Elevation of insulin-like growth factor binding protein-2 level in Pallister-Killian syndrome: implications for the postnatal growth retardation phenotype.

Pallister-Killian syndrome (PKS) is a multi-system developmental disorder caused by tetrasomy 12p that exhibits tissue-limited mosaicism. Probands with PKS often demonstrate a unique growth profile consisting of macrosomia at birth with deceleration of growth postnatally. We have previously demonstrated that cultured skin fibroblasts from PKS probands have significantly elevated expression of insulin-like growth factor binding protein-2 (IGFBP2). To further evaluate the role of IGFBP2 in PKS, the amount of IGFBP2 secreted from cultured skin fibroblast cell lines and serum IGFBP2 levels were measured in probands with PKS. Approximately 60% of PKS fibroblast cell lines secreted higher levels of IGFBP2 compared to control fibroblasts, although the remaining 40% of PKS samples produced comparable level of IGFBP2 to that of control fibroblasts. Serum IGFBP2 levels were also measured in PKS probands and were elevated in 40% of PKS probands. PKS probands with elevated IGFBP2 manifested with severe postnatal growth retardation. IGFBPs are the family of related proteins that bind IGFs with high affinity and are typically thought to attenuate IGF action. We suggest that elevated IGFBP2 levels might play a role in the growth retardation phenotype of PKS.

Cardiac manifestations of Pallister-Killian syndrome.

Pallister-Killian syndrome (PKS) is a sporadic multisystem genetic diagnosis characterized by facial dysmorphia, variable developmental delay and intellectual impairment, hypotonia, hearing loss, seizures, differences in skin pigmentation, temporal alopecia, diaphragmatic hernia, congenital heart defects, and other systemic abnormalities. Although congenital heart defects have been described in association with PKS, the full spectrum of heart disease is still not entirely known. Here, we describe the pattern of cardiac findings of 81 probands with PKS who have had at least one cardiac evaluation, demonstrating structural heart difference in 37% of our cohort (n = 30). Septal defects such as atrial or ventricular septal defects (n = 12) were the most commonly seen congenital heart differences. Additional findings included the occasional occurrence of bicuspid aortic valve, aortic dilatation, and cardiac hypertrophy/cardiomyopathy. We suggest cardiac evaluation for all individuals with PKS at the time of diagnosis as well as subsequent longitudinal follow-up to monitor for the development of cardiomyopathy and aortic dilatation.

ESRP1 Mutations Cause Hearing Loss due to Defects in Alternative Splicing that Disrupt Cochlear Development.

Alternative splicing contributes to gene expression dynamics in many tissues, yet its role in auditory development remains unclear. We performed whole-exome sequencing in individuals with sensorineural hearing loss (SNHL) and identified pathogenic mutations in Epithelial Splicing-Regulatory Protein 1 (ESRP1). Patient-derived induced pluripotent stem cells showed alternative splicing defects that were restored upon repair of an ESRP1 mutant allele. To determine how ESRP1 mutations cause hearing loss, we evaluated Esrp1-/- mouse embryos and uncovered alterations in cochlear morphogenesis, auditory hair cell differentiation, and cell fate specification. Transcriptome analysis revealed impaired expression and splicing of genes with essential roles in cochlea development and auditory function. Aberrant splicing of Fgfr2 blocked stria vascularis formation due to erroneous ligand usage, which was corrected by reducing Fgf9 gene dosage. These findings implicate mutations in ESRP1 as a cause of SNHL and demonstrate the complex interplay between alternative splicing, inner ear development, and auditory function.