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Costello syndrome (CS) entails a cancer predisposition and is caused by activating HRAS mutations, typically arising de novo in the paternal germline. Hypoglycemia is common in CS neonates. A previously reported individual with the rare HRAS p.Gln22Lys had hyperinsulinemic hypoglycemia. Autopsy showed a discrete pancreatic nodule. The morphologic and immunohistochemistry findings, including loss of p57(Kip2) protein, were identical to a focal lesion of congenital hyperinsulinism, however, no KCNJ11 or ABCC8 mutation was identified and germline derived DNA showed no alternation of the maternal or paternal 11p15 alleles. Here we report paternal uniparental disomy (pUPD) within the lesion, similar to the pUPD11p15.5 in Beckwith-Wiedemann syndrome (BWS). The similar extent of the pUPD suggests a similar mechanism driving hyperinsulinemia in both conditions. After coincidental somatic LOH and pUPD, the growth promoting effects of the paternally derived HRAS mutation, in combination with the increased function of the adjacent paternally expressed IGF2, may together result in clonal expansion. Although this somatic LOH within pancreatic tissue resulted in hyperinsulinism, similar LOH in mesenchymal cells may drive embryonal rhabdomyosarcoma (ERMS). Interestingly, biallelic IGF2 expression has been linked to rhabdomyosarcoma tumorigenesis and pUPD11 occurred in all 8 ERMS samples from CS individuals. Somatic KRAS and HRAS mutations occur with comparable frequency in isolated malignancies. Yet, the malignancy risk in CS is notably higher than in Noonan syndrome with a KRAS mutation. It is conceivable that HRAS co-localization with IGF2 and the combined effect of pUPD 11p15.5 on both genes contributes to the oncogenic potential.

Silver–Russell syndrome (SRS) is a heterogeneous disorder characterized by intrauterine and postnatal growth retardation, dysmorphic facial features and body asymmetry. Both hypomethylation of the telomeric imprinting control region 1 (ICR1) at 11p15.5 and maternal duplication of 11p15.5 have been implicated in the etiology of this disorder. Here we report the origin and segregation of the first reported between-arm intrachromosomal insertion of 11p15.5 that encompasses both ICR1 and ICR2 in a multigenerational family with a history of short stature. One (or any odd number) crossover within the centromeric segment during meiosis would produce recombinant chromosomes; one with a duplication of the inserted segment and the other a deletion. In this 4-generation family, there were six instances of transmission of the recombinant chromosome with duplication of the11p15.5 segment, which leads to a SRS phenotype when maternally inherited and a Beckwith–Wiedemann phenotype when paternally transmitted. The size of the duplicated region is ∼1.9 Mb as determined by microarray analysis. This study provides further evidence that maternally inherited duplications of 11p15.5 result in a SRS phenotype that includes short stature and other variable features. The methylation status of the extra copy of the duplicated region of 11p15.5 ultimately predicts the resulting phenotype. Thus, the different phenotype based on parental mode of transmission is of importance in the genetic counseling of these patients. © 2014 Wiley Periodicals, Inc.

We present three siblings with a precise onset of fetal seizure-like activity who had severe olivopontocerebellar hypoplasia (OPCH) and degeneration. Autopsies at 20, 27, and 37 weeks gestation showed diffuse central nervous system volume loss that was most marked for the cerebellum and brain stem structures. Neuropathological abnormalities included dysplastic, C-shaped inferior olivary nuclei, absent or immature dentate nuclei, and cell paucity more marked for the cerebellar vermis than the hemispheres. Delayed development was seen in layer 2 of the cerebral cortex and in Purkinje cells of the cerebellum. Prenatal monitoring defined a developmental window of 16-18 weeks gestation when ultrasonic assessment of cerebellar width was used for prenatal diagnosis. We discuss our findings in the context of the differential diagnosis for infantile (O)PCH and propose a classification scheme for the pontocerebellar hypoplasias. These patients represent the earliest reported with OPCH and provide unique information regarding the developmental neuropathology of this condition.

Adams-Oliver syndrome (AOS) consists of congenital scalp defects with variable limb defects of unknown pathogenesis. We report on two children with AOS plus additional features including intrauterine growth retardation (IUGR), cutis marmorata telangiectatica congenita (CMTC), pulmonary hypertension (PH), intracranial densities shown in one case to be sites of active bleeding and osteopenia. Autopsy in one case revealed defective vascular smooth muscle cell/pericyte coverage of the vasculature associated with two blood vessel abnormalities. Pericyte absence correlated with vessel dilatation while hyperproliferation of pericytes correlated with vessel stenosis. These findings suggest a unifying pathogenic mechanism for the abnormalities seen in AOS. These and previously reported cases establish that a subset of AOS patients is at high risk for PH.