Structural variation in Xq28: MECP2 duplications in 1% of patients with unexplained XLMR and in 2% of male patients with severe encephalopathy.

Duplications in Xq28 involving MECP2 have been described in patients with severe mental retardation, infantile hypotonia, progressive spasticity, and recurrent infections. However, it is not yet clear to what extent these and accompanying symptoms may vary. In addition, the frequency of Xq28 duplications including MECP2 has yet to be determined in patients with unexplained X-linked mental retardation and (fe)males with severe encephalopathy. In this study, we used multiplex ligation-dependent probe amplification to screen Xq28 including MECP2 for deletions and duplications in these patient cohorts. In the group of 283 patients with X-linked mental retardation, we identified three Xq28 duplications including MECP2, which suggests that approximately 1% of unexplained X-linked mental retardation may be caused by MECP2 duplications. In addition, we found three additional MECP2 duplications in 134 male patients with mental retardation and severe, mostly progressive, neurological symptoms, indicating that the mutation frequency could be as high as 2% in this group of patients. In 329 female patients, no Xq28 duplications were detected. In total, we assessed 13 male patients with a MECP2 duplication from six unrelated families. Moderate to severe mental retardation and childhood hypotonia was noted in all patients. The majority of the patients also presented with absent speech, seizures, and progressive spasticity as well as ataxia or an ataxic gait and cerebral atrophy, two previously unreported symptoms. We propose to implement DNA copy number testing for MECP2 in the current diagnostic testing in all males with moderate to severe mental retardation accompanied by (progressive) neurological symptoms.

Unique occurrence of Brachmann-de Lange syndrome in a fetus whose mother presented with a diffuse large B-cell lymphoma.

Brachmann-De Lange Syndrome (BDLS, MIM 122470) is a rare multiple congenital anomaly/mental retardation syndrome characterized by a variable phenotype including intrauterine fetal growth retardation, limb reduction and distinctive facial and skull features (low frontal hairline, synophrys, anteverted nostrils, long philtrum, downturned corners of the mouth, micro- and retrognathia, low-set ears and micro-/brachycephaly), as well as a significant psychological developmental delay. A proposed classification system for BDLS include a classic type with characteristic facial and skull changes, a mild type where similar changes may develop with time or may be partially expressed, and a third type including phenocopies, where phenotypic changes are casually related to chromosomal aneuploidies or teratogenic exposures. We report on a 22-week gestation fetus with BDLS, showing intrauterine fetal growth retardation, brachycephaly, micro-/retrognathia and monolateral single bone of the forearm, in a woman harboring diffuse large B-cell lymphoma. Meticulous family history was negative for malformations, syndromes, congenital anomalies or psychiatric disorders. There are very few reports of BDLS at early gestation, but to the best of our knowledge, this is the first case occurring simultaneously with a hematological neoplastic disease of the mother.

Trisomy 8q and partial trisomy 22 in a 43-year-old man with moderate intellectual disability, epilepsy and large cell non-Hodgkin lymphoma.

Partial trisomies are chromosome abnormalities resulting in a broad range of malformations depending on the size and location of the chromosomal rearrangement. Whereas diagnosis of these syndromes is usually made in early childhood, few descriptions exist about the clinical picture in adulthood. We report on a patient diagnosed at the age of 43 years with a 47,XY,+der(22)t(8;22)(q24.13;q11.21) karyotype and predominant clinical features of trisomy 8q. To our knowledge, this is the oldest patient described with a partial trisomy 8. The patient presented with moderate intellectual disability, a past history of epilepsy and facial anomalies. In addition, a large cell non-Hodgkin lymphoma was diagnosed in adulthood. Detailed breakpoint mapping by single nucleotide polymorphism (SNP) arrays showed that the derivative chromosome contains a full-length copy of the C-MYC oncogene. Given that trisomy 8q is the most frequent secondary chromosomal abnormality in hematological diseases, the possibility of a genetic predisposition for these disorders in patients with 8q duplication is raised.

Survival up to age 10 years in a patient with partial duplication 6q: case report and review of the literature.

Partial duplication of chromosome 6q has been recognized as a distinct dysmorphic syndrome with severe psychomotor and growth retardation, typical craniofacial features including microcephaly and microstomia, neck webbing, congenital contractures, and variable internal malformations. Most patients have died in the first year of life. We describe the clinical features and disease course in a boy with a duplication of 6q23.3-qter who lived up to the age of 10 years and discuss similarities with other patients.

Mutations in the JARID1C gene, which is involved in transcriptional regulation and chromatin remodeling, cause X-linked mental retardation.

In families with nonsyndromic X-linked mental retardation (NS-XLMR), >30% of mutations seem to cluster on proximal Xp and in the pericentric region. In a systematic screen of brain-expressed genes from this region in 210 families with XLMR, we identified seven different mutations in JARID1C, including one frameshift mutation and two nonsense mutations that introduce premature stop codons, as well as four missense mutations that alter evolutionarily conserved amino acids. In two of these families, expression studies revealed the almost complete absence of the mutated JARID1C transcript, suggesting that the phenotype in these families results from functional loss of the JARID1C protein. JARID1C (Jumonji AT-rich interactive domain 1C), formerly known as "SMCX," is highly similar to the Y-chromosomal gene JARID1D/SMCY, which encodes the H-Y antigen. The JARID1C protein belongs to the highly conserved ARID protein family. It contains several DNA-binding motifs that link it to transcriptional regulation and chromatin remodeling, processes that are defective in various other forms of mental retardation. Our results suggest that JARID1C mutations are a relatively common cause of XLMR and that this gene might play an important role in human brain function.

