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Rhombencephalosynapsis (RES) is a rare congenital anomaly of the hindbrain characterized by fusion of the cerebellar hemispheres, cerebellar peduncles, and dentate nuclei with vermian absence or hypogenesis. This anomaly can be isolated or part of a larger spectrum of cerebral abnormalities. At least 90 cases are described in the literature and it has been associated with VACTERL and Gomez-Lopez-Hernandez syndrome (GLHS). The most common congenital syndrome associated with RES is GLHS, a rare presumed genetic disorder with over 30 cases thus far described in the literature. No genetic cause has been identified for RES or GLHS. We report two probands diagnosed with GLHS based on clinical criteria. Each proband had RES and bi-parietal scalp alopecia as well as neurologic findings and phenotypic features including trigeminal anesthesia, borderline hypertelorism, midface retrusion, and motor delay. Oliginucleotide-SNP microarray on the male proband revealed a 1.05 Mb copy duplication of uncertain clinical significance at 15q21.3 while oligonucleotide-SNP microarray for the female proband did not reveal any abnormalities. Exome sequencing (ES) was performed on both patients and did not identify any variants that could explain the GLHS phenotype. To our knowledge, these are the first two patients with GLHS described in the literature to undergo ES. Both patients had mild neurologic manifestations requiring physical therapy in early life without known diagnostic cause. Patients found to have scalp alopecia or trigeminal anesthesia with gross motor delay should be evaluated for RES or GLHS as well as screened for associated syndromes and have a complete neurodevelopmental evaluation., (© 2020 Wiley Periodicals, Inc.)

Rhombencephalosynapsis (RES) is a unique cerebellar malformation characterized by fusion of the cerebellar hemispheres with partial or complete absence of a recognizable cerebellar vermis. Subsets of patients also have other brain malformations such as midbrain fusion with aqueductal stenosis, characteristic craniofacial features (prominent forehead, flat midface, hypertelorism, ear abnormalities), and somatic malformations (heart, kidney, spine, and limb defects). Similar to known genetic brain malformations, the RES cerebellar malformation is highly stereotyped, yet no genetic causes have been identified. Here, we outline our current understanding of the genetic basis for RES, discuss limitations, and outline future approaches to identifying the causes of this fascinating brain malformation., (© 2018 Wiley Periodicals, Inc.)

Joubert syndrome (JS) is a rare, recessively inherited neurodevelopmental disorder characterized by a distinctive mid-hindbrain malformation. Little is known about mortality in affected individuals. Identifying the timing and causes of death will allow for development of healthcare guidelines for families and providers and, thus, help to prolong and improve the lives of patients with JS. We evaluated information on 40 deceased individuals with JS to characterize age and cause of death. We compared this population with 525 living individuals with JS to estimate associations between risk of death and extra-neurological features. Genetic causes were examined in both groups. Mean age of death in this cohort was 7.2 years, and the most prevalent causes of death were respiratory failure (35%), particularly in individuals younger than 6 years, and kidney failure (37.5%), which was more common in older individuals. We identified possible associations between risk of death and kidney disease, liver fibrosis, polydactyly, occipital encephalocele, and genetic cause. This work highlights factors (genetic cause, extra-neurological organ involvement, and other malformations) likely to be associated with higher risk of mortality in JS, which should prompt increased monitoring for respiratory issues, kidney disease, and liver fibrosis., (© 2017 Wiley Periodicals, Inc.)

Rhombencephalosynapsis (RES) is a rare hindbrain malformation that could occur in isolation or as a part of a syndrome for example, Gómez-López-Hernández syndrome (GLH) or VACTERL-H. We identified male patient with severe RES. Ventriculomegaly, agenesis of septum pellucidum, very thin corpus callosum with interhemispheric cyst were additional neuroimaging findings. He had brachyturricephaly, midface retrusion, low-set posteriorly rotated ears and bilateral parietal well circumscribed areas of alopecia. No corneal anesthesia was observed; thus, demonstrating many of the diagnostic criteria of GLH. Interestingly, he additionally had bilateral bipartite parietal bone (BPB) that is an extremely rare anomaly of the parietal sutures. This is the first co-occurrence of this rare anomaly with GLH. We believe the presence of this unique finding could represent an important clue for understanding the pathogenesis of this malformation., (© 2013 Wiley Periodicals, Inc.)

Rhombencephalosynapsis (RES) is an uncommon cerebellar malformation characterized by fusion of the hemispheres without an intervening vermis. Frequently described in association with Gómez-López-Hernández syndrome, RES also occurs in conjunction with VACTERL features and with holoprosencephaly (HPE). We sought to determine the full phenotypic spectrum of RES in a large cohort of patients. Information was obtained through database review, patient questionnaire, radiographic, and morphologic assessment, and statistical analysis. We assessed 53 patients. Thirty-three had alopecia, 3 had trigeminal anesthesia, 14 had VACTERL features, and 2 had HPE with aventriculy. Specific craniofacial features were seen throughout the cohort, but were more common in patients with alopecia. We noted substantial overlap between groups. We conclude that although some distinct subgroups can be delineated, the overlapping features seen in our cohort suggest an underlying spectrum of RES-associated malformations rather than a collection of discrete syndromes., (Copyright © 2012 Wiley Periodicals, Inc.)

