons, sensory neuropathy, tremors, demyelinization, gray matter anomalies, myoclonic seizures, and loss of purkinje fibers. Genetics
The gene for carnosinase is located on chromosome 18, an autosome. The carnosine dipeptidase-1 gene (CNDP1) controls tissue and serum carnosinase. Mutations in CNDP1 are  responsible for carnosinase deficiency, resulting in carnosinemia.Carnosinemia is an autosomal recessive disorder, which means the defective gene is located on an autosome, and two copies of the defective gene - one from each parent - are required to inherit the disorder. The parents of an individual with an autosomal recessive disorder both carry one copy of the defective gene, but usually do not experience any signs or symptoms of the disorder. Diagnosis
Types
Carnosinase in humans has two forms:1. Cellular, or tissue carnosinase: This form of the enzyme is found in every bodily tissue.