North Carolina macular dystrophy (NCMD, MCDR1) is a congenital autosomal dominant trait that appears to be completely penetrant. It is generally nonprogressive. The ophthalmoscopic findings are highly variable and are always much more dramatic than one would predict from the relatively good visual acuity level, which ranges from 20/20 to 20/400 (median, 20/60). Patients may have only a few drusen in the central macular region (grade I), confluent drusen confined to the central macular region (grade II), or a severe macular coloboma/staphyloma (grade III) involving 3 to 4 disc areas of the central macular region. Choroidal neovascular membranes develop in some patients. Color vision is normal. Electrophysiologic studies are also normal (summary by Small, 1998). Genetic Heterogeneity of Retinal Macular Dystrophy MCDR2 (608051) is caused by mutation in the PROM1 gene (604365) on chromosome 4p15. MCDR3 (608850) is caused by a duplication on chromosome 5p15. MCDR4 (619977) is caused by mutation in the CLEC3B gene (187520) on chromosome 3p21. MCDR5 (see 613660) is caused by mutation in the CDHR1 gene (609502) on chromosome 10q23. See MAPPING for possible additional loci for MCDR.

Retinitis pigmentosa (RP) describes a group of disorders with progressive degeneration of rod and cone photoreceptors in a rod-cone pattern of dysfunction. RP has a prevalence of 1 in 3,500, and is genetically and phenotypically heterogeneous (summary by Mackay et al., 2010). For a general phenotypic description and a discussion of genetic heterogeneity of retinitis pigmentosa, see 268000.

Progressive retinal dystrophy due to retinol transport defect is a rare, genetic, metabolite absorption and transport disorder characterized by progressive rod-cone dystrophy, usually presenting with impaired night vision in childhood, progressive loss of visual acuity and severe retinol deficiency without keratomalacia. Association with ocular colobomas, severe acne and hypercholesterolemia has been reported.

TRNT1 deficiency encompasses what was first thought to be two separate disorders, a severe disorder called sideroblastic anemia with B-cell immunodeficiency, periodic fevers, and developmental delay (SIFD) and a milder disorder called retinitis pigmentosa with erythrocytic microcytosis (RPEM), each named for its most common features. SIFD begins in infancy, and affected individuals usually do not survive past childhood. RPEM, on the other hand, is recognized in early adulthood, and the microcytosis usually does not cause any health problems. However, it has since been recognized that some individuals have a combination of features that fall between these two ends of the severity spectrum. All of these cases are now considered part of TRNT1 deficiency.\n\nIn addition, many individuals with TRNT1 deficiency have recurrent fevers that are not caused by an infection. These fever episodes are often one of the earliest recognized symptoms of TRNT1 deficiency, usually beginning in infancy. The fever episodes are typically accompanied by poor feeding, vomiting, and diarrhea, and can lead to hospitalization. In many affected individuals, the episodes occur regularly, arising approximately every 2 to 4 weeks and lasting 5 to 7 days, although the frequency can decrease with age.\n\nMany people with TRNT1 deficiency have an immune system disorder (immunodeficiency) that can lead to recurrent bacterial infections. Repeated infections can cause life-threatening damage to internal organs. The immunodeficiency is characterized by low numbers of immune system cells called B cells, which normally help fight infections by producing immune proteins called antibodies (or immunoglobulins). These proteins target foreign invaders such as bacteria and viruses and mark them for destruction. In many individuals with TRNT1 deficiency, the amount of immunoglobulins is also low (hypogammaglobulinemia).\n\nA common feature of TRNT1 deficiency is a blood condition called sideroblastic anemia, which is characterized by a shortage of red blood cells (anemia). In TRNT1 deficiency, the red blood cells that are present are unusually small (erythrocytic microcytosis). In addition, developing red blood cells in the bone marrow (erythroblasts) can have an abnormal buildup of iron that appears as a ring of blue staining in the cell after treatment in the lab with certain dyes. These abnormal cells are called ring sideroblasts.\n\nTRNT1 deficiency is a condition that affects many body systems. Its signs and symptoms can involve blood cells, the immune system, the eyes, and the nervous system. The severity of the signs and symptoms vary widely.\n\nNeurological problems are also frequent in TRNT1 deficiency. Many affected individuals have delayed development of speech and motor skills, such as sitting, standing, and walking, and some have low muscle tone (hypotonia).\n\nEye abnormalities, often involving the light-sensing tissue at the back of the eye (the retina), can occur in people with TRNT1 deficiency. Some of these individuals have a condition called retinitis pigmentosa, in which the light-sensing cells of the retina gradually deteriorate. Eye problems in TRNT1 deficiency can lead to vision loss.\n\nFeatures that occur less commonly in people with TRNT1 deficiency include hearing loss caused by abnormalities of the inner ear (sensorineural hearing loss), recurrent seizures (epilepsy), and problems with the kidneys or heart.

Hypotaurinemic retinal degeneration and cardiomyopathy (HTRDC) is an autosomal recessive disorder characterized by low plasma taurine, childhood-onset progressive retinal degeneration, and cardiomyopathy (Ansar et al., 2020).