Germline mutations in HRAS proto-oncogene cause Costello syndrome

Costello syndrome is a multiple congenital anomaly and mental retardation syndrome characterized by coarse face, loose skin, cardiomyopathy and predisposition to tumors. We identified four heterozygous de novo mutations of HRAS in 12 of 13 affected individuals, all of which were previously reported as somatic and oncogenic mutations in various tumors. Our observations suggest that germline mutations in HRAS perturb human development and increase susceptibility to tumors.

Epilepsy and neurological findings in 11 individuals with 1p36 deletion syndrome

The 1p36 deletion syndrome is a newly delineated multiple congenital anomalies/mental retardation syndrome characterized by mental retardation, growth delay, epilepsy, congenital heart defects, characteristic facial appearance, and precocious puberty. We analyzed 11 patients by fluorescence in situ hybridization (FISH) using commercially available bacterial artificial chromosome and P1-derived artificial chromosome genomic clones to define the chromosomal deletion responsible for the 1p36 deletion syndrome. Cytogenetic investigation revealed two cases with a terminal deletion of 1p36. Nine patients had an apparently normal karyotype with standard G-bands by trypsin using Giemsa (GTG), but FISH screening with the highly polymorphic genetic marker D1Z2, which is mapped to 1p36.3 and contains an unusual reiterated 40-bp variable number tandem repeat, revealed a submicroscopic deletion. All patients had severe to profound mental retardation. Based on the University of California Santa Cruz Genome Browser, we constructed a deletion map and analyzed the relationship between neurological findings and chromosomal deletions for the 11 cases. Six cases had intractable epilepsy and three had no seizures. The common deletion interval was about 1 million base pairs (Mbp) located between RP11-82D16 and RP4-785P20 (Rho guanine exchange factor (GEF) 16). The severity of clinical symptoms correlates with the size of the deletion. This is demonstrated by the 3 patients with at least 8Mbp deletions that display profound mental retardation and congenital heart defects. Although haploinsufficiency of the potassium channel beta-subunit (KCNAB2) is thought to be responsible for intractable seizures in the 1p36 deletion syndrome, this was not the case for 3 of the 11 patients in this study. Further investigation of the 1p36 region is necessary to allow identification of genes responsible for the 1p36 deletion syndrome.

Functional analysis of PTPN11/SHP-2 mutants identified in Noonan syndrome and childhood leukemia

Noonan syndrome (NS) is characterized by short stature, characteristic facial features, and heart defects. Recently, missense mutations of PTPN11, the gene encoding protein tyrosine phosphatase (PTP) SHP-2, were identified in patients with NS. Further, somatic mutations in PTPN11 were detected in childhood leukemia. Recent studies showed that the phosphatase activities of five mutations identified in NS and juvenile myelomonocytic leukemia (JMML) were increased. However, the functional properties of the other mutations remain unidentified. In this study, in order to clarify the differences between the mutations identified in NS and leukemia, we examined the phosphatase activity of 14 mutants of SHP-2. We identified nine mutations, including a novel F71I mutation, in 16 of 41 NS patients and two mutations, including a novel G503V mutation, in three of 29 patients with leukemia. Immune complex phosphatase assays of individual mutants transfected in COS7 cells showed that ten mutants identified in NS and four mutants in leukemia showed 1.4-fold to 12.7-fold increased activation compared with wild-type SHP-2. These results suggest that the pathogenesis of NS and leukemia is associated with enhanced phosphatase activity of mutant SHP-2. A comparison of the phosphatase activity in each mutant and a review of previously reported cases showed that high phosphatase activity observed in mutations at codons 61, 71, 72, and 76 was significantly associated with leukemogenesis.

