Ciliopathies are diseases of genetic origin that cause morphological and functional alterations in many parts of the body. In this article we will describe Symptoms and causes of Bardet-Biedl syndrome one of the most common ciliopathies, which causes progressive loss of vision and kidney disorders, among other problems.
Bardet-Biedl syndrome is a type of ciliopathy , a group of genetic diseases that involve alterations in the primary cilia of cells. Other common ciliopathies are polycystic kidney disease, nephronophthisis, Joubert syndrome, Leber congenital amaurosis, orofaciodigital syndrome, asphyxiating thoracic dystrophy, and Alström syndrome.
Among the signs of ciliopathies, the degeneration of retinal tissue, the presence of brain abnormalities and the development of kidney diseases stand out. Obesity, diabetes and skeletal dysplasia (morphological abnormalities in bone cells) are also common consequences of genetic defects in ciliary protein synthesis
Bardet-Biedl syndrome affects approximately 1 in 150,000 people. Its specific manifestations vary depending on the case due to the great genetic variability of the defects that cause this disease.
Causes of this disorder
To date, at least 16 genes that are associated with Bardet-Biedl disease In most cases, the alterations are caused by mutations in several of the genes involved; This causes the signs to vary greatly. Defects in the MKS gene appear to lead to especially severe variants of the disorder.
However, around a fifth of cases do not have mutations in any of these genes, which suggests that in the future others related to the same signs and symptoms will be found.
These genetic defects cause the proteins that allow the synthesis and correct functioning of primary cilia, structures found in different cells. This causes malformations and problems in the eyes, kidneys, face or genitals, among other parts of the body.
Bardet-Biedl syndrome It is associated with McKusick-Kaufman disease, which is transmitted by autosomal recessive inheritance and is characterized by the presence of postaxial polydactyly, congenital heart disease and hydrometrocolpos (cystic dilation of the vagina and uterus that causes fluid accumulation). The differential diagnosis between both disorders can be complex.
Main symptoms and signs
There are many alterations that can appear as a consequence of defects in the cilia. We will focus on the most characteristic and relevant ones, although we will mention most of the
1. Cone-rod dystrophy (retinitis pigmentosa)
Retinitis or pigmentary retinopathy is one of the most characteristic signs of ciliopathies; It occurs in more than 90% of cases. It involves a progressive loss of vision which begins with lack of visual acuity and night blindness and continues after childhood, in some cases reaching lack of vision in adolescence or adulthood.
2. Postaxial polydactyly
Another key sign is the presence of an extra finger on the hands or toes , which occurs in 69% of people with Bardet-Biedl syndrome. In some cases the fingers are shorter than normal (brachydactyly) and/or are fused together (syndactyly).
In more than 70% of cases, obesity occurs from two or three years of age; it is common for them to develop hypertension, hypercholesterolemia and type 2 diabetes mellitus due. This type of obesity is also considered a key sign.
4. Kidney disorders
Bardet-Biedl syndrome increases the risk of various kidney diseases: polycystic kidneys, renal dysplasia, nephronophthisis (or tubular cystic disease), and focal segmental glomerulosclerosis. Sometimes alterations also appear in the lower part of the urinary tract, such as bladder detrusor dysfunctions.
5. Hypogonadism
Hypogonadism consists of deficient production of sex hormones , which causes sexual characteristics to not develop in a normative way. This alteration also causes sterility and is more common in men with the syndrome.
6. Developmental disorders
It is common for them to occur delays in development, language, speech and motor skills , as well as cognitive deficits (generally moderate) as a consequence of ciliary dysfunctions. These problems usually cause alterations of varying severity in learning, social interaction, and self-management.
7. Other symptoms
There are many other common symptoms and signs in Bardet-Biedl syndrome, although they are not considered fundamental features of the disease. Among these we find behavioral and psychological alterations such as sudden attacks of anger and lack of emotional maturity.
Alterations in the size of the head and the malformations in teeth and face , especially in the nose area. Partial or total loss of smell (anosmia) also appears in some cases.
Hirschsprung disease frequently appears as a consequence of Bardet-Biedl disease. It is a disorder of the large intestine that makes intestinal transit difficult, causing constipation, diarrhea and vomiting. Sometimes it can cause severe gastrointestinal problems, especially in the colon.
