An unexpected presentation of very severe hypertriglyceridemia in a boy with Coffin-Lowry syndrome: a case report

BACKGROUND

Coffin-Lowry syndrome (CLS) is a rare X-linked condition with intellectual disability, growth retardation, characteristic facies and skeletal anomalies. To date, hypertriglyceridemia has not been reported in literature to be associated with CLS.

CASE PRESENTATION

Herein, we report a case of very severe hypertriglyceridemia 32 mmol/L (2834 mg/dL) detected incidentally at three months old in an otherwise well boy born late preterm with intrauterine growth restriction, when he presented with lipaemic plasma. He was later diagnosed with CLS. No pathogenic mutations were found for hypertriglyceridemia, and no secondary causes could explain his very severe hypertriglyceridemia.

CONCLUSIONS

The very severe hypertriglyceridemia in this case may appear to be a serious presentation of an unrecognised clinical feature of CLS, further expanding its phenotype.

Coffin-Lowry Syndrome Induced by RPS6KA3 Gene Variation in China: A Case Report in Twins

Background and objectives: Coffin-Lowry Syndrome (CLS), a rare neurodegenerative disorder, is mainly diagnosed based on clinical manifestations and molecular analyses. In total, about 20 cases of CLS have been reported in China. Here, we report two cases of CLS in identical twin brothers and examine their potential causative mutations. Methods: The Trio mode was used in this analysis, i.e., DNA from the proband and his parents was sequenced. Furthermore, DNA from the proband’s twin brother was used for confirmation. Results: A hemizygous variation was detected in the 11th exon of the RPS6KA3 gene, c.898C>T (p.R300*) of the proband, and the same site variation was detected in his identical twin brother; however, the mutation was not detected in his parents. Conclusions: The RPS6KA3 gene mutation c.898C>T (p.R300*) is the causative factor of familial CLS. The variant detected was reported for the first time in the Chinese population. Additionally, by analyzing the previous literature, we were able to summarize the phenotypic and genetic characteristics of GLS in China.

Short Bones, Renal Stones, and Diagnostic Moans: Hypercalcemia in a Girl Found to Have Coffin-Lowry Syndrome

Pathogenic variants in RPS6KA3 are associated with Coffin-Lowry syndrome (CLS), an X-linked semidominant disorder characterized by intellectual disability, stimulus-induced drop attacks, distinctive facial features, progressive kyphoscoliosis, and digit anomalies in hemizygous males. Heterozygous females may also have features of CLS; however, there can be considerable phenotypic variation, often attributed to ratios of X-inactivation in various tissue types. Although skeletal anomalies and short stature are hallmarks of CLS, hypercalcemia has not been reported. Here we describe a 30-month-old girl with gross motor delays, short stature, dysmorphic features, bilateral duplicated renal collecting systems, and no family history of hypercalcemia who required multiple admissions for idiopathic hypercalcemia necessitating bisphosphonate infusions at 12.5 and 15 months of age. A maternally inherited likely-pathogenic variant in RPS6KA3 was identified by trio exome sequencing, consistent with the diagnosis of CLS in the proband and her mother. Maternal history was notable only for decreased height compared to first-degree relatives, bilateral genu valgum, and a bicornuate uterus; she was later found to also have a partially duplicated left renal collecting system. Subsequent X-inactivation studies in blood aligned with the phenotypic variation between mother and daughter. Although hypercalcemia is not a reported feature in CLS, there is evidence of interrupted osteoblast differentiation, providing a potential mechanism for hypercalcemia in this genetic condition. The hypercalcemia in this case may represent a severe presentation of an unrecognized clinical feature in CLS that resolves with age. This case further highlights the intrafamilial phenotypic variation of CLS among females, suggesting X-inactivation as the underlying mechanism, and demonstrates the value of exome sequencing in patients for whom a genetic disorder is highly suspected but not identified despite thorough evaluation.

A familial case of Coffin-Lowry syndrome caused by RPS6KA3 C.898C>T mutation associated with multiple abnormal brain imaging findings

Coffin-Lowry syndrome (CLS) is a rare X linked mental retardation syndrome characterised by severe psychomotor and growth retardation, distinct facial phenotype, and progressive skeletal malformations. It is caused by mutations in the RPS6KA3 gene located at Xp22.2. In this report we describe a family with CLS consists of three affected males, and two affected females, arising from c.898C>T mutation in RPS6KA3 gene. A 6 year-old, and a 3 year-old boy both had distinct clinical features of Coffin-Lowry syndrome; severe mental and motor retardation, microcephaly, prominent forehead, hypertelorism, large mouth, large ears, large soft hands, puffy tapered fingers, and pectus carinatum. In addition, they had multiple abnormal brain MRI findings. Other siblings presented with a mild and variable phenotype.