Elevated catecholamine metabolites in patients with Costello syndrome

Costello syndrome is a rare congenital anomaly syndrome with a predisposition to specific tumors, including neuroblastoma, rhabdomyosarcoma, and transitional cell carcinoma of the bladder. The increased risk for solid tumors led to the proposal of a tumor screening protocol. A screening test for neuroblastoma consists of measuring catecholamine metabolites in urine, an assay that may also be used for diagnostic confirmation of a suspected catecholamine secreting tumor. We report eight patients with Costello syndrome with elevated catecholamine metabolites, vanillylmandelic acid (VMA) and/or homovanillic acid (HVA), in urine. Each patient had additional laboratory and/or imaging studies. None of the patients was found to have a neuroblastoma or another catecholamine secreting tumor. In two cases, the assays were performed because the patients were symptomatic with diaphoresis and hypertension, respectively, and in the other six cases the assays were performed in order to screen for neuroblastoma. The pathophysiology for the catecholamine metabolite abnormality in these patients with Costello syndrome remains unclear. However, it appears that in this patient group an elevation above the normal limit, defined as 2 standard deviations (SD) above the mean for age, is more likely to be a variant, rather than a sign of a neuroblastoma. Thus, it may be prudent not to use this assay as a screening test, and to take the frequently elevated results into consideration when interpreting diagnostic assays.

Fifty microdeletions among 112 cases of Sotos syndrome: Low copy repeats possibly mediate the common deletion

Sotos syndrome (SoS) is an autosomal dominant overgrowth syndrome with characteristic craniofacial dysmorphic features and various degrees of mental retardation. We previously showed that haploinsufficiency of the NSD1 gene is the major cause of SoS, and submicroscopic deletions at 5q35, including NSD1, were found in about a half (20/42) of our patients examined. Since the first report, an additional 70 SoS cases consisting of 53 Japanese and 17 non-Japanese have been analyzed. We found 50 microdeletions (45%) and 16 point mutations (14%) among all the 112 cases. A large difference in the frequency of microdeletions between Japanese and non-Japanese patients was noted: 49 (52%) of the 95 Japanese patients and only one (6%) of the 17 non-Japanese had microdeletions. A sequence-based physical map was constructed to characterize the microdeletions. Most of the microdeletions were confirmed to be identical by FISH analysis. We identified highly homologous sequences, i.e., possible low copy repeats (LCRs), in regions flanking proximal and distal breakpoints of the common deletion, This suggests that LCRs may mediate the deletion. Such LCRs seem to be present in different populations. Thus the different frequency of microdeletions between Japanese and non-Japanese cases in our study may have been caused by patient-selection bias.

Preferential paternal origin of microdeletions caused by prezygotic chromosome or chromatid rearrangements in Sotos syndrome

Sotos syndrome (SoS) is characterized by pre- and postnatal overgrowth with advanced bone age; a dysmorphic face with macrocephaly and pointed chin; large hands and feet; mental retardation; and possible susceptibility to tumors. It has been shown that the major cause of SoS is haploinsufficiency of the NSD1 gene at 5q35, because the majority of patients had either a common microdeletion including NSD1 or a truncated type of point mutation in NSD1. In the present study, we traced the parental origin of the microdeletions in 26 patients with SoS by the use of 16 microsatellite markers at or flanking the commonly deleted region. Deletions in 18 of the 20 informative cases occurred in the paternally derived chromosome 5, whereas those in the maternally derived chromosome were found in only two cases. Haplotyping analysis of the marker loci revealed that the paternal deletion in five of seven informative cases and the maternal deletion in one case arose through an intrachromosomal rearrangement, and two other cases of the paternal deletion involved an interchromosomal event, suggesting that the common microdeletion observed in SoS did not occur through a uniform mechanism but preferentially arose prezygotically.

