The power of the Mediator complex-Expanding the genetic architecture and phenotypic spectrum of MED12-related disorders.

MED12 is a member of the large Mediator complex that controls cell growth, development, and differentiation. Mutations in MED12 disrupt neuronal gene expression and lead to at least three distinct X-linked intellectual disability syndromes (FG, Lujan-Fryns, and Ohdo). Here, we describe six families with missense variants in MED12 (p.(Arg815Gln), p.(Val954Gly), p.(Glu1091Lys), p.(Arg1295Cys), p.(Pro1371Ser), and p.(Arg1148His), the latter being first reported in affected females) associated with a continuum of symptoms rather than distinct syndromes. The variants expanded the genetic architecture and phenotypic spectrum of MED12-related disorders. New clinical symptoms included brachycephaly, anteverted nares, bulbous nasal tip, prognathism, deep set eyes, and single palmar crease. We showed that MED12 variants, initially implicated in X-linked recessive disorders in males, may predict a potential risk for phenotypic expression in females, with no correlation of the X chromosome inactivation pattern in blood cells. Molecular modeling (Yasara Structure) performed to model the functional effects of the variants strongly supported the pathogenic character of the variants examined. We showed that molecular modeling is a useful method for in silico testing of the potential functional effects of MED12 variants and thus can be a valuable addition to the interpretation of the clinical and genetic findings.

PIK3R1 mutations in SHORT syndrome.

SHORT syndrome (OMIM 269880) is a rare autosomal-dominant disorder characterized by short stature, hyperextensibility of joints, hernias, ocular depression, ophthalmic anomalies (Rieger anomaly, posterior embryotoxon, glaucoma), teething delay, partial lipodystrophy, insulin resistance and facial dysmorphic signs. Heterozygous mutations in PIK3R1 were recently identified in 14 families with SHORT syndrome. Eight of these families had a recurrent missense mutation (c.1945C>T; p.Arg649Trp). We report on two unrelated patients with typical clinical features of SHORT syndrome and additional problems such as pulmonary stenosis and ectopic kidney. Analysis of PIK3R1 revealed the mutation c.1945C>T; p.Arg649Trp de novo in both patients. These two patients not only provide additional evidence that PIK3R1 mutations cause SHORT syndrome, but also broaden the clinical spectrum of this syndrome and further confirm that the amino acid exchange c.1945C>T; p.Arg649Trp is a hotspot mutation in this gene.

Parental origin of de novo cytogenetically balanced reciprocal non-Robertsonian translocations.

De novo cytogenetically balanced reciprocal non-Robertsonian translocations are rare findings in clinical cytogenetics and might be associated with an abnormal phenotype. Knowledge of the parental origin and mechanisms of formation is still limited. By microdissection of the derivative chromosomes and their normal homologs from metaphases followed by microsatellite-mediated marker analysis we identified 7 cases of paternal and 3 cases of maternal origin in a cohort of 10 patients with de novo cytogenetically balanced reciprocal non-Robertsonian translocations. Neither in the maternal nor in the paternal group of our study parental age seems to be increased. Together with the data from the literature our results confirm that the majority of de novo cytogenetically balanced reciprocal translocations are of paternal origin, but the preponderance does not appear to be as distinct as previously thought and the paternal age does not seem to be necessarily a major contributing factor.

A clinical and molecular genetic study of 112 Iranian families with primary microcephaly.

BACKGROUND: Primary microcephaly (MCPH) is a genetically heterogeneous disorder showing an autosomal recessive mode of inheritance. Affected individuals present with head circumferences more than three SDs below the age- and sex-matched population mean, associated with mild to severe mental retardation. Five genes (MCPH1, CDK5RAP2, ASPM, CENPJ, STIL) and two genomic loci, MCPH2 and MCPH4, have been identified so far. METHODS AND RESULTS: In this study, we investigated all seven MCPH loci in patients with primary microcephaly from 112 Consanguineous Iranian families. In addition to a thorough clinical characterisation, karyotype analyses were performed for all patients. For Homozygosity mapping, microsatellite markers were selected for each locus and used for genotyping. Our investigation enabled us to detect homozygosity at MCPH1 (Microcephalin) in eight families, at MCPH5 (ASPM) in thirtheen families. Three families showed homozygosity at MCPH2 and five at MCPH6 (CENPJ), and two families were linked to MCPH7 (STIL). The remaining 81 families were not linked to any of the seven known loci. Subsequent sequencing revealed eight, 10 and one novel mutations in Microcephalin, ASPM and CENPJ, respectively. In some families, additional features such as short stature, seizures or congenital hearing loss were observed in the microcephalic patient, which widens the spectrum of clinical manifestations of mutations in known microcephaly genes. CONCLUSION: Our results show that the molecular basis of microcephaly is heterogeneous; thus, the Iranian population may provide a unique source for the identification of further genes underlying this disorder.

