Bernard N. Chodirker

Family history characteristics, tumor microsatellite instability and germline MSH2 and MLH1 mutations in hereditary colorectal cancer.

Recent characterization of the molecular genetic basis of hereditary nonpolyposis colorectal cancer provides an important opportunity for identification of individuals and their families with germline mutations in mismatch repair genes. Cancer family history criteria that accurately define hereditary colorectal cancer are necessary for cost-effective testing for germline mutations in mismatch repair genes. The present report describes the results of analysis of 33 colorectal cancer cases/families that satisfy our modified family history criteria (Mount Sinai criteria) for colorectal cancer. Fourteen of these families met the more stringent Amsterdam criteria. Germline MSH2 and MLH1 mutations were identified by the reverse transcription-polymerase chain reaction and the protein truncation test, and confirmed by sequencing. Microsatellite instability analysis was performed on available tumors from affected patients. MSH2 or MLH1 mutations were detected in 8 of 14 Amsterdam criteria families and in 5 of the remaining 19 cases/families that only satisfied the Mount Sinai criteria. Three of the latter families had features of the Muir-Torre syndrome. A high level of microsatellite instability (MSI-H) was detected in almost all (16/18) colorectal cancers from individuals with MSH2 and MLH1 mutations, and infrequently (1/21) in colorectal cancer specimens from cases without detectable mutations. Families with germline MSH2 and MLH1 mutations tended to have individuals affected at younger ages and with multiple tumors. The Amsterdam criteria are useful, but not sufficient, for detecting hereditary colorectal cancer families with germline MSH2 and MLH1 mutations, since a proportion of cases and families with mutations in mismatch repair genes will be missed. Further development of cancer family history criteria are needed, using unbiased prospectively collected cases, to define more accurately those who will benefit from MSH2 and MLH1 mutation analysis.

Genetic evaluation of pervasive developmental disorders: the terminal 22q13 deletion syndrome may represent a recognizable phenotype

The evaluation of mental retardation is always a challenge to clinicians. The recognition of specific physical or behavioral characteristics can vastly improve diagnostic yield. Several genetic disorders have been identified to have certain behavioral characteristics, such as Williams syndrome, Smith–Magenis syndrome, and the velocardiofacial syndrome (VCFS). The deletion affecting the chromosome 22q in the most distal band (22q13) appears to define yet another neurobehavioral phenotype. In addition to our report, there are about 17 other cases published of this particular deletion syndrome. We describe three children who share features of developmental delay and pervasive behaviors in addition to normal to advanced growth patterns. Results of cytogenetic analysis suggest that the 3 patients share a deletion affecting the terminal 22q13 region. Two were found to have a cryptic deletion, in the third it was detected by conventional cytogenetics. The cryptic deletions were demonstrated using fluorescent in situ hybridization (FISH), where the control probe for the DiGeorge/VCFS region was deleted. 
While there remain gaps in our understanding of this particular deletion syndrome, we propose that patients with normal or advanced growth, significantly delayed speech, deviant development and pervasive behaviors, with minor facial dysmorphism, be screened for this deletion.

An siRNA-based functional genomics screen for the identification of regulators of ciliogenesis and ciliopathy genes

Defects in primary cilium biogenesis underlie the ciliopathies, a growing group of genetic disorders. We describe a whole-genome siRNA-based reverse genetics screen for defects in biogenesis and/or maintenance of the primary cilium, obtaining a global resource. We identify 112 candidate ciliogenesis and ciliopathy genes, including 44 components of the ubiquitin–proteasome system, 12 G-protein-coupled receptors, and 3 pre-mRNA processing factors (PRPF6, PRPF8 and PRPF31) mutated in autosomal dominant retinitis pigmentosa. The PRPFs localize to the connecting cilium, and PRPF8- and PRPF31-mutated cells have ciliary defects. Combining the screen with exome sequencing data identified recessive mutations in PIBF1, also known as CEP90, and C21orf2, also known as LRRC76, as causes of the ciliopathies Joubert and Jeune syndromes. Biochemical approaches place C21orf2 within key ciliopathy-associated protein modules, offering an explanation for the skeletal and retinal involvement observed in individuals with C21orf2 variants. Our global, unbiased approaches provide insights into ciliogenesis complexity and identify roles for unanticipated pathways in human genetic disease.