Further delineation of the behavioral and neurologic features in Costello syndrome

To describe clinical and neurodevelopmental phenotypes of Costello syndrome, we performed a retrospective review of the clinical records and findings in 10 children with Costello syndrome. All patients showed significant postnatal growth retardation and severe feeding difficulties leading to failure to thrive from early infancy. All required tube feeding and some needed high-calorie formulas for variable periods. Developmental quotients/IQs in seven children were 50 or less, and three were in the mildly retarded range. Five had seizures. Remarkable manifestations not previously reported were the characteristic behavior in infancy. Although happy and sociable personality was always emphasized in the genetic literature, all children showed significant irritability, including hypersensitivity to sound and tactile stimuli, sleep disturbance, and excess shyness with strangers in infancy. Those symptoms usually disappeared around age 2-4 years. Other clinical signs included cardiac abnormalities (8), musculoskeletal abnormalities (10), ophthalmological manifestations (5), increased urinary vanillymandelic acid (VMA) and homovanillic acid (HVA) (3), rhabdomyosarcoma (1), laryngomalacia (1), and cryptorchidism (1). Only three girls had papillomata. Family histories were negative for Costello syndrome. In conclusion, we confirm the wide spectrum of mental function in patients with Costello syndrome, which ranges from severe to mild. During infancy Costello syndrome showed remarkable irritability with severe feeding problems, which attributes significant difficulties to the parents of affected children.

Patellar dislocation in Kabuki syndrome

We describe four individuals (two females and two males) with Kabuki syndrome and recurrent dislocation of the patella. The age of diagnosis of patellar dislocation ranged from 11 to 23 years. One individual underwent excision of the free fragment and transfer of the tibial tuberosity with good outcome. Two required patellar brace for instability. Characteristics of individuals with the syndrome at a high risk of patellar dislocation include female, adolescence or young adulthood, joint laxity, and obesity.

[Analysis of 14 individuals who requested predictive genetic testing for hereditary neuromuscular diseases]

Predictive genetic testing for hereditary neuromuscular diseases is a delicate issue for individuals at risk and their families, as well as for medical staff because these diseases are often late-onset and intractable. Therefore careful pre- and post-test genetic counseling and psychosocial support should be provided along with such genetic testing. The Division of Clinical and Molecular Genetics was established at our hospital in May 1996 to provide skilled professional genetic counseling. Since its establishment, 14 individuals have visited our clinic to request predictive genetic testing for hereditary neuromuscular diseases (4 for myotonic dystrophy, 6 for spinocerebellar ataxia, 3 for Huntington's disease, and 1 for Alzheimer's disease). The main reasons for considering testing were to remove uncertainty about the genetic status and to plan for the future. Nine of 14 individuals requested testing for making decisions about a forthcoming marriage or pregnancy (family planning). Other reasons raised by the individuals included career or financial planning, planning for their own health care, and knowing the risk for their children. At the first genetic counseling session, all of the individuals expressed hopes of not being a gene carrier and of escaping from fear of disease, and seemed not to be mentally well prepared for an increased-risk result. To date, 7 of the 14 individuals have received genetic testing and only one, who underwent predictive genetic testing for spinocerebellar ataxia, was given an increased-risk result. The seven individuals including the one with an increased-risk result, have coped well with their new knowledge about their genetic status after the testing results were disclosed. None of them has expressed regret. In pre-test genetic counseling sessions, we consider it quite important not only to determine the psychological status of the individual, but also to make the individual try to anticipate the changes in his/her life upon receiving an increased-risk or a decreased-risk result. Sufficient time should be taken to build a good relationship between the individual and his/her family and the medical staff during pre-test counseling sessions. This will help the individuals feel satisfied with their own decisions for the future, whether they receive genetic testing or not.

Graves' disease in patients with 22q11.2 deletion

We report 4 female patients and 1 male patient with a 22q11.2 deletion and Graves' disease diagnosed at age 27 months, 7, 10, 17, and 16 years, respectively. The clinical presentations were typical for hyperthyroidism, but 1 female infant had seizures in addition to symptoms of hyperthyroidism. All patients had elevated serum levels of thyroid hormones in association with suppressed thyroid-stimulating hormone levels. From these observations, we suggest that Graves' disease may be a part of the clinical spectrum associated with the 22q11.2 deletion syndrome.

