Kosuke Izumi

Novel clinical manifestations in Pallister–Killian syndrome: Comprehensive evaluation of 59 affected individuals and review of previously reported cases

Pallister–Killian syndrome is a rare, multi‐system developmental diagnosis typically caused by tetrasomy of chromosome 12p that exhibits tissue‐limited mosaicism. The spectrum of clinical manifestations in Pallister–Killian syndrome is wide and includes craniofacial anomalies, clefts, ophthalmologic, audiologic, cardiac, musculoskeletal, diaphragmatic, gastrointestinal, genitourinary, and cutaneous anomalies in association with intellectual disability and seizures. Growth parameters are often normal to elevated at birth with deceleration of growth postnatally. No formal estimate of the prevalence of Pallister–Killian syndrome has been made. Here, we report the clinical findings in 59 individuals with Pallister–Killian syndrome who were ascertained at Pallister–Killian syndrome Foundation family meetings held in the summers of 2006, 2008, 2009, and 2010. In addition, the clinical findings of 152 cases reported in the medical literature were reviewed and compared to the cohort examined here. Several novel clinical characteristics were identified through detailed dysmorphology examinations of this cohort and reassertion of a mild developmental variant is described. This report expands the clinical manifestations of Pallister–Killian syndrome and highlights the variable expressivity of this diagnosis with important implications for diagnosis and counseling.

Hepatitis C Virus Impairs p53 via Persistent Overexpression of 3β-Hydroxysterol Δ24-Reductase

Persistent infection with hepatitis C virus (HCV) induces tumorigenicity in hepatocytes. To gain insight into the mechanisms underlying this process, we generated monoclonal antibodies on a genome-wide scale against an HCV-expressing human hepatoblastoma-derived cell line, RzM6-LC, showing augmented tumorigenicity. We identified 3β-hydroxysterol Δ24-reductase (DHCR24) from this screen and showed that its expression reflected tumorigenicity. HCV induced the DHCR24 overexpression in human hepatocytes. Ectopic or HCV-induced DHCR24 overexpression resulted in resistance to oxidative stress-induced apoptosis and suppressed p53 activity. DHCR24 overexpression in these cells paralleled the increased interaction between p53 and MDM2 (also known as HDM2), a p53-specific E3 ubiquitin ligase, in the cytoplasm. Persistent DHCR24 overexpression did not alter the phosphorylation status of p53 but resulted in decreased acetylation of p53 at lysine residues 373 and 382 in the nucleus after treatment with hydrogen peroxide. Taken together, these results suggest that DHCR24 is elevated in response to HCV infection and inhibits the p53 stress response by stimulating the accumulation of the MDM2-p53 complex in the cytoplasm and by inhibiting the acetylation of p53 in the nucleus.

Germline gain-of-function mutations in AFF4 cause a developmental syndrome functionally linking the super elongation complex and cohesin

Transcriptional elongation is critical for gene expression regulation during embryogenesis. The super elongation complex (SEC) governs this process by mobilizing paused RNA polymerase II (RNAP2). Using exome sequencing, we discovered missense mutations in AFF4, a core component of the SEC, in three unrelated probands with a new syndrome that phenotypically overlaps Cornelia de Lange syndrome (CdLS) that we have named CHOPS syndrome (C for cognitive impairment and coarse facies, H for heart defects, O for obesity, P for pulmonary involvement and S for short stature and skeletal dysplasia). Transcriptome and chromatin immunoprecipitation sequencing (ChIP-seq) analyses demonstrated similar alterations of genome-wide binding of AFF4, cohesin and RNAP2 in CdLS and CHOPS syndrome. Direct molecular interaction of the SEC, cohesin and RNAP2 was demonstrated. These data support a common molecular pathogenesis for CHOPS syndrome and CdLS caused by disturbance of transcriptional elongation due to alterations in genome-wide binding of AFF4 and cohesin.

Clinical Features of Three Girls With Mosaic Genome-Wide Paternal Uniparental Isodisomy

Here we describe three subjects with mosaic genome‐wide paternal uniparental isodisomy (GWpUPD) each of whom presented initially with overgrowth, hemihyperplasia (HH), and hyperinsulinism (HI). Due to the severity of findings and the presence of additional features, SNP array testing was performed, which demonstrated mosaic GWpUPD. Comparing these individuals to 10 other live‐born subjects reported in the literature, the predominant phenotype is that of pUPD11 and notable for a very high incidence of tumor development. Our subjects developed non‐metastatic tumors of the adrenal gland, kidney, and/or liver. All three subjects had pancreatic hyperplasia resulting in HI. Notably, our subjects to date display minimal features of other diseases associated with paternal UPD loci. Both children who survived the neonatal period have displayed near‐normal cognitive development, likely due to a favorable tissue distribution of the mosaicism. To understand the range of UPD mosaicism levels, we studied multiple tissues using SNP array analysis and detected levels of 5–95%, roughly correlating with the extent of tissue involvement. Given the rapidity of tumor growth and the difficulty distinguishing malignant and benign tumors in these GWpUPD subjects, we have utilized increased frequency of ultrasound (US) and alpha‐fetoprotein (AFP) screening in the first years of life. Because of a later age of onset of additional tumors, continued tumor surveillance into adolescence may need to be considered in these rare patients.

