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Abstract Mutations in sonic hedgehog ( SHH ; OMIM *600725) and the aristaless-related homeobox gene ( ARX ; OMIM *300382) can both result in severe brain malformation. Haploinsufficiency of SHH has been shown to cause not only midline structure defects such as holoprosencephaly, corpus callosum agenesis but also developmental delay and/or craniofacial dysmorphic features including microcephaly, hypotelorism, or a single central incisor. Mutations in the ARX gene may result in different phenotypes as well, such as X-linked mental retardation (XLMR; OMIM #300419), X-linked lissencephaly with ambiguous genitalia (XLAG; OMIM #300215), Partington syndrome (OMIM #309510), X-linked myoclonic epilepsy (OMIM #300432), X-linked West syndrome (OMIM #308350), and agenesis of the corpus callosum with abnormal genitalia (OMIM #300004). In a total number of 27 patients with complete or partial absence of the corpus callosum, SHH and ARX genes were investigated in order to evaluate whether mutations in SHH and ARX result in partial (dysgenesis) or complete (agenesis) absence of the corpus callosum. No causative mutations could be detected suggesting that these genes may not play a major role in corpus callosum formation.

Retinitis pigmentosa (RP) and Leber congenital amaurosis (LCA) are major causes of blindness. They result from mutations in many genes which has long hampered comprehensive genetic analysis. Recently, targeted next-generation sequencing (NGS) has proven useful to overcome this limitation. To uncover \"hidden mutations\" such as copy number variations (CNVs) and mutations in non-coding regions, we extended the use of NGS data by quantitative readout for the exons of 55 RP and LCA genes in 126 patients, and by including non-coding 5' exons. We detected several causative CNVs which were key to the diagnosis in hitherto unsolved constellations, e.g. hemizygous point mutations in consanguineous families, and CNVs complemented apparently monoallelic recessive alleles. Mutations of non-coding exon 1 of EYS revealed its contribution to disease. In view of the high carrier frequency for retinal disease gene mutations in the general population, we considered the overall variant load in each patient to assess if a mutation was causative or reflected accidental carriership in patients with mutations in several genes or with single recessive alleles. For example, truncating mutations in RP1, a gene implicated in both recessive and dominant RP, were causative in biallelic constellations, unrelated to disease when heterozygous on a biallelic mutation background of another gene, or even non-pathogenic if close to the C-terminus. Patients with mutations in several loci were common, but without evidence for di- or oligogenic inheritance. Although the number of targeted genes was low compared to previous studies, the mutation detection rate was highest (70%) which likely results from completeness and depth of coverage, and quantitative data analysis. CNV analysis should routinely be applied in targeted NGS, and mutations in non-coding exons give reason to systematically include 5'-UTRs in disease gene or exome panels. Consideration of all variants is indispensable because even truncating mutations may be misleading.

Schizencephaly (SCH) is a clinically and etiologically heterogeneous cerebral malformation presenting as unilateral or bilateral hemispheric cleft with direct connection between the inner and outer liquor spaces. The SCH cleft is usually lined by gray matter, which appears polymicrogyric implying an associated impairment of neuronal migration. The majority of SCH patients are sporadic, but familial SCH has been described. An initial report of heterozygous mutations in the homeobox gene EMX2 could not be confirmed in 52 patients investigated in this study in agreement with two independent SCH patient cohorts published previously. SCH frequently occurs with additional cerebral malformations like hypoplasia or aplasia of the septum pellucidum or optic nerve, suggesting the involvement of genes important for the establishment of midline forebrain structures. We therefore considered holoprosencephaly (HPE)-associated genes as potential SCH candidates and report for the first time heterozygous mutations in SIX3 and SHH in a total of three unrelated patients and one fetus with SCH; one of them without obvious associated malformations of midline forebrain structures. Three of these mutations have previously been reported in independent patients with HPE. SIX3 acts directly upstream of SHH, and the SHH pathway is a key regulator of ventral forebrain patterning. Our data indicate that in a subset of patients SCH may develop as one aspect of a more complex malformation of the ventral forebrain, directly result from mutations in the SHH pathway and hence be considered as yet another feature of the broad phenotypic spectrum of holoprosencephaly.

Interstitial deletions or apparently balanced translocations involving bands 1p31 and 1p32 in the short arm of chromosome 1 are rarely described chromosomal imbalances. To our knowledge, there have been six cases documented to date. Five of these cases, where the NFIA gene is involved, show complex central nervous system malformations and in some cases urinary tract defects. We report another case of a microdeletion with involvement of the NFIA gene in the short arm of chromosome 1 (del(1)(p31.3p32.2)) with, amongst other features, hypoplasia of the corpus callosum, ventriculomegaly, and dysmorphic features. A microdeletion 1p31.3p32.2 which includes the NFIA gene is associated with hypoplasia of the corpus callosum, ventriculomegaly, and dysmorphic features.

Gomez-Lopez-Hernandez syndrome is a very rare genetic disorder with a distinct phenotype (OMIM 601853). To our knowledge there have been seven cases documented to date. We report on an additional male patient now aged 15 8/12 years with synostosis of the lambdoid suture, partial scalp alopecia, corneal opacity, mental retardation and striking phenotypic features (e.g., brachyturricephaly, hypertelorism, midface hypoplasia and low-set ears) consistent with Gomez-Lopez-Hernandez syndrome. In early childhood the patient demonstrated aggressive behavior and raging periods. He also had seizures that were adequately controlled by medication. Magnetic resonance imaging (MRI) revealed rhombencephalosynapsis, i.e., a rare fusion of the cerebellar hemispheres, also consistent with Gomez-Lopez-Hernandez syndrome. In addition a lipoma of the quadrigeminal plate was observed, a feature not previously described in the seven patients reported in the literature. Cytogenetic and subtelomere analyses were inconspicuous. Microarray-based comparative genomic hybridization (array-CGH) testing revealed five aberrations (partial deletions of 1p21.1, 8q24.23, 10q11.2, Xq26.3 and partial duplication of 19p13.2), which, however, have been classified as normal variants. Array-CGH has not been published in the previously reported children. The combination of certain craniofacial features, including partial alopecia, and the presence of rhombencephalosynapsis in the MRI are suggestive of Gomez-Lopez-Hernandez syndrome. Children with this syndrome should undergo a certain social pediatric protocol including EEG diagnostics, ophthalmological investingation, psychological testing, management of behavioral problems and genetic counseling.

Alopecia–contractures–dwarfism mental retardation syndrome (ACD syndrome; OMIM 203550) is a very rare genetic disorder with distinct features. To our knowledge, there have been four cases documented to date. In addition, another three patients, previously described as having IFAP syndrome (OMIM %308205), may also have ACD syndrome. We report on one patient with short stature, total alopecia, ichthyosis, photophobia, seizures, ectrodactyly, vertebral anomalies, scoliosis, multiple contractures, mental retardation, and striking facial and other features (e.g. microdolichocephaly, missing eyebrows and eyelashes, long nose, large ears) consistent with ACD syndrome. Results of laboratory testing in the literature case reports were normal, although in none of them, array-CGH (microarray-based comparative genomic hybridization) analysis was performed. In conclusion, the combination of specific features, including total alopecia, ichthyosis, mental retardation, and skeletal anomalies are suggestive of ACD syndrome. We propose that children with this syndrome undergo a certain social pediatric protocol including EEG diagnostics, ophthalmological investigation, psychological testing, management of dermatologic and orthopedic problems, and genetic counseling.