Rhombencephalosynapsis (RES) is a rare congenital brain malformation typically identified by magnetic resonance imaging and characterized by fusion of the cerebellar hemispheres and dentate nuclei and vermian agenesis or hypogenesis. Although RES is frequently found in conjunction with other brain malformations and/or congenital anomalies, no specific molecular etiology has been discovered to date and no animal models exist. We identified two half sisters with alobar or semi-lobar holoprosencephaly (HPE) and partial RES, suggesting that genes linked to HPE may also contribute to RES. A deletion of seven base pairs in exon one of the ZIC2 gene (c.392_98del7) was identified in each of the two half sisters with HPE and partial RES. To identify genetic causes of RES and to assess whether genes identified in HPE have a role in RES, we tested 11 additional individuals with RES by high-resolution chromosome analysis, chromosomal microarray analysis, and sequencing of four HPE genes. No mutations in ZIC2 or in other genes that cause HPE were identified, suggesting that mutation of ZIC2 is a rare cause of, or contributor to, RES associated with HPE. In addition, an individual with a complex rearrangement of chromosome 22q13.3 and RES was identified, suggesting the presence of a dosage-sensitive gene that may contribute to RES in this region., (Copyright © 2011 Wiley-Liss, Inc.)

We review 25 patients with a spectrum of hindbrain (cerebellum, pons, and medulla) malformations from a cohort of children with high parental consanguinity rate. Twenty-three of the 25 patients were born to consanguineous parents. The patients were classified in four groups. Eleven patients of 6 families had malformation of the hindbrain and midbrain with molar tooth sign (10 patients of 5 families with typical Joubert syndrome), 5 patients showed severe supratentorial anomalies in addition to the hindbrain malformations, 5 patients had pontocerebellar or cerebellar hypoplasia with anterior horn cell disease in the spinal cord (spinal muscular atrophy), and 4 patients showed malformations affecting predominantly the hindbrain without substantial involvement of other systems. A locus for Joubert syndrome was previously identified on chromosome 9q34.3 in two families, and a second locus on chromosome 11p12-q13.3 in another family. A third Joubert syndrome locus has been mapped at 6q23 and a mutation in the AHI1 gene at this site has been found recently in a further family from this cohort. Delineation of homogeneous subgroups of patients with hindbrain malformations and molecular genetic analysis of these groups may lead to identification of further loci, genes and mutations responsible for the malformations., (Copyright (c) 2005 Wiley-Liss, Inc.)

Defining and classifying congenital disorders of the cerebellum can be difficult and confusing. One reason is that some abnormalities called "malformations" are not truly (primary) developmental malformations. This applies to Chiari I "malformations" as well as to Chiari II "malformations." The latter results mainly from a prenatal cerebrospinal fluid (CSF) leak. Also disruptive cerebellar lesions are not uncommon, examples being the "vanishing cerebellum" in myelomeningocele, cerebellar lesions in very low birth weight prematurely born infants, unilateral cerebellar hypoplasia/aplasia, and probably some instances of cerebellar agenesis (CA). The cerebellar hypoplasias consist of a heterogeneous group of inherited and prenatally acquired conditions. The concept of pontocerebellar hypoplasias will need to be expanded beyond the two main types (PCH-1 and PCH-2), and demonstrate that a classification system of cerebellar malformations cannot be based on neuroimaging criteria only. Additional studies are expected to show that this also applies to the molar tooth sign, which was initially described in Joubert syndrome (JS). The JS is the prototype of midhindbrain malformation, but its delineation is still unsolved. JS may well be an overdiagnosed entity; many cases likely not having JS are on record. Rhombencephalosynapsis (RS) has been increasingly diagnosed with the advent of neuroimaging. No familial cases have been observed. Although many affected individuals have variable impairments, RS can be found in children with normal cognitive function. In this review, some of the cerebellar anomalies are briefly discussed., (Copyright 2004 Wiley-Liss, Inc.)

During embryonic development, restricted expression of the regulatory genes Krox20 and kreisler are involved in segmentation and antero-posterior patterning of the hindbrain neural tube. The analysis of transgenic mice in which specific rhombomeres (r) are eliminated points to an important role of segmentation in the generation of neuronal networks controlling vital rhythmic behaviours such as respiration. Thus, elimination of r3 and r5 in Krox20-/- mice suppresses a pontine antiapneic system (Jacquin et al., 1996). We now compare Krox20-/- to kreisler heterozygous (+/kr) and homozygous (kr/kr) mutant neonates. In +/kr mutant mice, we describe hyperactivity of the antiapneic system: analysis of rhythm generation in vitro revealed a pontine modification in keeping with abnormal cell specifications previously reported in r3 (Manzanares et al., 1999b). In kr/kr mice, elimination of r5 abolished all +/kr respiratory traits, suggesting that +/kr hyperactivity of the antiapneic system is mediated through r5-derived territories. Furthermore, collateral chemosensory pathways that normally mediate delayed responses to hypoxia and hyperoxia were not functional in kr/kr mice. We conclude that the pontine antiapneic system originates from r3r4, but not r5. A different rhythm-promoting system originates in r5 and kreisler controls the development of antiapneic and chemosensory signal transmission at this level.

We report on a patient with bulbar-onset, clinically defined, sporadic amyotrophic lateral sclerosis (ALS) who also showed a Chiari I malformation. This malformation, otherwise asymptomatic, was detected during the diagnostic work-up for ALS. To our knowledge this is the first report of an association between these two relatively uncommon disorders. Since our patient worked for many years as a bus-driver and because the ALS symptoms began in the brainstem region, we suggest that his hindbrain anomaly, along with the mechanical stress on the spine and cranio-vertebral junction due to the daily driving, might have played a role in the region-specific onset of ALS.