Meckel-Gruber Syndrome

Updated: Jun 12, 2019
  • Author: Parul Bhagwati Jayakar, MD, MS, FACMG; Chief Editor: Luis O Rohena, MD, FAAP, FACMG  more...
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Overview

Practice Essentials

Meckel-Gruber syndrome (MKS) is a lethal, rare, autosomal recessive condition characterized by the triad of occipital encephalocele, large polycystic kidneys, and postaxial polydactyly. Associated abnormalities include oral clefting; genital anomalies; central nervous system (CNS) malformations, including Dandy-Walker and Arnold-Chiari malformation; and liver fibrosis. Pulmonary hypoplasia is the leading cause of death. Improvements in ultrasonography have enabled prenatal diagnosis as early as 10 weeks' gestation. [1]

The first reports of Meckel-Gruber syndrome were published in 1822 by Johann Friedrich Meckel. G.B. Gruber also published reports of patients with Meckel-Gruber syndrome in 1934 and gave it the name dysencephalia splanchnocystica. Meckel-Gruber syndrome is also known as either Meckel syndrome or Gruber syndrome.

The condition (OMIM 24900) has been mapped to 12 different loci in chromosomes 17q21-24 (MKS1), 11q13 (MKS2), 8q21.3-q22.1 (MKS3), [2, 3] 12q21.31-q21.33 (MKS4), [4] 16q12.2 (MKS5), [5] 4p15.3 (MKS6), [6] 3q22.1 (MKS7), [7] 12q24.31 (MKS8), [8] 17p11.2 (MKS9), [9] 19q13.2 (MKS10), [10] 16q23.1 (MKS11), [11] and 1q32.1 (MKS12). [12] This mapping suggests genetic heterogeneity in Meckel-Gruber syndrome.

A study by Barisic et al, using data from 191 cases of Meckel-Gruber syndrome, as accessed through the European Surveillance of Congenital Anomalies (EUROCAT) network, found the prevalence of various characteristics of the disease to be as follows [13] :

  • Cystic kidneys (97.7%)
  • Polydactyly (87.3%)
  • Encephalocele (83.8%)
  • Fibrotic/cystic changes of the liver (65.5%, as identified via postmortem examination)
  • Other CNS anomalies (51.4%)
  • Orofacial clefts (31.8%)

Workup

Prenatal ultrasonography is currently the best method available to diagnose Meckel-Gruber syndrome and is available in 2-dimensional (2D), 3-dimensional (3D), and 4-dimensional (4D) modalities.

Magnetic resonance imaging (MRI) is a valuable complement to ultrasonography in assessing fetal anomalies in the presence of severe oligohydramnios. It is mainly used when ultrasonography findings are inconclusive or are insufficient to guide treatment choices.

Chromosome analysis is essential to exclude trisomy 13, which Meckel-Gruber syndrome mimics.

If anomalies are detected early in the first trimester, chorionic villus sampling (CVS) can be performed at 10-12 weeks' gestation or later in pregnancy if oligohydramnios does not permit amniocentesis. Amniocentesis is performed after 14 weeks’ gestation if an adequate fluid pocket is present.

Management

Cardiac repair or neurosurgical intervention for encephalocele may be warranted in patients with Meckel-Gruber syndrome.

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Pathophysiology

Failure of mesodermal induction has been suggested to cause Meckel-Gruber syndrome. The induction cascades of early morphogenesis involve numerous growth factors, homeobox genes, and paired domain genes.

One study screened patients with Meckel syndrome for mutations in B9D1 and B9D2 and identified homozygous c.301A>C (p.Ser101Arg) B9D2 mutation. The data showed that the domain-containing proteins Mks1, B9d1, and B9d2 interact physically; the p.Ser101Arg mutation abrogates the ability of B9d2 to interact with Mks1, which suggests that this mutation compromised B9d2 function. The data further show that B9d1 is required for normal Hedgehog (Hh) signaling, ciliogenesis, and ciliary protein localization. [14] B9d1 and B9d2 are essential components of a B9 protein complex and, when this is disrupted, Meckel syndrome results. [15]

With tectonic family member 2 (Tctn2) protein mutation also being linked to Meckel-Gruber syndrome, a study by Weng et al using a knockout human retinal pigment epithelial cell line reported an association between Tctn2 depletion and the following [16] :

  • Partial damage to the ciliary transition zone, a diffusion barrier involved in the regulation of both ciliogenesis and receptor localization for key signaling events
  • Ciliary membrane protein loss
  • Leakage of intraflagellar transport 88 (Ift88) protein toward the lumen of the ciliary basal body
  • Shortening and curving of the cilium
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Epidemiology

Frequency

International

Worldwide, the incidence of Meckel-Gruber syndrome is 1 per 13,250-140,000 live births. Individuals of Finnish descent have a higher incidence (1 per 9000 live births, one person in 50 is a carrier). The incidence is also higher among Belgians and Bedouins in Kuwait, with 1 affected birth in 3,500 (carrier rate 1 in 30). The highest incidence is reported in the Gujarati Indians, with 1 affected birth per 1300 (carrier rate, 1 in 18). [17, 18] The incidence among Jews in Israel is 1 in 50,000 (carrier rate, 1 in 112). Cases of Meckel-Gruber syndrome have been reported in North America, Europe, Israel, Indonesia, India, Kuwait, and Japan.

Mortality/Morbidity

Oligohydramnios that results from dysplastic kidneys leads to fetal pulmonary hypoplasia. Because the prognosis is grim, with death occurring in utero or shortly after birth, prenatal diagnosis has led to therapeutic abortion of many affected fetuses. The mortality rate is 100%, with most fetuses surviving only a few days to weeks.

A study by Al-Belushi et al determined that among the report’s cases of prenatally discovered Meckel-Gruber syndrome, diagnostic results revealing no obvious polycystic kidney disease or severe oligohydramnios were consistent with live birth. However, 100% mortality occurred in the live-born infants within a few weeks postdelivery. [19]

Race

Although individuals of Finnish descent have the highest birth incidence, Meckel-Gruber syndrome affects all racial and ethnic backgrounds.

Sex

The male-to-female ratio is nearly equal, which is consistent with autosomal recessive inheritance.

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