Outcomes of genetic evaluation in children with pervasive developmental disorder

&NA; We undertook a retrospective etiological study of all children referred for evaluation of pervasive developmental disorder (PDD). We identified 91 children who met the DSM III‐R criteria for PDD. Fiftytwo were diagnosed with autistic disorder (AD), and 39 with PDD‐not otherwise specified (PDD‐NOS). Seven families (8.2%) had more than one affected sib. The overall recurrence rate was 7.1%. Six families had a positive history of PDD in more distant relatives. An excess of developmental problems were identified on the maternal side (seven families, vs two families on the paternal side). Affected children had head circumferences above the mean when compared with standardized growth curves. A recognizable syndrome or genetic disorder was identified in 14 children (15.4%), of which 8 children (9%) were thought to be causative of PDD (5 children with Rett syndrome, 2 with fragile X syndrome, and 1 with velocardiofacial syndrome [VCFS]). Six others had a recognized genetic, cytogenetic, or metabolic disorder believed to be unrelated to the PDD diagnosis. Given the relatively high yield of genetic diagnoses in this population, we believe that children with PDD‐NOS or AD should have a detailed evaluation by a clinical geneticist or pediatrician trained in dysmorphology. Chromosome anomalies, fragile X, and other recognizable disorders, including VCFS, need to be excluded. The value of general screening for an inborn error of metabolism in all children with PDD is not certain. In light of the relatively high recurrence of PDD in families, genetic counseling is recommended.

Mutations in CSPP1, Encoding a Core Centrosomal Protein, Cause a Range of Ciliopathy Phenotypes in Humans

Ciliopathies are characterized by a pattern of multisystem involvement that is consistent with the developmental role of the primary cilium. Within this biological module, mutations in genes that encode components of the cilium and its anchoring structure, the basal body, are the major contributors to both disease causality and modification. However, despite rapid advances in this field, the majority of the genes that drive ciliopathies and the mechanisms that govern the pronounced phenotypic variability of this group of disorders remain poorly understood. Here, we show that mutations in CSPP1, which encodes a core centrosomal protein, are disease causing on the basis of the independent identification of two homozygous truncating mutations in three consanguineous families (one Arab and two Hutterite) affected by variable ciliopathy phenotypes ranging from Joubert syndrome to the more severe Meckel-Gruber syndrome with perinatal lethality and occipital encephalocele. Consistent with the recently described role of CSPP1 in ciliogenesis, we show that mutant fibroblasts from one affected individual have severely impaired ciliogenesis with concomitant defects in sonic hedgehog (SHH) signaling. Our results expand the list of centrosomal proteins implicated in human ciliopathies.

Cryptic chromosome rearrangements detected by subtelomere assay in patients with mental retardation and dysmorphic features

The regions near telomeres of human chromosomes are gene rich. Chromosome subtelomere rearrangements occur with a frequency of 7–10% in children with mild‐to‐moderate mental retardation (MR) and approximately 50% of cases are familial. Clinical investigation of subtelomere rearrangements is now prompted by fluorescence in situ hybridization (FISH) analysis using specific DNA probes from all relevant chromosome ends. In our study, 40 children were selected for subtelomere assay using either the Chromophore Multiprobe‐T Cytocell device or the VYSIS TelVision probes. Inclusion criteria were: developmental delay or MR; a normal 550 G‐band karyotype; FRAXA negative; and at least one other clinical criterion. Exclusion criteria included an identified genetic or environmental diagnosis. Of the 40 patients analysed, four (10%) were found to have subtelomere rearrangements. Three of 40 (7.5%) were found to have an unbalanced subtelomere rearrangement and one of 40 (2.5%) was found to have an apparently normal variant subtelomere deletion. The first of the three with an unbalanced karyotype was the result of a familial translocation, the second was a de novo finding, and the origin of the third could not be determined. The subtelomere FISH assay detected almost twice the frequency of unbalanced karyotypes as those detected by 550 G‐banding in our cytogenetics laboratory (4.7%). In addition, subtelomere screening was eight times more likely than fragile X screening in our DNA laboratory (1%) to detect genetic abnormalities in mentally handicapped individuals. Our findings support the view that screening for subtelomere rearrangements has a greater positive yield than other commonly used genetic investigations and, if cost and resources permit, should be the next diagnostic test of choice in a child with unexplained MR/dysmorphisms and a normal 550 G‐band karyotype.

