A newly recognized autosomal recessive syndrome affecting neurologic function and vision

The genetic landscape of autism spectrum disorder in the Middle Eastern population

Introduction: Autism spectrum disorder (ASD) is characterized by aberrations in social interaction and communication associated with repetitive behaviors and interests, with strong clinical heterogeneity. Genetic factors play an important role in ASD, but about 75% of ASD cases have an undetermined genetic risk. Methods: We extensively investigated an ASD cohort made of 102 families from the Middle Eastern population of Qatar. First, we investigated the copy number variations (CNV) contribution using genome-wide SNP arrays. Next, we employed Next Generation Sequencing (NGS) to identify de novo or inherited variants contributing to the ASD etiology and its associated comorbid conditions in families with complete trios (affected child and the parents). Results: Our analysis revealed 16 CNV regions located in genomic regions implicated in ASD. The analysis of the 88 ASD cases identified 41 genes in 39 ASD subjects with de novo (n = 24) or inherited variants (n = 22). We identified three novel de novo variants in new candidate genes for ASD (DTX4, ARMC6, and B3GNT3). Also, we have identified 15 de novo variants in genes that were previously implicated in ASD or related neurodevelopmental disorders (PHF21A, WASF1, TCF20, DEAF1, MED13, CREBBP, KDM6B, SMURF1, ADNP, CACNA1G, MYT1L, KIF13B, GRIA2, CHM, and KCNK9). Additionally, we defined eight novel recessive variants (RYR2, DNAH3, TSPYL2, UPF3B KDM5C, LYST, and WNK3), four of which were X-linked. Conclusion: Despite the ASD multifactorial etiology that hinders ASD genetic risk discovery, the number of identified novel or known putative ASD genetic variants was appreciable. Nevertheless, this study represents the first comprehensive characterization of ASD genetic risk in Qatar's Middle Eastern population.

Temtamy syndrome caused by a new C12orf57 variant in a Chinese boy, including pedigree analysis and literature review

Temtamy syndrome is an extremely rare disorder caused by chromosome 12 open reading frame 57 (C12orf57) pathogenic variants. The present study reported a boy with Temtamy syndrome displaying global developmental delay, epilepsy and dysmorphic facial appearance. Whole-exome sequencing was performed to identify a novel homozygous pathogenic variant of C12orf57 (c.3G >C, p.Met1IIe), and the affected protein structure and function were predicted to be pathogenic. Additionally, clinical features of the other reported 56 patients with C12orf57 pathogenic variants were reviewed and compared. This study highlighted that C12orf57 pathogenic variants are mainly associated with global developmental delay, epilepsy and dysmorphic facial appearances. The clinical features were in accordance with the previously reported cases, except for those with recurrent infection, but without corpus callosum abnormalities. The present study reported the first Asian case to the best of our knowledge with Temtamy syndrome, and the novel C12orf57 pathogenic variant has not reported in any ethnic groups previously. The present study expanded the spectrum of C12orf57 pathogenic variants as well as the ethnic backgrounds of the affected patients.

Genetics of anophthalmia and microphthalmia. Part 1: Non-syndromic anophthalmia/microphthalmia

Eye formation is the result of coordinated induction and differentiation processes during embryogenesis. Disruption of any one of these events has the potential to cause ocular growth and structural defects, such as anophthalmia and microphthalmia (A/M). A/M can be isolated or occur with systemic anomalies, when they may form part of a recognizable syndrome. Their etiology includes genetic and environmental factors; several hundred genes involved in ocular development have been identified in humans or animal models. In humans, around 30 genes have been repeatedly implicated in A/M families, although many other genes have been described in single cases or families, and some genetic syndromes include eye anomalies occasionally as part of a wider phenotype. As a result of this broad genetic heterogeneity, with one or two notable exceptions, each gene explains only a small percentage of cases. Given the overlapping phenotypes, these genes can be most efficiently tested on panels or by whole exome/genome sequencing for the purposes of molecular diagnosis. However, despite whole exome/genome testing more than half of patients currently remain without a molecular diagnosis. The proportion of undiagnosed cases is even higher in those individuals with unilateral or milder phenotypes. Furthermore, even when a strong gene candidate is available for a patient, issues of incomplete penetrance and germinal mosaicism make diagnosis and genetic counseling challenging. In this review, we present the main genes implicated in non-syndromic human A/M phenotypes and, for practical purposes, classify them according to the most frequent or predominant phenotype each is associated with. Our intention is that this will allow clinicians to rank and prioritize their molecular analyses and interpretations according to the phenotypes of their patients.

Genes and pathways in optic fissure closure

Embryonic development of the vertebrate eye begins with the formation of an optic vesicle which folds inwards to form a double-layered optic cup with a fissure on the ventral surface, known as the optic fissure. Closure of the optic fissure is essential for subsequent growth and development of the eye. A defect in this process can leave a gap in the iris, retina or optic nerve, known as a coloboma, which can lead to severe visual impairment. This review brings together current information about genes and pathways regulating fissure closure from human coloboma patients and animal models. It focuses especially on current understanding of the morphological changes and processes of epithelial remodelling occurring at the fissure margins.

Agenesis of the corpus callosum: a clinical approach to diagnosis

This review article aims to guide the clinician in establishing a diagnosis in patients with agenesis of the corpus callosum (ACC), presenting antenatally or postnatally. ACC may be isolated, or occur in association with other neuroanatomical lesions and/or congenital anomalies, and has many different genetic causes. Neuropsychological outcome varies considerably from normal to profound intellectual disability depending on the etiology. Approximately 25% of individuals with antenatally diagnosed apparently isolated ACC have intellectual disability. Subtle neurological, social, and learning deficits may still occur in those with normal intelligence and longitudinal neurocognitive follow-up is recommended for all children with ACC. The finding of ACC should prompt detailed clinical assessment in order to determine and manage the underlying condition. It is recognized that genetic factors contribute to ACC in the vast majority of cases. Less commonly ACC can result from antenatal infections, vascular or toxic insults, and it is increasingly recognized that ACC, particularly isolated ACC, may be due to an interaction of a number of "modifier" genetic and environmental factors. There are a large number of genetic conditions in which ACC may be a feature. We suggest a diagnostic algorithm to help guide the clinician towards diagnosis, to provide outcome advice and to aid in genetic counseling.

Exome sequencing identifies compound heterozygous mutations in C12orf57 in two siblings with severe intellectual disability, hypoplasia of the corpus callosum, chorioretinal coloboma, and intractable seizures

In patients with genetically heterogeneous disorders such as intellectual disability or epilepsy, exome sequencing is a powerful tool to elucidate the underlying genetic cause. Homozygous and compound heterozygous mutations in C12orf57 have recently been described to cause an autosomal recessive syndromic form of intellectual disability, including agenesis/hypoplasia of the corpus callosum, optic coloboma, and intractable seizures. Here, we report on two siblings from nonconsanguineous parents harboring two compound heterozygous loss-of-function mutations in C12orf57 identified by exome sequencing, including a novel nonsense mutation, and review the patients described in the literature.