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Laurence-Moon-Biedl-Bardet syndrome

Laurence-Moon-Biedl-Bardet syndrome



Overview

Laurence-Moon-Bardet-Biedl syndrome (LMBBS) is a rare genetic disorder, though some now consider it a distinct condition from Bardet-Biedl syndrome (BBS) due to different genetic causes. It is characterized by a combination of symptoms including early-onset vision loss due to retinitis pigmentosa, central obesity, post-axial polydactyly (extra fingers or toes), mental retardation, and hypogonadism (underdeveloped sex organs). It is a ciliopathy, meaning it affects a cellular structure called the cilium, and can also involve kidney dysfunction, developmental delays, and other issues

Symptoms

Vision: Early night blindness, loss of peripheral vision, leading to legal blindness.

Physical: Extra fingers or toes (polydactyly), central obesity, poor coordination, distinctive facial features, dental issues, short stature.

Neurological/Cognitive: Intellectual disability, learning difficulties, speech delays, behavioral issues (like anxiety, anger).

Endocrine/Reproductive: Hypogonadism (underdeveloped sex organs), infertility, sometimes diabetes.

Renal: Structural or functional kidney abnormalities, chronic kidney disease. 

Causes

Autosomal Recessive Inheritance: LMBBS is passed down in families as an autosomal recessive trait, meaning a child must inherit a mutated gene from both parents to develop the syndrome, although parents often show no symptoms.

Ciliopathy: It's classified as a "ciliopathy," affecting cilia, which are essential for many bodily functions, explaining the diverse symptoms.

Gene Mutations: Mutations in over a dozen genes (like BBS1, BBS2, BBS4, BBS7, PNPLA6) are known to cause LMBBS, all affecting cilia structure or function. 

Diagnosis

Clinical Suspicion: Often raised in childhood due to early vision loss (night blindness, tunnel vision) or polydactyly, especially in families with consanguinity.

Multisystem Evaluation: Doctors look for the combination of primary/secondary signs, including eye exams (fundus copy), hormone levels, kidney function tests, and neurodevelopmental assessment.

Genetic Testing: Essential for confirmation, typically using multigene panels (like whole exome sequencing or panels targeting BBS genes) to find pathogenic variants in genes like BBS1-18.

Differentiation: Genetic testing helps distinguish LMBBS from Laurence-Moon Syndrome (LMS), now linked specifically to the PNPLA6 gene. 

Treatment

Obesity & Hyperphagia:

Setmelanotide (Imcivree): FDA/EMA-approved for genetic obesity in BBS.

Diet & Lifestyle: Low-protein diets (for kidneys), dietitian, behavioral therapy, exercise.

Emerging: GLP-1 agonists show promise in mouse models.

Vision Loss (Retinal Dystrophy):

No cure, but glasses help, and low-vision specialists provide support.

Gene therapies are in development.

Kidney Dysfunction:

Intensive management, often a low-protein diet to slow progression, monitoring for failure.

Endocrine Issues (Hypogonadism, Short Stature):

Hormone replacement (levothyroxine for metabolism, testosterone for hypogonadism, growth hormone).

Polydactyly (Extra Digits):

Surgical removal for cosmetic and functional reasons, often done in childhood.

Developmental/Psychological:

Early educational support, speech/physical therapy, psychological counseling for patients and families.

Gallstones:

Surgical removal (laparoscopic cholecystectomy) if symptomatic, otherwise expectant management. 

Type of Doctor Department : APediatrician, Ophthalmologists (vision), Nephrologists (kidneys), Endocrinologists (hormones/obesity), Geneticists, and possibly Rehabilitation specialists


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