Laurence-Moon-Bardet-Biedl syndrome (LMBBS) is an autosomal recessive genetic disorder characterized by obesity, retinal degeneration, extra digits on the hands and feet, and intellectual impairment. In an autosomal recessive disorder, both parents must be carriers of the defective gene and both must pass on the defect to the child in order for the child to be affected. If both parents carry the defective gene responsible for causing LMBBS, they have a 1 in 4 chance of having a child with the syndrome.
In 1993, the gene responsible for LMBBS was located on chromosome 16q21 (type 2). Shortly thereafter, another gene on chromosome 11q13 (type 1) was identified. Since then, two others were found on chromosomes 3p12 (type 3) and 15q22 (type 4). The most common form of LMBBS is type 1 and the most rare form is type 3. It is expected, however, that another gene that causes the syndrome also exists because there are identified cases that have none of these four defects. The occurrence rate varies in different parts of the world. In regions such as Kuwait, the occurrence is 1 in 13,500 due to a high frequency of inter-family marriages. British studies, on the other hand, show the prevalence to be 1 in 160,000. While this syndrome is considered rare, it is suspected that there is a major problem with under-diagnosis.
There has been ongoing confusion as to whether LMBBS should be described instead as two distinct disorders: LMS and BBS. In the late 1800's, two physicians named John Z. Laurence and Robert Moon described four out of eight siblings who had retinitis pigmentosa, lack of intelligence, short stature, spastic paraparesis, and hypogenitalism in the males. In 1920, Dr. George Bardet submitted a thesis on hypothalamic obesity and noticed that a number of the cases examined had hexadactyly, retinitis pigmentosa, and obesity. Then, in 1922, Dr. Artur Biedel published an account of siblings with retinitis pigmentosa, polydactyly, and intellectual impairment. As a result, in 1925, it was decided that the conditions described by all of these physicians were the same and the disorder was named Laurence-Moon-Bardet-Biedl syndrome (LMBBS). Recently, however, the syndrome was split into Laurence-Moon (LMS) and Bardet-Biedl (BBS), where LMS is characterized as the cases involving mental retardation and spastic paresis and BBS involved obesity, polydactyly, and learning disabilities. It has been shown that BBS represents the majority of published cases.
Features and Characteristics
Following is a list of characteristics that have been seen in children with LMBBS. Not all children will exhibit all of these features:
Rod-cone dystrophy (retinitis pigmentosa)
Strabismus
Nystagmus
Myopia
Optic atrophy
Macular dystrophy
Glaucoma
Cataracts
Polydactyly (extra fingers and toes)
Brachydactyly (short, stubby fingers and toes)
Syndactyly (webbing of the toes)
Obesity (excess weight gain begins around ages 1 to 2 years)
Learning disabilities
Developmental delay (delay in sitting, standing, and walking)
Speech delay
Behavioral difficulties
Kidney abnormalities
Hepatic fibrosis
Hypertension (likely a consequence of obesity)
Diabetes mellitus
Hypothyroidism
Hypogonadism
Small penis
Undescended testes
Infertile males
Unusually short tooth roots
Short stature
Ataxic gaits
Deep-set eyes
Premature frontal balding in adult males
Diagnosis
It is often times very difficult to diagnose LMBBS. The diagnosis is first considered when a child is born with polydactyly. The diagnosis is usually made, however, when visual problems and obesity are noted. Following are the diagnostic criteria:
Primary Features (4 of these symptoms must be present for a diagnosis or 3 Primary and 2 Secondary, as shown below):
Rod-cone dystrophy
Polydactyly
Obesity
Learning disabilities
Hypogonadism in males
Renal anomalies
Secondary Features:
Speech disorder
Brachydactyly
Developmental delay
Polyuria/polydipsia
Ataxia
Poor coordination/clumsiness
Diabetes mellitus
Left ventricular hypertrophy
Hepatic fibrosis
Spasticity
For more info visit http://www.lmbbs.org.uk/