ABSTRACT
Isolated congenital diaphragmatic hernia is often a sporadic event with a low recurrence risk. However, underlying genetic etiologies, such as chromosome anomalies or single gene disorders, are identified in a small number of individuals. We describe two fetuses with a unique pattern of multiple congenital anomalies, including diaphragmatic hernia, short bowel and asplenia, born to first-cousin parents. Whole exome sequencing showed that both were homozygous for a missense variant, c.950A>C, predicting p.Asp317Ala, in the H.20-Like Homeobox 1 (HLX1) gene. HLX is a homeobox transcription factor gene which is relatively conserved across species. Hlx homozygous null mice have a short bowel and reduced muscle cells in the diaphragm, closely resembling the anomalies in the two fetuses and we therefore suggest that the HLX mutation in this family could explain the fetal findings.
Subject(s)
Hernias, Diaphragmatic, Congenital/genetics , Heterotaxy Syndrome/genetics , Homeodomain Proteins/genetics , Short Bowel Syndrome/genetics , Transcription Factors/genetics , Abnormalities, Multiple/genetics , Abnormalities, Multiple/physiopathology , Animals , Digestive System Abnormalities/genetics , Digestive System Abnormalities/physiopathology , Genetic Predisposition to Disease , Hernias, Diaphragmatic, Congenital/physiopathology , Heterotaxy Syndrome/physiopathology , Humans , Mice , Mutation , Sequence Analysis, DNA , Short Bowel Syndrome/physiopathology , Exome SequencingABSTRACT
We describe the molecular and clinical characterization of nine individuals with recurrent, 3.4-Mb, de novo deletions of 3q13.2-q13.31 detected by chromosomal microarray analysis. All individuals have hypotonia and language and motor delays; they variably express mild to moderate cognitive delays (8/9), abnormal behavior (7/9), and autism spectrum disorders (3/9). Common facial features include downslanting palpebral fissures with epicanthal folds, a slightly bulbous nose, and relative macrocephaly. Twenty-eight genes map to the deleted region, including four strong candidate genes, DRD3, ZBTB20, GAP43, and BOC, with important roles in neural and/or muscular development. Analysis of the breakpoint regions based on array data revealed directly oriented human endogenous retrovirus (HERV-H) elements of ~5 kb in size and of >95% DNA sequence identity flanking the deletion. Subsequent DNA sequencing revealed different deletion breakpoints and suggested nonallelic homologous recombination (NAHR) between HERV-H elements as a mechanism of deletion formation, analogous to HERV-I-flanked and NAHR-mediated AZFa deletions. We propose that similar HERV elements may also mediate other recurrent deletion and duplication events on a genome-wide scale. Observation of rare recurrent chromosomal events such as these deletions helps to further the understanding of mechanisms behind naturally occurring variation in the human genome and its contribution to genetic disease.
Subject(s)
Chromosome Deletion , Chromosomes, Human, Pair 3/genetics , Cognition Disorders/genetics , Developmental Disabilities/genetics , Endogenous Retroviruses/genetics , Muscle Hypotonia/genetics , Adolescent , Adult , Base Sequence , Child , Child, Preschool , Chromosome Breakpoints , Cognition Disorders/diagnosis , Comparative Genomic Hybridization , Developmental Disabilities/diagnosis , Facies , Female , Gene Order , Humans , Infant , Male , Molecular Sequence Data , Muscle Hypotonia/diagnosis , Phenotype , Sequence Alignment , Syndrome , Young AdultABSTRACT
Branchio-oto-renal syndrome is a heterogeneous disorder inherited in an autosomal dominant pattern, characterized by branchial arch abnormalities, hearing loss and renal abnormalities, with mutations in EYA1 reported in 30-70% of patients. We have applied a molecular testing strategy of sequencing of the complete coding region/flanking intronic regions and multiple ligation probe amplification analysis of EYA1 to a pediatric branchio-oto-renal proband cohort. EYA1 mutations were identified in 82% (14/17) of the probands. We also describe a novel recurrent EYA1 mutation c.867 + 5G > A found in five unrelated affected patients. RNA analysis showed that c.867 + 5G > A affects EYA1 splicing, producing an aberrant mRNA transcript lacking exon 8 and resulting in premature termination in exon 9. The aberrant transcript was present at approximately 50% level of wild-type EYA1 mRNA in fibroblasts, and is predicted to encode an EYA1 protein retaining the amino terminal transcriptional coactivator region but lacking the conserved carboxy terminal Eya phosphatase domain. Patients with the c.867 + 5G > A mutation were found to have more severe renal abnormalities than probands with other mutations in this cohort. Analysis of the c.867 + 5G > A mutation suggests that certain transcripts of EYA1 escape nonsense-mediated decay and encode truncated EYA proteins that may be capable of dominant-negative interactions producing distinct phenotypic features within the branchio-oto-renal spectrum.