Allelic heterogeneity in the COH1 gene explains clinical variability in Cohen syndrome.

Cohen syndrome is a rare autosomal recessive disorder with a variable clinical picture mainly characterized by developmental delay, mental retardation, microcephaly, typical facial dysmorphism, progressive pigmentary retinopathy, severe myopia, and intermittent neutropenia. A Cohen syndrome locus was mapped to chromosome 8q22 in Finnish patients, and, recently, mutations in the gene COH1 were reported in patients with Cohen syndrome from Finland and other parts of northern and western Europe. Here, we describe clinical and molecular findings in 20 patients with Cohen syndrome from 12 families, originating from Brazil, Germany, Lebanon, Oman, Poland, and Turkey. All patients were homozygous or compound heterozygous for mutations in COH1. We identified a total of 17 novel mutations, mostly resulting in premature termination codons. The clinical presentation was highly variable. Developmental delay of varying degree, early-onset myopia, joint laxity, and facial dysmorphism were the only features present in all patients; however, retinopathy at school age, microcephaly, and neutropenia are not requisite symptoms of Cohen syndrome. The identification of novel mutations in COH1 in an ethnically diverse group of patients demonstrates extensive allelic heterogeneity and explains the intriguing clinical variability in Cohen syndrome.

Holoprosencephaly, bilateral cleft lip and palate and ectrodactyly: another case and follow up.

We describe a male patient with lobar holoprosencephaly, ectrodactyly, and cleft lip/palate, a syndrome which has been seen previously in only six patients. In addition, our patient developed hypernatraemia, which has been described in three patients before.

Multicolor chromosomal bar coding characterizes a de novo interstitial deletion (5)(q33.3q35.2) in a child with multiple congenital malformations.

We describe a boy with multiple congenital anomalies including a complex heart defect, club feet, adducted thumbs, and facial dysmorphic features. He died at the age of 2 months following cardiac surgery. G-banding analysis identified an abnormal chromosome 5q suspected to be an interstitial deletion (5)(q33q35). Breakpoints of the deleted segment were confirmed as del(5)(q33.3q35) by multicolor fluorescence in situ hybridization (FISH) using two sets of combinatorially labeled band specific YAC clones. Findings are discussed in view of previously published cases.

Agnathia-otocephaly complex: report of three cases with involvement of two different Carnegie stages.

Three fetuses with agnathia-otocephaly complex representing different degrees of embryonic maldevelopment are reported. The study of the three cases and of the anterior embryonic disc supports the concept that an altered embryologic development might have taken place at Carnegie stages 10 (embryonic days 22 or 23) and 11 (embryonic days 23-26). Karyotypic abnormalities and aberrant gene expression of sonic hedgehog and paired-related homeobox genes are discussed as the cytogenetic and molecular basis of agnathia-otocephaly complex.

The novel Rho-GTPase activating gene MEGAP/ srGAP3 has a putative role in severe mental retardation.

In the last few years, several genes involved in X-specific mental retardation (MR) have been identified by using genetic analysis. Although it is likely that additional genes responsible for idiopathic MR are also localized on the autosomes, cloning and characterization of such genes have been elusive so far. Here, we report the isolation of a previously uncharacterized gene, MEGAP, which is disrupted and functionally inactivated by a translocation breakpoint in a patient who shares some characteristic clinical features, such as hypotonia and severe MR, with the 3p(-) syndrome. By fluorescence in situ hybridization and loss of heterozygosity analysis, we demonstrated that this gene resides on chromosome 3p25 and is deleted in 3p(-) patients that present MR. MEGAP/srGAP3 mRNA is predominantly and highly expressed in fetal and adult brain, specifically in the neurons of the hippocampus and cortex, structures known to play a pivotal role in higher cognitive function, learning, and memory. We describe several MEGAP/srGAP3 transcript isoforms and show that MEGAP/srGAP3a and -b represent functional GTPase-activating proteins (GAP) by an in vitro GAP assay. MEGAP/srGAP3 has recently been shown to be part of the Slit-Robo pathway regulating neuronal migration and axonal branching, highlighting the important role of MEGAP/srGAP3 in mental development. We propose that haploinsufficiency of MEGAP/srGAP3 leads to the abnormal development of neuronal structures that are important for normal cognitive function.

Study of 30 patients with unexplained developmental delay and dysmorphic features or congenital abnormalities using conventional cytogenetics and multiplex FISH telomere (M-TEL) integrity assay.

Cryptic subtelomeric chromosome rearrangements are a major cause of mild to severe mental retardation pointing out the necessity of sensitive screening techniques to detect such aberrations among affected patients. In this prospective study a group of 30 patients with unexplained developmental retardation and dysmorphic features or congenital abnormalities were analysed using the recently published multiplex FISH telomere (M-TEL) integrity assay in combination with conventional G-banding analysis. The patients were selected by one or more of the following criteria defined by de Vries et al.: (a) family history with two or more affected individuals, (b) prenatal onset growth retardation, (c) postnatal growth abnormalities, (d) facial dysmorphic features, (e) non-facial dysmorphism and congenital abnormalities. In addition, we included two patients who met these criteria and revealed questionable chromosome regions requiring further clarification. In four patients (13.3%) cryptic chromosome aberrations were successfully determined by the M-TEL integrity assay and in two patients with abnormal chromosome regions intrachromosomal aberrations were characterized by targetted FISH experiments. Our results accentuate the requirement of strict selection criteria prior to patient testing with the M-TEL integrity assay. Another essential precondition is high-quality banding analysis to identify structural abnormal chromosomes. The detection of familial balanced translocation carriers in 50% of the cases emphasizes the significance of such an integrated approach for genetic counselling and prenatal diagnosis.