Functional disomy for Xq26.3-qter in a boy with an unbalanced t(X;21)(q26.3;p11.2) translocation

A nine-month-old boy, with functional disomy for Xq26-qter and multiple congenital abnormalities, is reported. The boy had severe pre- and postnatal growth retardation, profound developmental delay, hypotonia, microcephaly, agenesis of the corpus callosum, dysmorphic facial features, cryptorchidism, and left multidysplastic kidney. He developed feeding difficulties and infantile spasms. G-banding analysis of his chromosomes showed additional material on the short arm of chromosome 21. His parents refused to submit to chromosome analysis. Analysis with chromosome microdissection followed by reverse and forward chromosome painting indicated his karyotype as 46,XY,der(21)t(X;21)(q26;p11.2). This is the first description of pure functional disomy for Xq26-qter due to an unbalanced X-autosome translocation.

[Clinical spectrum and management of holoprosencephaly]

To study the phenotypic spectrum and management of holoprosencephaly (HPE), we reviewed the findings of eight children with HPE from 3 to 10 years of age, who underwent intervention programs and rehabilitation at our center. One patient had alobar HPE, three semilobar HPE, and four lobar HPE. All patients had postnatal growth retardation, and seven showed a decreased BMI (< 25% tile). All patients had severe developmental delay and mental retardation (DQ < 40), showing no obvious correlation between their severity and the type of HPE. Neurologically seven patients had spasticity (3 spastic quadriplegia, 2 spastic diplegia, 2 mixed-type), except one patient with a 7q deletion [46,XY,del(7) (q35)] who had generalized hypotonia. Seven had variable types of seizures. All patients had feeding difficulties and were assessed by speech-language therapists. Four patients required tube feeding, four had gastroesophageal reflux disease. Recurrent respiratory tract infection was common. Three patients had abnormal serum sodium concentration (1 diabetes insipidus, 1 idiopathic hypernatremia, 1 hyponatremia). No family history of HPE was elicited. In conclusion, patients with HPE should be followed up closely for complications such as feeding difficulty, malnutrition, seizures, spasticity, infection, and osmoreceptor-hypothalamus-hypophyseal axis abnormalities.

Syndrome of microcephaly, Dandy-Walker malformation, and Wilms tumor caused by mosaic variegated aneuploidy with premature centromere division (PCD): report of a new case and review of the literature

We report a male infant with multiple congenital anomalies and mosaic variegated aneuploidy; a rare cytogenetic abnormality characterized by mosaicism for several different aneuploidies involving many different chromosomes. He had prenatal-onset growth retardation, microcephaly, dysmorphic face, seizures, hypotonia, feeding difficulty, and developmental delay. In addition, he developed bilateral Wilms tumors. Neuroradiological examination revealed Dandy-Walker malformation and hypoplasia of the cerebral hemisphere and pons. Cytogenetic analysis revealed various multiple numerical aneuploidies in blood lymphocytes, fibroblasts, and bone marrow cells, together with premature centromere division (PCD). Peripheral blood chromosome analysis from his parents also showed PCD, but no aneuploid cells. The clinical phenotype and multiple aneuploidies of the patient may be a consequence of the homozygous PCD trait inherited from his parents. Comparison with previously reported cases of multiple aneuploidy suggests that mosaic variegated aneuploidy with PCD may be a clinically recognizable syndrome with major phenotypes being mental retardation, microcephaly, structural brain anomalies (including Dandy-Walker malformation), and possible cancer predisposition.

A mild variant of Desbuquois dysplasia

On the basis of three newly observed cases (a pair of siblings and a sporadic case) and one previously reported case, we describe the clinical and radiological phenotype of a skeletal dysplasia resembling Desbuquois dysplasia. The skeletal alterations in the present disorder, including generalized osteopenia, mild modification of the vertebral endplates, epiphyseal flattening of the long bones, broad proximal femora with a spur-like projection of the lesser trochanters (a monkey wrench appearance of the proximal femora), and advanced carpal skeletal age, are almost identical to those of Desbuquois dysplasia. However, postnatal growth failure and minor spondylo-articular problems in the present disorder contrast with the conspicuous prenatal growth failure and severe spondylo-articular deformities of Desbuquois dysplasia. Short stature in the present disorder does not reach the degree of Desbuquois dysplasia. Molecular investigation of one patient excluded abnormalities of the diastrophic dysplasia sulphate transporter gene.