Novel missense mutations in the ubiquitination-related gene UBE2A cause a recognizable X-linked mental retardation syndrome.

Recently, a truncating mutation of the UBE2A gene has been observed in a family with X-linked mental retardation (XLMR) (1). The three affected males had similar phenotypes, including seizures, obesity, marked hirsutism and a characteristic facial appearance. Here, we report on two families with a total of seven patients and a clinically very similar syndromic form of XLMR. Linkage analysis was performed in the larger of these families, and screening several positional candidate genes revealed a G23R missense mutation in the UBE2A gene. Subsequent UBE2A screening of a phenotypically similar second family revealed another missense mutation, R11Q, again affecting an evolutionarily conserved amino acid close to the N-terminus of the protein. SIFT and PolyPhen analyses suggest that both mutations are pathogenic, which is supported by their absence in 168 healthy controls. Thus, both missense and truncating mutations can give rise to a specific, syndromic form of XLMR which is identifiable in a clinical setting.

Hypergonadotropic hypogonadism in a patient with inv ins (2;4).

We report on a 30-year-old man with azoospermia, primary hypogonadism and minor dysmorphic features who carried a balanced insertional chromosome translocation inv ins (2p24;4q28.3q31.22)de novo. Molecular cytogenetic analyses of the chromosome breakpoints revealed the localization of the breakpoint in 4q28.3 between BACs RP11-143E9 and RP11-285A15, an interval that harbours the PCDH10 gene. In 4q31.22, a breakpoint-spanning clone (RP11-6L6) was identified which contains the genes LSM6 and SLC10A7. On chromosome 2, BACs RP11-531P14 and RP11-360O18 flank the breakpoint in 2p24, a region void of known genes. In conclusion, the chromosome aberration of this patient suggests a gene locus for primary hypogonadism in 2p24, 4q28.3 or 4q31.2, and three possible candidate genes (LSM6, SLC10A7 and PCDH10) were identified by breakpoint analyses.

High frequency of submicroscopic genomic aberrations detected by tiling path array comparative genome hybridisation in patients with isolated congenital heart disease.

BACKGROUND: Congenital heart disease (CHD) is the most common birth defect and affects nearly 1% of newborns. The aetiology of CHD is largely unknown and only a small percentage can be assigned to environmental risk factors such as maternal diseases or exposure to mutagenic agents during pregnancy. Chromosomal imbalances have been identified in many forms of syndromic CHD, but very little is known about the impact of DNA copy number changes in non-syndromic CHD. METHOD: A sub-megabase resolution array comparative genome hybridisation (CGH) screen was carried out on 105 patients with CHD as the sole abnormality at the time of diagnosis. RESULTS: There were 18 chromosomal changes detected, which do not coincide with common DNA copy number variants, including one de novo deletion, two de novo duplications and eight familial copy number variations (one deletion and seven duplications). CONCLUSIONS: Our data show that submicroscopic deletions and duplications play an important role in the aetiology of this condition, either as direct causes or as genetic risk factors for CHD. These findings have immediate consequences for genetic counselling and should pave the way for the elucidation of the pathogenetic mechanisms underlying CHD.

PUF60-SCRIB fusion transcript in a patient with 8q24.3 microdeletion and atypical Verheij syndrome.

Expression of the fusion genes is considered to be an important mechanism of tumorigenesis. However it is hardly ever discussed in relation to the neurodevelopmental disorders. Here we report on an 18-years-old female patient with 13.1 kb deletion of 8q24.3 fusing the 5'-portion of SCRIB with the 3'-portion of PUF60 and presenting with borderline intellectual disability, eye coloboma, short stature, scoliosis, heart defects and interestingly postnatal megalencephaly, in contrast to microcephaly, which is usually associated with 8q24.3 deletion (Verheij syndrome). Using next generation sequencing we mapped the breakpoints at nucleotide resolution and showed that the deletion preserved the reading frame. In contrast to the laborious techniques previously used for the precise mapping of deletion breakpoints, our approach identified an accurate interval very rapidly. We demonstrated the expression of the PUF60-SCRIB fusion gene in patient's cells and suggest that the fusion transcript might be a cause of the atypical clinical presentation.