Utility of SNP arrays in detecting, quantifying, and determining meiotic origin of tetrasomy 12p in blood from individuals with Pallister-Killian syndrome.

Identification of the isochromosome 12p (i(12p)) associated with Pallister–Killian syndrome is complicated by the low frequency of this supernumerary chromosome in PHA stimulated peripheral blood lymphocytes, and frequently requires cytogenetic analysis of fibroblast cells. Recently, it has been shown that array CGH techniques are able to detect tetrasomy 12p in peripheral blood, even when not identified by traditional cytogenetic techniques. We studied 15 patients with a previous cytogenetic and clinical diagnosis of Pallister–Killian syndrome using genome‐wide SNP arrays to investigate the ability of this platform to identify the i(12p) in blood and tissue. Array analysis verified tetrasomy 12p in all samples from fibroblasts, but was only able to detect it in 46% of blood samples. The genotyping information available from the SNP arrays allowed for the detection of as low as 5% mosaicism, as well as suggesting a Meiosis II origin for the isochromosome in the majority of patients. Analysis of the percentage of abnormal cells with patient age at time of study suggests that the frequency of the i(12p) decreased with age in blood, but not in fibroblasts. These highlight the power of SNP arrays in detecting and characterizing the isochromosome 12p in Pallister–Killian syndrome as well as underscoring the important utility of traditional cytogenetic techniques.

Endocrine phenotype of 6q16.1–q21 deletion involving SIM1 and Prader–Willi syndrome-like features

Proximal interstitial 6q deletion involving Single‐minded 1 (SIM1) gene causes a syndromic form of obesity mimicking Prader–Willi syndrome. In addition to obesity, Prader–Willi syndrome includes several other endocrinopathies, such as hypothyroidism, growth hormone deficiency, and hypogonadotropic hypogonadism. The endocrine phenotype of interstitial 6q deletion remains largely unknown, although clinical similarities between Prader–Willi syndrome and interstitial 6q deletion suggest endocrine abnormalities also may contribute to the interstitial 6q deletion phenotype. This report describes the endocrine phenotype in a propositus with the Prader–Willi‐like syndrome associated with an interstitial 6q deletion including the SIM1 gene. Detailed endocrine evaluation of the propositus during childhood and adolescence revealed hypopituitarism, though initial endocrine evaluations during infancy were unremarkable. Our patient raises the possibility that hypopituitarism may be part of the phenotype, especially short stature, caused by interstitial 6q deletion. SIM1 plays an important role in the development of neuroendocrine lineage cells, implicating SIM1 haploinsufficiency in the pathophysiology of hypopituitarism seen in our propositus. Early identification of endocrine abnormalities can improve clinical outcome by allowing timely introduction of hormone replacement therapy. Hence, we suggest that detailed endocrine evaluation and longitudinal endocrine follow up be performed in individuals with proximal interstitial 6q deletion involving SIM1.

Duplication 12p and Pallister–Killian syndrome: A case report and review of the literature toward defining a Pallister–Killian syndrome minimal critical region†

Pallister–Killian syndrome (PKS) is a multisystem sporadic genetic condition characterized by facial anomalies, variable developmental delay and intellectual impairment, hypotonia, hearing loss, seizures, pigmentary skin differences, temporal alopecia, diaphragmatic hernia, congenital heart defects, and other systemic abnormalities. PKS is typically caused by the presence of a supernumerary isochromosome composed of the short arms of chromosome 12 resulting in tetrasomy 12p, which is often present in a tissue limited mosaic state. The PKS phenotype has also often been observed in individuals with complete or partial duplications of 12p (trisomy 12p rather than tetrasomy 12p) as the result of an interstitial duplication or unbalanced translocation. We have identified a proposita with PKS who has two small de novo interstitial duplications of 12p which, along with a review of previously reported cases, has allowed us to define a minimum critical region for PKS.

