Meckel syndrome

What it is, symptoms and effects

From: MedlinePlus Genetics, National Library of Medicine

Meckel syndrome is a disorder with severe signs and symptoms that affect many parts of the body. The most common features are enlarged kidneys with numerous fluid-filled cysts; an occipital encephalocele, which is a sac-like protrusion of the brain through an opening at the back of the skull; and the presence of extra fingers and toes (polydactyly). Most affected individuals also have a buildup of scar tissue (fibrosis) in the liver.

Other signs and symptoms of Meckel syndrome vary widely among affected individuals. Numerous abnormalities of the brain and spinal cord (central nervous system) have been reported in people with Meckel syndrome, including a group of birth defects known as neural tube defects. These defects occur when a structure called the neural tube, a layer of cells that ultimately develops into the brain and spinal cord, fails to close completely during the first few weeks of embryonic development. Meckel syndrome can also cause problems with development of the eyes and other facial features, heart, bones, urinary system, and genitalia.

Because of their serious health problems, most individuals with Meckel syndrome die before or shortly after birth. Most often, affected infants die of respiratory problems or kidney failure.

Causes and biological mechanisms

From: MedlinePlus Genetics, National Library of Medicine

Meckel syndrome can be caused by mutations in one of at least eight genes. The proteins produced from these genes are known or suspected to play roles in cell structures called cilia. Cilia are microscopic, finger-like projections that stick out from the surface of cells and are involved in signaling pathways that transmit information between cells. Cilia are important for the structure and function of many types of cells, including brain cells and certain cells in the kidneys and liver.

Mutations in the genes associated with Meckel syndrome lead to problems with the structure and function of cilia. Defects in these cell structures probably disrupt important chemical signaling pathways during early development. Although researchers believe that defective cilia are responsible for most of the features of this disorder, it remains unclear how they lead to specific developmental abnormalities of the brain, kidneys, and other parts of the body.

Mutations in the eight genes known to be associated with Meckel syndrome account for about 75 percent of all cases of the condition. In the remaining cases, the genetic cause is unknown. Mutations in several other genes have been identified in people with features similar to those of Meckel syndrome, although it is unclear whether these individuals actually have Meckel syndrome or a related disorder (often described as a "Meckel-like phenotype").

Inheritance and family implications

From: MedlinePlus Genetics, National Library of Medicine

This condition is inherited in an autosomal recessive pattern, which means both copies of the gene in each cell have mutations. The parents of an individual with an autosomal recessive condition each carry one copy of the mutated gene, but they typically do not show signs and symptoms of the condition.

How common is it?

From: MedlinePlus Genetics, National Library of Medicine

Meckel syndrome affects 1 in 13,250 to 1 in 140,000 people worldwide. It is more common in certain populations; for example, the condition affects about 1 in 9,000 people of Finnish ancestry and about 1 in 3,000 people of Belgian ancestry.

Reported clinical features and what the terms mean

The following findings are associated with this condition in Orphanet. They are not a checklist for diagnosing yourself, and they do not all occur in every affected person. Some are examination, imaging or laboratory findings that cannot be recognised at home.

The frequency labels describe how often a finding was reported among people with the condition in the source. They do not give the chance that a person with that symptom has the condition. Definitions below reproduce HPO terminology; they explain the term, not the likely severity in an individual.

Congenital hepatic fibrosis · Very frequent (99-80%)

The presence of fibrosis of that part of the liver with congenital onset.

Encephalocele · Very frequent (99-80%)

A neural tube defect characterized by sac-like protrusions of the brain and the membranes that cover it through openings in the skull.

Microcephaly · Very frequent (99-80%)

Head circumference below 2 standard deviations below the mean for age and gender.

Multicystic kidney dysplasia · Very frequent (99-80%)

Multicystic dysplasia of the kidney is characterized by multiple cysts of varying size in the kidney and the absence of a normal pelvicaliceal system. The condition is associated with ureteral or ureteropelvic atresia, and the affected kidney is nonfunctional.

