Mutations in CHD7 are the major cause of CHARGE syndrome, an autosomal dominant disorder with an estimated prevalence of 1/15,000. We have little understanding of the disruptions in the developmental programme that underpin brain defects associated with this syndrome. Using mouse models, we show that Chd7 haploinsufficiency results in reduced Fgf8 expression in the isthmus organiser (IsO), an embryonic signalling centre that directs early cerebellar development. Consistent with this observation, Chd7 and Fgf8 loss-of-function alleles interact during cerebellar development. CHD7 associates with Otx2 and Gbx2 regulatory elements and altered expression of these homeobox genes implicates CHD7 in the maintenance of cerebellar identity during embryogenesis. Finally, we report cerebellar vermis hypoplasia in 35% of CHARGE syndrome patients with a proven CHD7 mutation. These observations provide key insights into the molecular aetiology of cerebellar defects in CHARGE syndrome and link reduced FGF signalling to cerebellar vermis hypoplasia in a human syndrome.DOI: http://dx.doi.org/10.7554/eLife.01305.001

The R6/2 mouse model of Huntington’s disease exhibits reduced skeletal muscle ClC-1 currents. Miranda et al. investigate early stages of disease in these mice and find an early and progressive disruption of ClC-1 as well as altered muscle maturation based on myosin heavy chain isoform expression.

CHARGE syndrome is caused by a dominant variant in the CHD7 gene. Multiple organ systems can be affected because of haploinsufficiency of CHD7 during embryonic development. CHARGE syndrome shares many clinical features with the 22q11.2 deletion syndrome. Immunological abnormalities have been described, but are generally given little attention in studies on CHARGE syndrome. However, structured information on immunological abnormalities in CHARGE patients is necessary to develop optimal guidelines for diagnosis, treatment and follow-up in these patients. Here, we provide an overview of the current literature on immunological abnormalities in CHARGE syndrome. We also explore immunological abnormalities in comparable multiple congenital anomaly syndromes to identify common immunological phenotypes and genetic pathways that might regulate the immune system. Finally, we aim to identify gaps in our knowledge on the immunological aspects in CHARGE syndrome that need further study.

CHARGE syndrome is a variable, multiple congenital malformation syndrome. Patients with CHARGE syndrome have frequent infections that are presumed to be due to anatomical anomalies of the craniofacial region and upper airway, and cranial nerve problems resulting in swallowing difficulties and aspiration. The possible contribution of immunological abnormalities to these infections has not been systematically studied even though immune deficiencies have been described in patients with 22q11.2 deletion syndrome, a condition which shares remarkable clinical overlap with CHARGE syndrome. We assessed the frequency and nature of immune dysfunction in 24 children with genetically proven CHARGE syndrome. All patients, or their parents, completed a questionnaire on infectious history. Their immune system was extensively assessed through full blood counts, immunoglobulin levels, lymphocyte subpopulations, peripheral B- and T-cell differentiation, T-receptor excision circle (TREC) analysis, T-cell function, and vaccination responses. All CHARGE patients had a history of infections (often frequent), mainly otitis media and pneumonia, leading to frequent use of antibiotics and to hospital admissions. Decreased T-cell numbers were found in 12 (50%) patients, presumably caused by insufficient thymic output since TREC amounts were also diminished in CHARGE patients. Despite normal peripheral B-cell differentiation and immunoglobulin production in all patients, 83% of patients had insufficient antibody titers to one or more early childhood vaccinations. Based on our results, we recommend immunological evaluation of CHARGE patients with recurrent infections.

CHARGE syndrome is an autosomal dominant malformation disorder caused by heterozygous loss of function mutations in the chromatin remodeler CHD7. Chd7 regulates the expression of Sema3a, which also contributes to the pathogenesis of Kallmann syndrome, a heterogeneous condition with the typical features hypogonadotropic hypogonadism and an impaired sense of smell. Both features are common in CHARGE syndrome suggesting that SEMA3A may provide a genetic link between these syndromes. Indeed, we find evidence that SEMA3A plays a role in the pathogenesis of CHARGE syndrome. First, Chd7 is enriched at the Sema3a promotor in neural crest cells and loss of function of Chd7 inhibits Sema3a expression. Second, using a Xenopus CHARGE model, we show that human SEMA3A rescues Chd7 loss of function. Third, to elucidate if SEMA3A mutations in addition to CHD7 mutations also contribute to the severity of the CHARGE phenotype, we screened 31 CHD7-positive patients and identified one patient with a heterozygous non-synonymous SEMA3A variant, c.2002A>G (p.I668V). By analyzing protein expression and processing, we did not observe any differences of the p.I668V variant compared with wild-type SEMA3A, while a pathogenic SEMA3A variant p.R66W recently described in a patient with Kallmann syndrome did affect protein secretion. Furthermore, the p.I668V variant, but not the pathogenic p.R66W variant, rescues Chd7 loss of function in Xenopus, indicating that the p.I668V variant is likely benign. Thus, SEMA3A is part of an epigenetic loop that plays a role in the pathogenesis of CHARGE syndrome, however, it seems not to act as a common direct modifier.

CHD7 variants are a well-established cause of CHARGE syndrome, a disabling multi-system malformation disorder that is often associated with deafness, visual impairment and intellectual disability. Less severe forms of CHD7-related disease are known to exist, but the full spectrum of phenotypes remains uncertain. We identified a de novo missense variant in CHD7 in a family presenting with musculoskeletal abnormalities as the main manifestation of CHD7-related disease, representing a new phenotype. The proband presented with prominent scapulae, mild shoulder girdle weakness and only subtle dysmorphic features. Investigation revealed hypoplasia of the trapezius and sternocleidomastoid muscles and semicircular canal defects, but he did not fulfill diagnostic criteria for CHARGE syndrome. Although the shoulders are often sloping and anteverted in CHARGE syndrome, the underlying neuromuscular cause has never been investigated. This report expands the phenotypes associated with CHD7 mutations to include a musculoskeletal presentation, with hypoplasia of the shoulder and neck muscles. CHD7 should be considered in patients presenting in childhood with stable scapular winging, particularly if accompanied by dysmorphic features and balance difficulties.

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