Tietz syndrome: unique phenotype specific to mutations of MITF nuclear localization signal

To the Editor: Microphthalmia-associated transcription factor (MITF) is a member of the basic helix-loop-helix leucine zipper family of transcription factors that regulate the development and maintenance of melanocytes and the biosynthetic pathway of melanin (1). Mutations in MITF lead to Waardenburg syndrome type 2A (WS2A) (2), an autosomal dominant disorder characterized by variable degrees of sensorineural hearing loss and patchy regional distribution of hypopigmentation including heterochromia of the iris, a white forelock, and spotty hypopigmentation. On rare occasions, mutations in MITF lead to the Tietz syndrome (TS) (3), which is distinguishable from WS2 in that TS is characterized by much severer phenotypes with generalized, rather than patchy, hypopigmentation and complete hearing loss (4). So far, only two families with TS have been published. Both these families have undergone molecular analyses: one family had a missense mutation (Asn210Lys) and the other had a 3-bp in-frame deletion [del (R217)] (3, 5). In this study, we present the results of molecular and histological studies conducted on a patient with typical TS. The proband was a 24-year-old woman with generalized pigment loss and congenital complete sensorineural hearing loss. Since her birth, she exhibited blue eyes’ and fair skin. The patient gradually developed freckles in sun-exposed regions at the age of 3 years. Her development was normal, except for her speech. Upon physical examination, she exhibited a generalized hypopigmentation of the skin, blue iridis and blond hair and eyebrows. Fundoscopic examination revealed lack of retinal pigmentation (Fig. 1). Based on these physical findings, she was diagnosed as having TS. Direct sequencing of the polymerase chain reaction products revealed a heterozygous 3-bp in-frame deletion in exon 7 of MITF, leading to a single amino acid deletion del (R217). The mutation was identical to that reported by Amiel et al. (3). Skin biopsy specimens were obtained from hypopigmented regions and hyperpigmented regions (i.e. freckles) on her leg and were processed for examination using light and electron microscopy (Fig. 2). The results are summarized in Table 1. The virtual lack of interfamilial variability among the two previously reported TS families and the present case establishes TS as a clinically recognizable entity (Table 2). The severity of the TS phenotype, compared with that of WS, may be explained from a stoichiometric standpoint: (i) the MITF protein functions as a homodimer, (ii) the mouse mi del (R217) MITF protein can interact with either the wild-type protein or itself when present in the cytoplasm, and (iii) dimers containing the mutant protein cannot be transported from the cytoplasm into the nucleus (6).

Pallister–Killian syndrome

Pallister–Killian syndrome (PKS) is characterized by craniofacial dysmorphism, pigmentary skin anomalies, congenital heart defects, congenital diaphragmatic hernia, hypotonia, intellectual disability, and epilepsy. PKS is caused by extra copies of chromosome 12p, most characteristically a marker isochromosome 12p that demonstrates tissue‐limited mosaicism. The cytogenetic diagnosis of PKS is often cumbersome due to the absence of the isochromosome in lymphocytes requiring sampling of other tissues. The mechanism by which the isochromosome 12p results in the constellation of multiple congenital anomalies remains largely unknown. In this review, we summarize the background of, and recent advances in, the clinical and molecular understanding of PKS.

Developmental and Behavioral Characteristics of Individuals With Pallister-Killian Syndrome

Pallister–Killian syndrome is a sporadic disorder caused by the presence of mosaic tetrasomy of the short arms of chromosome 12. Case reports of children with Pallister–Killian syndrome have described a range of developmental and behavioral outcomes, but no systematic studies of these outcomes exist. The objective of this study was to describe developmental and behavioral characteristics of individuals with Pallister–Killian syndrome participating in a national meeting of families and their affected children. Sixteen individuals with Pallister–Killian syndrome, ages 16 months to 19 years, were studied using questionnaires and direct interview. Among the 16 patients enrolled in the study, 3 probands were between 16 and 19 months, and had severe developmental delay. Among the rest of the 13 probands older than 24 months, 11 children had a developmental level of less than 8 months age equivalent. They were non‐ambulatory, non‐verbal, and passive, requiring extensive assistance in daily living. There were two higher functioning children who were ambulatory, and verbal. One of these children met criteria for Autism on the Autism Diagnostic Interview‐Revised. Thus, although most individuals with Pallister–Killian syndrome studied showed profound intellectual disability and sensory impairments, individuals with Pallister–Killian syndrome can have mild to moderate intellectual disability. Therefore, in individuals with physical examination findings of Pallister–Killian syndrome, formal diagnostic testing should be considered, even in individuals with mild to moderate intellectual disability. Further studies will be needed to determine if these higher functioning children with Pallister–Killian syndrome are at increased risk for autism.