A Novel SLC6A8 Mutation in a Large Family with X-Linked Intellectual Disability: Clinical and Proton Magnetic Resonance Spectroscopy Data of Both Hemizygous Males and Heterozygous Females.

X-linked creatine transport (CRTR) deficiency, caused by mutations in the SLC6A8 gene, leads to intellectual disability, speech delay, epilepsy, and autistic behavior in hemizygous males. Additional diagnostic features are depleted brain creatine levels and increased creatine/creatinine ratio (cr/crn) in urine. In heterozygous females the phenotype is highly variable and diagnostic hallmarks might be inconclusive. This survey aims to explore the intrafamilial variability of clinical and brain proton Magnetic Resonance Spectroscopy (MRS) findings in males and females with CRTR deficiency. X-chromosome exome sequencing identified a novel missense mutation in the SLC6A8 gene (p.G351R) in a large family with X-linked intellectual disability. Detailed clinical investigations including neuropsychological assessment, measurement of in vivo brain creatine concentrations using quantitative MRS, and analyses of creatine metabolites in urine were performed in five clinically affected family members including three heterozygous females and one hemizygous male confirming the diagnosis of CRTR deficiency. The severe phenotype of the hemizygous male was accompanied by most distinct aberrations of brain creatine concentrations (-83% in gray and -79% in white matter of age-matched normal controls) and urinary creatine/creatinine ratio. In contrast, the heterozygous females showed varying albeit generally milder phenotypes with less severe brain creatine (-50% to -33% in gray and -45% to none in white matter) and biochemical urine abnormalities. An intrafamilial correlation between female phenotype, brain creatine depletion, and urinary creatine abnormalities was observed. The combination of powerful new technologies like exome-next-generation sequencing with thorough systematic evaluation of patients will further expand the clinical spectrum of neurometabolic diseases.

Mirror-image asymmetry in monozygotic twins with kabuki syndrome.

Kabuki syndrome (OMIM 147920) is a rare disorder characterised by moderate intellectual disability, growth retardation, microcephaly and characteristic facial dysmorphic features which comprise long palpebral fissures, eversion of the lateral third of the eyelids and arched eyebrows with lateral sparseness. Mutations in MLL2 are the most frequent cause of this disorder. More than 100 MLL2 point mutations have been reported, but large intragenic deletions comprising one or more exons have not yet been identified. We report on a pair of monozygotic twin brothers in whom a deletion of 2 neighbouring exons was detected. The twins had the characteristic facial features of Kabuki syndrome, and they suffered from microcephaly, cleft lip and palate and congenital heart disease. Cleft lip and palate were left-sided in the first twin and right-sided in the second twin, i.e. they represented a mirror-image asymmetry. The intragenic deletion in these brothers broadens the spectrum of MLL2 mutations, and they provide a rare example of mirror-image asymmetry of congenital malformations in monozygotic twins.

Absence of Yq microdeletions in infertile men.

Microdeletions of the long arm of the Y chromosome (Yq) were described in men with idiopathic azoo- or oligozoospermia and seem to cause impairment of spermatogenesis. Deletion frequencies differ considerably among selected infertile men. The aim of this study was to investigate the prevalence of Yq microdeletions in patients with idiopathic infertility. Men with azoospermia or oligozoospermia resulting from endocrine or obstructive causes or with a constitutional cytogenetic anomaly were excluded. Ninety-seven patients presenting at infertility centers in Leipzig and Zurich were included in the study. Sixty-four (66%) of them were severely oligozoospermic (sperm concentrations < 5 x 10(6)/mL) and 33 (36%) were azoospermic. A sequence-tagged site (STS) PCR strategy was applied for the microdeletion screening. Thirteen STS markers spanning the whole euchromatic region of Yq were used. No Y-chromosomal microdeletion could be detected in these 97 infertile men. This result suggests a much lower Yq deletion frequency than previously thought, even among strictly selected patients with idiopathic azoo- or oligozoospermia.