Since<unk>  is incurable at present, it is helpful to diagnose children well before they develop the characteristic night blindness. Some preliminary studies have suggested as many as 10% of congenitally deaf children may have<unk> . However, a misdiagnosis can have bad consequences. The simplest approach to diagnosing<unk>  is to test for the characteristic chromosomal mutations. An alternative approach is electroretinography, although this is often disfavored for children, since its discomfort can also make the results unreliable. Parental consanguinity is a significant factor in diagnosis.<unk>  I may be indicated if the child is profoundly deaf from birth and especially slow in walking. Thirteen other<unk> s may exhibit signs similar to<unk> , including Alport<unk> , Alström<unk> , Bardet–Biedl<unk> , Cockayne<unk> , spondyloepiphyseal dysplasia congenita, Flynn–Aird<unk> , Friedreich ataxia, Hurler<unk>  (MPS-1), Kearns–Sayre<unk>  (CPEO), Norrie<unk> , osteopetrosis (Albers–Schonberg disease), Refsum disease (phytanic acid storage disease) and Zellweger<unk>  (cerebrohepatorenal<unk> . Classification Although<unk>  has been classified clinically in several ways, the prevailing approach is to classify it into three clinical sub-types called<unk> her I, II and III in order of decreasing severity of deafness. Although it was previously believed that there was an<unk>  type IV, researchers at the University of Iowa recently confirmed that there is no<unk> H type IV. As described below, these clinical subtypes may be further subdivided by the particular gene mutated; people with<unk> her I and II may have any one of six and three genes mutated, respectively, whereas only one gene has been associated with<unk> her III. The function of these genes is still poorly understood.<unk>  is a variable condition; the degree of severity is not tightly linked to whether it is<unk> her I, II or III. For example, someone with type III may be unaffected in childhood but go on to develop a profound hearing loss and a very significant loss of sight by early-to-mid adulthood. Similarly, someone with type I, who is therefore profoundly deaf from birth, may keep good central vision until the sixth decade of life or even beyond. People with type II, who have<unk> eful hearing with a hearing aid, can experience a wide range of severity of the RP. Some may maintain good reading vision into their 60s, while others cannot see to read while still in their 40s. Since<unk>  is inherited in an autosomal recessive pattern, both males and females are equally likely to inherit it. Consanguinity of the parents is a risk factor.
Usher syndrome
Myhre syndrome
Sly syndrome
Irlen syndrome
McGillivray syndrome
Fabry disease
Bart syndrome
Sugarman syndrome