Defective synaptic transmission and structure in the dentate gyrus and selective fear memory impairment in the Rsk2 mutant mouse model of Coffin-Lowry syndrome

The Coffin-Lowry syndrome (CLS) is a syndromic form of intellectual disability caused by loss-of-function of the RSK2 serine/threonine kinase encoded by the rsk2 gene. Rsk2 knockout mice, a murine model of CLS, exhibit spatial learning and memory impairments, yet the underlying neural mechanisms are unknown. In the current study, we examined the performance of Rsk2 knockout mice in cued, trace and contextual fear memory paradigms and identified selective deficits in the consolidation and reconsolidation of hippocampal-dependent fear memories as task difficulty and hippocampal demand increase. Electrophysiological, biochemical and electron microscopy analyses were carried out in the dentate gyrus of the hippocampus to explore potential alterations in neuronal functions and structure. In vivo and in vitro electrophysiology revealed impaired synaptic transmission, decreased network excitability and reduced AMPA and NMDA conductance in Rsk2 knockout mice. In the absence of RSK2, standard measures of short-term and long-term potentiation (LTP) were normal, however LTP-induced CREB phosphorylation and expression of the transcription factors EGR1/ZIF268 were reduced and that of the scaffolding protein SHANK3 was blocked, indicating impaired activity-dependent gene regulation. At the structural level, the density of perforated and non-perforated synapses and of multiple spine boutons was not altered, however, a clear enlargement of spine neck width and post-synaptic densities indicates altered synapse ultrastructure. These findings show that RSK2 loss-of-function is associated in the dentate gyrus with multi-level alterations that encompass modifications of glutamate receptor channel properties, synaptic transmission, plasticity-associated gene expression and spine morphology, providing novel insights into the mechanisms contributing to cognitive impairments in CLS.

The role of genetics in the establishment and maintenance of the epigenome

Epigenetic mechanisms play an important role in gene regulation during development. DNA methylation, which is probably the most important and best-studied epigenetic mechanism, can be abnormally regulated in common pathologies, but the origin of altered DNA methylation remains unknown. Recent research suggests that these epigenetic alterations could depend, at least in part, on genetic mutations or polymorphisms in DNA methyltransferases and certain genes encoding enzymes of the one-carbon metabolism pathway. Indeed, the de novo methyltransferase 3B (DNMT3B) has been recently found to be mutated in several types of cancer and in the immunodeficiency, centromeric region instability and facial anomalies syndrome (ICF), in which these mutations could be related to the loss of global DNA methylation. In addition, mutations in glycine-N-methyltransferase (GNMT) could be associated with a higher risk of hepatocellular carcinoma and liver disease due to an unbalanced S-adenosylmethionine (SAM)/S-adenosylhomocysteine (SAH) ratio, which leads to aberrant methylation reactions. Also, genetic variants of chromatin remodeling proteins and histone tail modifiers are involved in genetic disorders like α thalassemia X-linked mental retardation syndrome, CHARGE syndrome, Cockayne syndrome, Rett syndrome, systemic lupus erythematous, Rubinstein-Taybi syndrome, Coffin-Lowry syndrome, Sotos syndrome, and facioescapulohumeral syndrome, among others. Here, we review the potential genetic alterations with a possible role on epigenetic factors and discuss their contribution to human disease.

Applying and testing the conveniently optimized enzyme mismatch cleavage method to clinical DNA diagnosis

Establishing a simple and effective mutation screening method is one of the most compelling problems with applying genetic diagnosis to clinical use. Because there is no reliable and inexpensive screening system, amplifying by PCR and performing direct sequencing of every coding exon is the gold standard strategy even today. However, this approach is expensive and time consuming, especially when gene size or sample number is large. Previously, we developed CEL nuclease mediated heteroduplex incision with polyacrylamide gel electrophoresis and silver staining (CHIPS) as an ideal simple mutation screening system constructed with only conventional apparatuses and commercially available reagents. In this study, we evaluated the utility of CHIPS technology for genetic diagnosis in clinical practice by applying this system to screening for the COL2A1, WRN and RPS6KA3 mutations in newly diagnosed patients with Stickler syndrome (autosomal dominant inheritance), Werner syndrome (autosomal recessive inheritance) and Coffin-Lowry syndrome (X-linked inheritance), respectively. In all three genes, CHIPS detected all DNA variations including disease causative mutations within a day. Direct sequencing of all coding exons of these genes confirmed 100% sensitivity and specificity. We demonstrate high sensitivity, high cost performance and reliability of this simple system, with compatibility to all inheritance modes. Because of its low technology, CHIPS is ready to use and potentially disseminate to any laboratories in the world.

A novel mutation in the RPS6KA3 gene in a patient with Coffin-Lowry syndrome

Coffin-Lowry syndrome is an X-linked disorder characterized by mental retardation, characteristic facial features, skeletal abnormalities, and tapering fingers. Herein we report a novel missense mutation in exon 7 at codon 180 in the RPS6KA3 gene in a boy with Coffin-Lowry syndrome.