CONCLUSION

The combination of skeletal alterations identical to those of Desbuquois dysplasia with milder short stature and spondylo-articular problems in the present patients suggests the nosological proposal of "a mild variant of Desbuquois dysplasia".

Phenotypic spectrum and management issues in Kabuki syndrome

OBJECTIVE

To report the phenotypic spectrum and management issues of children with Kabuki syndrome (Niikawa-Kuroki syndrome) from North America.

DESIGN

A case series of children (n = 18) with clinical findings of Kabuki syndrome.

SETTING

Medical genetics clinics in Washington, Alaska, and Arizona.

RESULTS

Most patients had postnatal growth retardation, and all had developmental delay and hypotonia. Feeding difficulties, with or without cleft palate, were common; 5 patients required gastrostomy tube placement. Developmental quotients/IQs in all but 2 were 60 or less. Seizures were seen in less than half of the patients, but ophthalmologic and otologic problems were common, particularly recurrent otitis media. Congenital heart defects were present in 7 (39%); 3 patients underwent repair of coarctation of the aorta. Other features included urinary tract anomalies, malabsorption, joint hypermobility and dislocation, congenital hypothyroidism, idiopathic thrombocytopenic purpura, and in one patient, autoimmune hemolytic anemia and hypogammaglobulinemia. All patients had negative family histories for Kabuki syndrome.

CONCLUSIONS

Kabuki syndrome is a mental retardation-malformation syndrome affecting multiple organ systems, with a broad spectrum of neuromuscular dysfunction and mental ability. Given that 18 ethnically diverse patients were identified from 2 genetics programs, it appears that this syndrome is more common in North American non-Japanese patients than previously appreciated.

Osteogenesis imperfecta-like syndrome with severe mental retardation and extrapyramidal tract signs

We report a girl with a unique combination of malformations, including recurrent fractures, mental retardation with extrapyramidal tract signs and minor facial abnormalities. Generalised osteoporosis with overtubulation of long bones was similar to that of osteogenesis imperfecta (OI). However, the short tubular bones were distinctively undertubulated and wormian bones were not found. Based on clinical, laboratory and neuroradiological examinations, it was less likely that bone fragility was attributable to disuse bone atrophy related to her physical handicap and the neurological abnormalities secondary to brain insult. She is presumed to have a previously undescribed OI-like syndrome.

Very late DNA replication in the human cell cycle

G2 was defined originally as the temporal gap between the termination of DNA replication and the beginning of mitosis. In human cells, the G2 period was estimated to be 3-4 h. However, the absence of replicative DNA synthesis during this period designated G2 has never been shown conclusively. In this report, we show that, at some autosomal and X linked loci, programmed DNA replication continues within 90 min of mitosis. Furthermore, the major accumulation of cyclin B1, a cell-cycle marker that is usually ascribed to G2, overlaps extensively with very late DNA replication. We conclude that the G2 period is much shorter than previously thought and may, in some cells, be nonexistent.

Digital anomalies, microcephaly, and normal intelligence: new syndrome or Feingold syndrome?

We present four patients-two boys and their mother and an unrelated girl-with microcephaly, normal intelligence, and digital abnormalities. The hand abnormalities are characterized by brachydactyly with radial clinodactyly of the fourth and fifth fingers, ulnar clinodactyly of the second fingers, and an increased space between the second and third fingers associated with an abnormal palmar crease that extends to the ulnar border. The foot abnormalities include short toes with syndactyly of the fourth and fifth toes. The mother has normal intelligence, and her sons and the unrelated girl have normal development. Although similar digital abnormalities, microcephaly, and normal intelligence were described by Feingold in patients with gastrointestinal atresia, we think that our patients' findings represent a different condition. The most likely mode of inheritance is autosomal dominant. The clinical recognition of this syndrome will allow for appropriate genetic counseling as well as provision of information on natural history, i.e., normal intelligence.

