Retinal Degeneration as Part of a Syndrome

The eye is a complex organ and vision loss is a common symptom of many complex diseases and syndromes which affect the human body

Bardet-Biedl syndrome (BBS) is a rare and genetically inherited disorder which causes a wide range of symptoms in the body. Bardet-Biedl can occur due to mutations in at least 14 genes (BBS genes) which are important in the development of cilia; finger-like projections which protrude out from many cell-types. Cilia are very important for facilitating cell-movement, in addition to being required for sensory perception (vision, hearing, smell).

Mutations in the BBS genes causes these cilia to develop incorrectly and malfunction, which has a major effect on many chemical signalling pathways and impact our senses.

There are a wide variety of symptoms which develop as a result of Bardet-Biedl syndrome, particularly vision loss due to deterioration of the retina and blind spots developing in peripheral vision, obesity and the excessive growth of fingers and toes (polydactyly). Other common signs of Bardet-Biedl syndrome include impaired speech, poor motor control which affects walking and infertility.

Alström syndrome is a rare and complex genetic disorder which is inherited in an autosomal recessive manner, where an affected individual has two copies of the ALMS1 gene.

It generally begins in early childhood and impacts a number of systems in the body, with vision loss due to cone-rod dystrophy a common feature of the condition. Progressive hearing loss, type-2 diabetes and heart disease are other symptoms which are frequently recognised in people living with Alström syndrome.

Wolfram syndrome is a condition which affects many body systems and exists in two forms, Wolfram syndrome type 1 and Wolfram syndrome type 2. Wolfram syndrome type 1 is caused by mutations in the WFS1 gene, while wolfram syndrome type 2 arises due to mutations in the CISD2 gene and share common symptoms, such as cell death in the optic nerve to eventually cause blindness, hearing loss caused by changes to the inner ear and neurological disorders.

People living with Wolfram syndrome type 2 also experience stomach ulcers. The severe health complications associated with Wolfram syndrome makes it a fatal disease, often by mid-adulthood.

Joubert syndrome is an inherited ciliopathy, meaning it is a condition caused by poorly structured and developed cilia, arising due to mutations in a wide number of genes, all of which have not yet been identified. Joubert syndrome is inherited in an autosomal recessive manner, and so two faulty gene copies must be present for the condition to develop.

Joubert syndrome is a developmental brain disorder and is characterised by an underdeveloped cerebellar vermis; the part of the brain responsible for coordination. As a result, many people living with Joubert syndrome have difficulty with controlling body movements (ataxia), with uncontrolled eye movements a very common feature and difficulty moving eyes for peripheral vision challenging (oculomotor ataxia).

Mainzer-Saldino syndrome is a genetic and rare ciliopathy, which means that it develops due to mutations in genes which have a fundamental role in cilia development. Mainzer-Saldino syndrome is caused by mutations in the IFT140 gene, which produces a protein that is involved in cilia formation and maintenance.

This condition is characterised by a deterioration in visual acuity, kidney problems and abnormal skeletal structures. Degeneration of the light-sensitive tissue at the back of the eye, called the retina occurs because the rod and cone photoreceptors which perceive light, contain cilia which have not developed correctly. Therefore, vision loss is a primary feature of this condition and can vary in time of onset, from infancy to childhood. The manner of this vision loss is also similar to that of Leber Congenital Amaurosis (LCA) and Rod-Cone dystrophies, although the pigment deposits evident in these dystrophies, for example, Retinitis Pigmentosa, are not present in Mainzer-Saldino syndrome.

Stickler syndrome is an inherited condition, which has two distinct forms, caused by mutations in the COL2A1 gene and COL11A1 gene respectively. These genes provide instructions to make collagen, which provides structure to the connective tissue of the body.

Therefore, people living with Stickler syndrome have a distinct flattened face because of undeveloped bone structures. Nearsightedness (myopia) and retinal detachment are other common symptoms, and may result in serious visual impairment and blindness for some people living with Stickler syndrome.

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