A novel FBXO28 frameshift mutation in a child with developmental delay, dysmorphic features, and intractable epilepsy: A second gene that may contribute to the 1q41-q42 deletion phenotype.

Chromosome 1q41-q42 deletions have recently been associated with a recognizable neurodevelopmental syndrome of early childhood (OMIM 612530). Within this group, a predominant phenotype of developmental delay (DD), intellectual disability (ID), epilepsy, distinct dysmorphology, and brain anomalies on magnetic resonance imaging/computed tomography has emerged. Previous reports of patients with de novo deletions at 1q41-q42 have led to the identification of an evolving smallest region of overlap which has included several potentially causal genes including DISP1, TP53BP2, and FBXO28. In a recent report, a cohort of patients with de novo mutations in WDR26 was described that shared many of the clinical features originally described in the 1q41-q42 microdeletion syndrome (MDS). Here, we describe a novel germline FBXO28 frameshift mutation in a 3-year-old girl with intractable epilepsy, ID, DD, and other features which overlap those of the 1q41-q42 MDS. Through a familial whole-exome sequencing study, we identified a de novo FBXO28 c.972_973delACinsG (p.Arg325GlufsX3) frameshift mutation in the proband. The frameshift and resulting premature nonsense mutation have not been reported in any genomic database. This child does not have a large 1q41-q42 deletion, nor does she harbor a WDR26 mutation. Our case joins a previously reported patient also in whom FBXO28 was affected but WDR26 was not. These findings support the idea that FBXO28 is a monogenic disease gene and contributes to the complex neurodevelopmental phenotype of the 1q41-q42 gene deletion syndrome.

Refinement of the critical region of 1q41q42 microdeletion syndrome identifies FBXO28 as a candidate causative gene for intellectual disability and seizures.

A clinically recognizable syndrome associated with 1q41q42 microdeletion has recently been described in the literature (OMIM 612530). Patients with microdeletions in this region of chromosome 1 typically have developmental delay, characteristic dysmorphic features, and a predisposition to seizures. Malformations such as congenital diaphragmatic hernia and cleft lip have also been described. There has been considerable interest in mapping the smallest region of overlap for this syndrome in order to identify the critical pathogenic genes. The smallest region of overlap has recently been refined to a region encompassing four genes. Using array comparative genome hybridization (array CGH), we have identified a female with a 590-kB deletion within chromosome1q41q42. This patient's deletion further refines the previously defined region of overlap to a single gene, FBXO28. We propose that FBXO28 is a possible candidate causative gene contributing to the intellectual disability and seizure phenotype observed in 1q41q42 microdeletion syndrome.

Molecular cytogenetic characterization of a de novo chromosome 1q41-q42.11 microdeletion of paternal origin in a 15-year-old boy with mental retardation, developmental delay, autism and congenital heart defects.

OBJECTIVE: We present molecular cytogenetic characterization of a de novo chromosome 1q41-q42.11 microdeletion of paternal origin in a mentally retarded child of a family requesting for genetic counseling of the future pregnancy. CASE REPORT: A 43-year-old, gravida 1, para 1, woman, who had a 15-year-old son with mental retardation, planned to have another normal child and requested for genetic counseling of the future pregnancy. Her husband was 48 years old. The 15-year-old boy had a body height of 148 cm (<3rd centile) and a body weight of 40 Kg (<35th centile). He had facial dysmorphism, mental retardation, scoliosis, abnormal gaits, tetralogy of Fallot, pulmonary stenosis and autism but did not have any history of epilepsy. Cytogenetic analysis of the boy and the parents revealed normal karyotypes. Array comparative genomic hybridization (aCGH) analysis of the family revealed a de novo 2.028-Mb 1q41-q42.11 microdeletion, or arr 1q41q42.11 (222,571,596-224,599,234) × 1.0 [GRCh37 (hg19)], encompassing 13 Online Mendelian Inheritance in Man (OMIM) genes including DISP1, SUSD4, FBXO28, TP53BP2 and WDR26 in the child. Quantitative fluorescent polymerase chain reaction analysis confirmed a paternal origin of the deletion. Fluorescence in situ hybridization analysis confirmed a 1q41 deletion. CONCLUSION: Genetic counseling of the parents who have a previous child with mental retardation and who wish to have another normal child in the future pregnancy should include genetic studies, and aCGH is useful under such a circumstance.