Earliest ultrasound findings and description of splicing mutations in Meckel-Gruber syndrome
ABSTRACT To describe early ultrasound findings in Meckel-Gruber syndrome (MKS) in first and second trimester of three families, detailed ultrasound findings have been documented in addition to pathoanatomical findings and results of DNA studies. A splice site mutation in the MKS4 gene could be detected. Clinical management accounting risk assessment for future pregnancies is discussed and early ultrasound markers in MKS are described.
All cases were examined in a tertiary center for prenatal diagnosis by ultrasound. Necroscopy confirmed the clinical diagnosis. Fetal DNA analysis was accomplished in a reference center for MKS. In addition, ultrasound findings in early pregnancy of two further cases are described.
Three couples presented with pregnancies complicated by MKS. The earliest diagnosis was suspected in 11 + 6 weeks of gestation and was confirmed in 13 + 0 weeks by ultrasound revealing a large occipital encephalocele and polycystic kidneys. Another case with recurrent MKS in two consecutive pregnancies was diagnosed in 20 weeks and 14 weeks of gestation, respectively. Here a close molecular genetic follow-up was performed leading to the detection of two mutations in the MKS4 gene in both fetuses. The third case was diagnosed in 15 weeks of gestation. Ultrasound findings in all pregnancies were doubtless and autopsies confirmed the diagnosis.
Detection of MKS is already possible in the first trimester. Knowledge of the underlying genetic defect helps counseling the couples with recurrence of MKS and chorionic villi sampling in the first trimester of pregnancy can be offered.
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ABSTRACT: Joubert (JBTS) and Meckel-Gruber (MKS) syndromes are recessive neurodevelopmental conditions caused by mutations in proteins that are structural or functional components of the primary cilium. In this review we provide an overview of their clinical diagnosis, management and molecular genetics. Both have variable phenotypes, extreme genetic heterogeneity, and display allelism both with each other and other ciliopathies. Recent advances in genetic technology have significantly improved diagnosis and clinical management of ciliopathy patients, with the delineation of some general genotype-phenotype correlations. We highlight those that are most relevant for clinical practice, including the correlation between TMEM67 mutations and the JBTS variant phenotype of COACH syndrome. The subcellular localization of the known MKS and JBTS proteins is now well-described, and we discuss some of the contemporary ideas about ciliopathy disease pathogenesis. Most JBTS and MKS proteins localize to a discrete ciliary compartment called the transition zone (TZ), and act as structural components of the so-called "ciliary gate" to regulate the ciliary trafficking of cargo proteins or lipids. Cargo proteins include enzymes and transmembrane proteins that mediate intracellular signaling. The disruption of TZ function may contribute to the ciliopathy phenotype by altering the composition of the ciliary membrane or axoneme, with impacts on essential developmental signaling including the Wnt and Shh pathways as well as the regulation of secondary messengers such as inositol-1,4,5-trisphosphate (InsP3) and cAMP. However, challenges remain in the interpretation of the pathogenic potential of genetic variants of unknown significance, and in the elucidation of the molecular mechanisms of phenotypic variability in JBTS and MKS. The further genetic and functional characterization of these conditions is essential to prioritize patients for new targeted therapies.
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ABSTRACT: We describe a first trimester ultrasound in which the findings of fetal encephalocele and cystic appearance of the kidneys raised the suspicion of Meckel-Gruber Syndrome (MKS). On the basis of the sonographic findings, the patient elected termination of pregnancy, and post-termination studies using next generation sequencing of a gene panel revealed two mutations (one previously described and the other novel) in the gene CC2D2A. Mutations in CC2D2A are known to cause Meckel-Gruber and Joubert Syndromes, thus providing molecular confirmation of the clinical suspicion of MKS and opening the possibility for future prenatal diagnosis. This case highlights the ability of ultrasound to detect important anomalies in the first trimester, even in low risk situations. It also demonstrates the growing role of new sequencing technologies in fetal testing.Ultrasound in Obstetrics and Gynecology 12/2014; 44(6). DOI:10.1002/uog.13381