Despite their clinical significance, characterization of balanced chromosomal abnormalities (BCAs) has largely been restricted to cytogenetic resolution. We explored the landscape of BCAs at nucleotide resolution in 273 subjects with a spectrum of congenital anomalies. Whole-genome sequencing revised 93% of karyotypes and revealed complexity that was cryptic to karyotyping in 21% of BCAs, highlighting the limitations of conventional cytogenetic approaches. At least 33.9% of BCAs resulted in gene disruption that likely contributed to the developmental phenotype, 5.2% were associated with pathogenic genomic imbalances, and 7.3% disrupted topologically associated domains (TADs) encompassing known syndromic loci. Remarkably, BCA breakpoints in eight subjects altered a single TAD encompassing MEF2C, a known driver of 5q14.3 microdeletion syndrome, resulting in decreased MEF2C expression. This study proposes that sequence-level resolution dramatically improves prediction of clinical outcomes for balanced rearrangements, and provides insight into novel pathogenic mechanisms such as altered regulation due to changes in chromosome topology.

The Koolen-de Vries syndrome (KdVS; OMIM #610443), also known as the 17q21.31 microdeletion syndrome, is a clinically heterogeneous disorder characterised by (neonatal) hypotonia, developmental delay, moderate intellectual disability, and characteristic facial dysmorphism. Expressive language development is particularly impaired compared with receptive language or motor skills. Other frequently reported features include social and friendly behaviour, epilepsy, musculoskeletal anomalies, congenital heart defects, urogenital malformations, and ectodermal anomalies. The syndrome is caused by a truncating variant in the KAT8 regulatory NSL complex unit 1 (KANSL1) gene or by a 17q21.31 microdeletion encompassing KANSL1. Herein we describe a novel cohort of 45 individuals with KdVS of whom 33 have a 17q21.31 microdeletion and 12 a single-nucleotide variant (SNV) in KANSL1 (19 males, 26 females; age range 7 months to 50 years). We provide guidance about the potential pitfalls in the laboratory testing and emphasise the challenges of KANSL1 variant calling and DNA copy number analysis in the complex 17q21.31 region. Moreover, we present detailed phenotypic information, including neuropsychological features, that contribute to the broad phenotypic spectrum of the syndrome. Comparison of the phenotype of both the microdeletion and SNV patients does not show differences of clinical importance, stressing that haploinsufficiency of KANSL1 is sufficient to cause the full KdVS phenotype.

Two autistic children with a chromosome 15q11‐q13 inverted duplication are presented. Both had uneventful perinatal courses, normal electroencephalogram and magnetic resonance imaging scans, moderate motor delay, lethargy, severe hypotonia, and modest lactic acidosis. Both had muscle mitochondrial enzyme assays that showed a pronounced mitochondrial hyperproliferation and a partial respiratory chain block most parsimoniously placed at the level of complex III, suggesting candidate gene loci for autism within the critical region may affect pathways influencing mitochondrial function. Ann Neurol 2003;53:801–804

Down syndrome is one of the most common conditions encountered in the genetics clinic. Due to improvements in healthcare, educational opportunities, and community inclusion over the past 30 years, the life expectancy and quality of life for individuals with Down syndrome have significantly improved. As prenatal screening and diagnostic techniques have become more enhanced and widely available, genetic counselors can expect to frequently provide information and support following a new diagnosis of Down syndrome. This guideline was written for genetic counselors and other healthcare providers regarding the communication of a diagnosis of Down syndrome to ensure that families are consistently given up-to-date and balanced information about the condition, delivered in a supportive and respectful manner.

Chromosome 4q deletion syndrome (4q- syndrome) is a rare condition, with an estimated incidence of 1 in 100,000. Although variable, the clinical spectrum commonly includes craniofacial, developmental, digital, skeletal, and cardiac involvement. Data on the genotype-phenotype correlation within the 4q arm are limited. We present detailed clinical and genetic information by array CGH on 20 patients with 4q deletions. We identified a patient who has a ∼465 kb deletion (186,770,069-187,234,800, hg18 coordinates) in 4q35.1 with all clinical features for 4q deletion syndrome except for developmental delay, suggesting that this is a critical region for this condition and a specific gene responsible for orofacial clefts and congenital heart defects resides in this region. Since the patients with terminal deletions all had cleft palate, our results provide further evidence that a gene associated with clefts is located on the terminal segment of 4q. By comparing and contrasting our patients' genetic information and clinical features, we found significant genotype-phenotype correlations at a single gene level linking specific phenotypes to individual genes. Based on these data, we constructed a hypothetical partial phenotype-genotype map for chromosome 4q which includes BMP3, SEC31A, MAPK10, SPARCL1, DMP1, IBSP, PKD2, GRID2, PITX2, NEUROG2, ANK2, FGF2, HAND2, and DUX4 genes.