Postaxial foot polydactyly · Very frequent (99-80%)

Polydactyly of the foot most commonly refers to the presence of six toes on one foot. Postaxial polydactyly affects the lateral ray and the duplication may range from a well-formed articulated digit to a rudimentary digit.

Postaxial hand polydactyly · Very frequent (99-80%)

Supernumerary digits located at the ulnar side of the hand (that is, on the side with the fifth finger).

Ambiguous genitalia · Frequent (79-30%)

A genital phenotype that is not clearly assignable to a single gender. Ambiguous genitalia can be evaluated using the Prader scale: Prader 0: Normal female external genitalia. Prader 1: Female external genitalia with clitoromegaly. Prader 2: Clitoromegaly with partial labial fusion forming a funnel-shaped urogenital sinus. Prader 3: Increased phallic enlargement. Complete labioscrotal fusion forming a urogenital sinus with a single opening. Prader 4: Complete scrotal fusion with urogenital opening at the base or on the shaft of the phallus. Prader 5: Normal male external genitalia. The diagnosis of ambiguous genitalia is made for Prader 1-4.

Aplasia/Hypoplasia of the iris · Frequent (79-30%)

Absence or underdevelopment of the iris.

Other findings in the same source

From: Orphanet

Additional reported features include Cataract (Frequent (79-30%)); Chorioretinal abnormality (Frequent (79-30%)); Cleft palate (Frequent (79-30%)); Cryptorchidism (Frequent (79-30%)); Depressed nasal ridge (Frequent (79-30%)); Full cheeks (Frequent (79-30%)); Hypertelorism (Frequent (79-30%)); Lobar holoprosencephaly (Frequent (79-30%)); Microcornea (Frequent (79-30%)); Micrognathia (Frequent (79-30%)). This is a selected summary, not a complete description of the condition.

Which doctor should you see?

The suggested department for discussing Meckel syndrome is Clinical Genetics, with a clinical geneticist as the relevant type of clinician. Paediatrician (children) or physician (adults), with clinical geneticist referral.

This is an editorial referral starting point. The appropriate clinic depends on the person’s age, symptoms, previous diagnosis and local services. The first clinician can decide whether another specialty or a team is needed; a department label does not confirm the diagnosis.

How to prepare for an assessment

Bring a short timeline of the main symptoms: when they first appeared, whether they are constant or episodic, what seems to change them, and how they affect daily activities. Include previous reports, discharge summaries, current medicines and supplements, allergies, and any relevant family history. A dated record is more useful than trying to match every feature in an online article.

Ask the clinician what is already established and what remains uncertain. If a test is suggested, ask what question it answers, what its limitations are and how the result would change the next step. The information here is not an instruction to arrange every possible test. In children, bring growth, developmental and school information if it is relevant to the concern.

• Does the exact genetic or chromosome finding explain the observed features?
• Would a genetic counsellor help the family understand the result?
• Which organ-specific assessments are appropriate for this particular diagnosis?

Treatment discussions and follow-up

The material gathered for this draft does not provide a complete condition-specific treatment pathway for Meckel syndrome. That gap does not mean that treatment is unavailable. A clinician needs to establish the diagnosis and review current guidance before recommending medicines, procedures, rehabilitation or other support.

Before leaving the appointment, clarify the next review date, who will communicate results, and whom to contact if the situation changes. Discuss difficulties with sleep, work, school, mobility, eating or emotional wellbeing when these are relevant. Practical support may require coordination between the treating clinician and other services.

The collected references do not establish a complete prevention or long-term outlook section for this entry. Missing information should not be interpreted as proof that prevention is impossible or that a particular outcome is inevitable. Ask what is known for the exact subtype, stage and personal circumstances, and which uncertainties remain.

When to seek emergency help

Severe breathing difficulty, collapse, new stroke-like symptoms, a seizure that is prolonged or repeated without recovery, uncontrolled major bleeding, or an immediate risk of self-harm require emergency help. In India, call 112 or reach the nearest emergency department. This is a general, non-exhaustive warning list; it is not a condition-specific triage tool.