Infantile muscular dystrophy in Canadian aboriginals is an αB‐crystallinopathy

A recessively transmitted fatal hypertonic infantile muscular dystrophy has been described in Canadian aboriginals. The affected infants present with progressive limb and axial muscle stiffness and develop severe respiratory insufficiency, and most die in the first year of life. We sought to determine the genetic basis of this disease.

Fragile 19p13 in a family with mental illness

We describe a family where four brothers show the rare heritable folate sensitive autosomal fragile site (FSAFS) at 19pl3 when cells were grown in TCI99. Two of the brothers are schizophrenic while one brother is mentally retarded with autistic‐like features. The clinical significance of this fragile site however is still unknown.

Very low second-trimester maternal serum alpha-fetoprotein: Association with high birth weight.

OBJECTIVE To investigate the relationship between very low maternal serum alpha‐fetoprotein levels (MSAFP), neonatal size, and possible associations with obstetric complications. METHODS This is a retrospective case‐control study in a population managed prospectively by a standardized protocol. Perinatal outcomes were compared between patients with unexplained very low MSAFP (less than or equal to 0.25 multiples of the median) and control pregnancies with normal MSAFP, matched by precise gestational age, parity, maternal age within 1 year, and gender of the newborn. RESULTS Of the 84,909 women screened, 464 (0.55%) met the definition of very low MSAFP. On tertiary evaluation, 226 had dates reassigned by ultrasound. After exclusion of overt diabetics, patients who were not pregnant, invalidated MSAFP, and 17 patients lost to follow‐up, 178 women (0.21% of the total) had true very low MSAFP. True very low MSAFP was associated with subsequent miscarriage in 67 women and with fetal aneuploidy and/or serious abnormalities in 12 patients, leaving a population of 97 women (1.14 per 1000 women screened) with unexplained very low MSAFP. Without obvious demographic or obstetric factors, these women had heavier babies, more babies above the 90th percentile, more delivery complications caused by large birth weight (41 versus 16, χ2, P < .001) compared with gestational‐age matched controls from the same screened population who had normal MSAFP. CONCLUSION Very low MSAFP predicts an unusually high rate of large birth weight infants, with increased fetal, intrapartum, and neonatal consequences. Maternal medical conditions or obvious demographic factors do not explain these consequences. These findings suggest a role for close fetal surveillance in the third trimester and extended efforts to assess maternal and neonatal glucose status.

A novel mutation in KIAA0196: identification of a gene involved in Ritscher–Schinzel/3C syndrome in a First Nations cohort

Background Ritscher–Schinzel syndrome (RSS) is a clinically heterogeneous disorder characterised by distinctive craniofacial features in addition to cerebellar and cardiac anomalies. It has been described in different populations and is presumed to follow autosomal recessive inheritance. In an effort to identify the underlying genetic cause of RSS, affected individuals from a First Nations (FN) community in northern Manitoba, Canada, were enrolled in this study. Methods Homozygosity mapping by SNP array and Sanger sequencing of the candidate genes in a 1Mb interval on chromosome 8q24.13 were performed on genomic DNA from eight FN RSS patients, eight of their parents and five unaffected individuals (control subjects) from this geographic isolate. Results All eight patients were homozygous for a novel splice site mutation in KIAA0196. RNA analysis revealed an approximate eightfold reduction in the relative amount of a KIAA0196 transcript lacking exon 27. A 60% reduction in the amount of strumpellin protein was observed on western blot. Conclusions We have identified a mutation in KIAA0196 as the cause of the form of RSS characterised in our cohort. The ubiquitous expression and highly conserved nature of strumpellin, the product of KIAA0196, is consistent with the complex and multisystem nature of this disorder.