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Fragile X syndrome (FXS) is caused by an abnormal expansion of the number of trinucleotide CGG repeats located in the 5′ UTR in the first exon of the FMR1 gene. Size and methylation mosaicisms are commonly observed in FXS patients. Both types of mosaicisms might be associated with less severe phenotypes depending on the number of cells expressing FMRP. Although this dynamic mutation is the main underlying cause of FXS, other mechanisms, including point mutations or deletions, can lead to FXS. Several reports have demonstrated that de novo deletions including the entire or a portion of the FMR1 gene end up with the absence of FMRP and, thus, can lead to the typical clinical features of FXS. However, very little is known about the clinical manifestations associated with FMR1 gene deletions in mosaicism. Here, we report an FXS case caused by an entire hemizygous deletion of the FMR1 gene caused by maternal mosaicism. This manuscript reports this case and a literature review of the clinical manifestations presented by carriers of FMR1 gene deletions in mosaicism. [ABSTRACT FROM AUTHOR]

Lethal congenital contracture syndrome 11 (LCCS11) is caused by homozygous or compound heterozygous variants in the GLDN gene on chromosome 15q21. GLDN encodes gliomedin, a protein required for the formation of the nodes of Ranvier and development of the human peripheral nervous system. We report a fetus with ultrasound alterations detected at 28 weeks of gestation. The fetus exhibited hydrops, short long bones, fixed limb joints, absent fetal movements, and polyhydramnios. The pregnancy was terminated and postmortem studies confirmed the prenatal findings: distal arthrogryposis, fetal growth restriction, pulmonary hypoplasia, and retrognathia. The fetus had a normal chromosomal microarray analysis. Exome sequencing revealed two novel compound heterozygous variants in the GLDN associated with LCCS11. This manuscript reports this case and performs a literature review of all published LCCS11 cases. [ABSTRACT FROM AUTHOR]