NFIB Haploinsufficiency Is Associated with Intellectual Disability and Macrocephaly.

The nuclear factor I (NFI) family of transcription factors play an important role in normal development of multiple organs. Three NFI family members are highly expressed in the brain, and deletions or sequence variants in two of these, NFIA and NFIX, have been associated with intellectual disability (ID) and brain malformations. NFIB, however, has not previously been implicated in human disease. Here, we present a cohort of 18 individuals with mild ID and behavioral issues who are haploinsufficient for NFIB. Ten individuals harbored overlapping microdeletions of the chromosomal 9p23-p22.2 region, ranging in size from 225 kb to 4.3 Mb. Five additional subjects had point sequence variations creating a premature termination codon, and three subjects harbored single-nucleotide variations resulting in an inactive protein as determined using an in vitro reporter assay. All individuals presented with additional variable neurodevelopmental phenotypes, including muscular hypotonia, motor and speech delay, attention deficit disorder, autism spectrum disorder, and behavioral abnormalities. While structural brain anomalies, including dysgenesis of corpus callosum, were variable, individuals most frequently presented with macrocephaly. To determine whether macrocephaly could be a functional consequence of NFIB disruption, we analyzed a cortex-specific Nfib conditional knockout mouse model, which is postnatally viable. Utilizing magnetic resonance imaging and histology, we demonstrate that Nfib conditional knockout mice have enlargement of the cerebral cortex but preservation of overall brain structure and interhemispheric connectivity. Based on our findings, we propose that haploinsufficiency of NFIB causes ID with macrocephaly.

Chromosome 17q12 duplications: Further delineation of the range of psychiatric and clinical phenotypes.

Copy number variants at chromosome 17q12 have been associated with a spectrum of phenotypes. Deletions of 17q12 are well described and associated with maturity onset diabetes of the young type 5 (MODY5) and cystic renal disease (HNF1ß) as well as cognitive impairment and seizures. Duplication of 17q12 is emerging as a new genetic syndrome, associated with learning disability, seizures, and behavioral problems. The duplication is often inherited from an apparently unaffected parent. Here, we describe a three-generation family with multiple individuals carrying a17q12 microduplication with varying clinical features, consistent with variable penetrance. The proband who inherited a 1.8 Mb interstitial 17q12 duplication from his mother presented with developmental delay, behavioral problems, and mild dysmorphism. One of his sisters, his maternal uncle, and his maternal grandmother also carry the 17q12 microduplication. Clinical features of the carriers include renal problems, diabetes mellitus, learning difficulties, epilepsy and mental illness. Cognitive abilities range from normal function to moderate impairment (full-scale IQ range: 52-99). In light of recent reports of association of this locus with schizophrenia, we performed a detailed psychiatric assessment and confirmed that one family member has symptoms consistent with a diagnosis of schizophrenia and another has a prodromal syndrome with attenuated positive symptoms of psychosis. This report extends the clinical phenotype associated with the 17q12 microduplication and highlights the phenotypic variability.

A rare example of germ-line chromothripsis resulting in large genomic imbalance.

Chromothripsis is a recently described 'chromosome catastrophe' phenomenon in which multiple genomic rearrangements are generated in a single catastrophic event. Chromothripsis has most frequently been associated with cancer, but there have also been rare reports of chromothripsis in patients with developmental disorders and congenital anomalies. In contrast to the massive DNA loss that often accompanies chromothripsis in cancer, only minimal DNA loss has been reported in the majority of cases of chromothripsis that have occurred in the germ line. Presumably, this is because in most instances, large genomic losses would be lethal in utero. We report on a female patient with developmental delay and dysmorphism. G-banded chromosome analysis detected a subtle, interstitial deletion of chromosome 13 and a complex rearrangement of one X chromosome. Subsequent array comparative genomic hybridisation studies indicated nine deletions on the X chromosome ranging from 327 kb to 8 Mb in size. A 4.4 Mb deletion on chromosome 13 was also confirmed, compatible with the patient's clinical phenotype. We propose that this is a rare example of constitutional chromothripsis in association with relatively large genomic imbalances and that these have been tolerated in this case as they have occurred in a female on the X chromosome, which has undergone preferential X inactivation.