Mutation prevalence among 47 unrelated Japanese patients with Gaucher disease: identification of four novel mutations

Utilizing PCR and PCR-SSCP analysis we investigated the prevalence of glucocerebrosidase gene mutations in 47 unrelated Japanese patients with Gaucher disease. Sixty alleles (63.8%) and 20 alleles (21.3%) were identified by analysis for common mutations and PCR-SSCP analysis, respectively. The L444P and F213I mutations were common, accounting for 41 alleles (43.6%) and 14 alleles (14.9%). R496C, D409H, S366G and 1447-1466 del ins TG mutations were identified in 5, 3, 3 and 3 alleles, respectively. The other mutations were unique. In spite of vigorous screening, 14 alleles (14.9%) could not be identified. Four novel mutations were identified by PCR-SSCP analysis: G189V, S366G, K413Q and R433G. These data indicate that besides the L444P mutation no other frequent mutation is present and there is broad heterogeneity of the glucocerebrosidase gene mutations in Japanese patients with Gaucher disease.

Mitochondrial encephalomyopathies preceded by de-Toni-Debré-Fanconi syndrome or focal segmental glomerulosclerosis

We report two rare cases of mitochondrial encephalomyopathies which were preceded by renal diseases. One occurred in an 11-year-old girl diagnosed with Kearns-Sayre syndrome, which was preceded by de-Toni-Debré-Fanconi syndrome 8 years previously. The other occurred in a 14-year-old girl diagnosed with mitochondrial myopathy, encephalopathy, lactic acidosis, and stroke-like episodes, who developed focal segmental glomerulosclerosis 3 years prior to confirmation of the diagnosis. Tissue from both patient demonstrated morphological abnormalities of the mitochondria in the distal renal tubular epithelium and leiomyocytes of the small renal artery. The present cases illustrate various clinical and morphologic evidence of renal diseases which may further our understanding of mitochondrial encephalomyopathies.

Mutation screening of 17 Japanese patients with neuropathic Gaucher disease

Using PCR and PCR-single strand conformation polymorphism (SSCP) we have identified gene mutations in 17 Japanese patients with neuropathic Gaucher disease (type 2, 9 cases; type 3, 8 cases). The L444P, F213I, D409H, and 1447 del 20 and 1447 ins TG mutations accounted for eight (type 2, 6; type 3, 2), seven (type 2, 2; type 3, 5), three (type 3), and three (type 2) alleles, respectively. Three alleles were unique. Ten alleles (type 2, 5; type 3, 5) could not be identified. The genotypes, D409H/?, L444P/?, L444P/F213I, and F213I/?, were identified in three, three, two, and two patients, respectively. Six patients had a unique genotype and none of the mutant alleles could be identified in one patient. The data indicate that the genotypes in Japanese patients with neuropathic Gaucher disease are found to be heterogeneous and the genotype prevalence and mutated alleles are unique.

Allele-specific replication timing in imprinted domains: absence of asynchrony at several loci

Using a bromodeoxyuridine incorporation method to detect replicated DNA, we studied allele-specific replication of several sites within the human Prader-Willi/Angelman and IGF2/H19 imprinted regions. No obvious allele-specific differences in time of replication were detected at most loci previously reported to replicate asynchronously in the same cell types as determined by a FISH-based replication assay. Our finding of an absence of allelic replication asynchrony may be related to low levels of imprinted gene expression near these loci in the examined cells (lymphocytes, fibroblasts and lymphoblastoid cells). This view is supported by our studies of the imprinted SNRPN gene in that cells with paternal allele-specific expression (lymphocytes and lymphoblasts) replicate SNRPN alleles asynchronously, whereas cells with a low level of expression (HeLa) replicate SNRPN later and with less allelic asynchrony. In lymphoblasts, the early replicating allele of SNRPN was identified as the paternal one based on the properties of maternal allele-specific methylation and paternal allele-specific expression. Our studies suggest that FISH data implying replication asynchrony in nonexpressing cells reflect structural differences between the maternal and paternal alleles rather than differences in replication timing.