The first large duplication of the RSK2 gene identified in a Coffin-Lowry syndrome patient

Heterogeneous mutations in the X-linked gene RPS6KA3, encoding the protein kinase RSK2, are responsible for Coffin-Lowry Syndrome. Here we have further studied a male patient with a highly suggestive clinical diagnosis of CLS but in whom no mutation was found by exon sequencing. Western blot analysis revealed a protein much larger than the normal expected size. Sequencing of the RSK2 cDNA, showed the presence of an in-frame tandem duplication of exons 17-20. The mutated RSK2 protein was found to be inactive in an in-vitro kinase assay. This event, which was the result of a homologous unequal recombination between Alu sequences, is the first reported large duplication of the RPS6KA3 gene. Our finding provides further evidence that immunoblot analysis, or a molecular assay capable to detect large genomic mutational events, is essential for patients with a highly suggestive CLS clinical diagnosis but remaining without mutation after exon sequencing.

Altered neurodevelopment associated with mutations of RSK2: a morphometric MRI study of Coffin-Lowry syndrome

Coffin-Lowry syndrome (CLS) is a rare form of X-linked mental retardation caused by mutations of the RSK2 gene, associated with cognitive impairment and skeletal malformations. We conducted the first morphometric study of CLS brain morphology by comparing brain volumes from two CLS families with healthy controls. Individuals with CLS consistently showed markedly reduced total brain volume. Cerebellum and hippocampus volumes were particularly impacted by CLS and may be associated with specific interfamilial RSK2 mutations. We provide preliminary evidence that the magnitude of hippocampus volume deviation from that of controls may predict general cognitive outcome in CLS.

Mutations in the RSK2(RPS6KA3) gene cause Coffin-Lowry syndrome and nonsyndromic X-linked mental retardation

We describe three families with X-linked mental retardation, two with a deletion of a single amino acid and one with a missense mutation in the proximal domain of the RSK2(RPS6KA3) (ribosomal protein S6 kinase, 90 kDa, polypeptide 3) protein similar to mutations found in Coffin-Lowry syndrome (CLS). In two families, the clinical diagnosis had been nonsyndromic X-linked mental retardation. In the third family, although CLS had been suspected, the clinical features were atypical and the degree of intellectual disability much less than expected. These families show that strict reliance on classical clinical criteria for mutation testing may result in a missed diagnosis. A less targeted screening approach to mutation testing is advocated.

Recruitment and activation of RSK2 by HIV-1 Tat

The transcriptional activity of the integrated HIV provirus is dependent on the chromatin organization of the viral promoter and the transactivator Tat. Tat recruits the cellular pTEFb complex and interacts with several chromatin-modifying enzymes, including the histone acetyltransferases p300 and PCAF. Here, we examined the interaction of Tat with activation-dependent histone kinases, including the p90 ribosomal S6 kinase 2 (RSK2). Dominant-negative RSK2 and treatment with a small-molecule inhibitor of RSK2 kinase activity inhibited the transcriptional activity of Tat, indicating that RSK2 is important for Tat function. Reconstitution of RSK2 in cells from subjects with a genetic defect in RSK2 expression (Coffin-Lowry syndrome) enhanced Tat transactivation. Tat interacted with RSK2 and activated RSK2 kinase activity in cells. Both properties were lost in a mutant Tat protein (F38A) that is deficient in HIV transactivation. Our data identify a novel reciprocal regulation of Tat and RSK2 function, which might serve to induce early changes in the chromatin organization of the HIV LTR.

Protein nutrition as therapy for a genetic disorder of bone?

Bone formation is controlled by a network of transcription factors and signaling molecules. In this issue, , studying the role of the transcription factor ATF4 in a new mouse model of neurofibromatosis type I skeletal defects, demonstrate striking effects of changing dietary protein on bone formation abnormalities.

ATF4 mediation of NF1 functions in osteoblast reveals a nutritional basis for congenital skeletal dysplasiae

The transcription factor ATF4 enhances bone formation by favoring amino acid import and collagen synthesis in osteoblasts, a function requiring its phosphorylation by RSK2, the kinase inactivated in Coffin-Lowry Syndrome. Here, we show that in contrast, RSK2 activity, ATF4-dependent collagen synthesis, and bone formation are increased in mice lacking neurofibromin in osteoblasts (Nf1(ob)(-/-) mice). Independently of RSK2, ATF4 phosphorylation by PKA is enhanced in Nf1(ob)(-/-) mice, thereby increasing Rankl expression, osteoclast differentiation, and bone resorption. In agreement with ATF4 function in amino acid transport, a low-protein diet decreased bone protein synthesis and normalized bone formation and bone mass in Nf1(ob)(-/-) mice without affecting other organ weight, while a high-protein diet overcame Atf4(-/-) and Rsk2(-/-) mice developmental defects, perinatal lethality, and low bone mass. By showing that ATF4-dependent skeletal dysplasiae are treatable by dietary manipulations, this study reveals a molecular connection between nutrition and skeletal development.

Deletion of the Coffin-Lowry syndrome gene Rsk2 in mice is associated with impaired spatial learning and reduced control of exploratory behavior

Coffin-Lowry Syndrome (CLS) is an X-linked syndromic form of mental retardation associated with skeletal abnormalities. It is caused by mutations of the Rsk2 gene, which encodes a growth factor regulated kinase. Gene deletion studies in mice have shown an essential role for the Rsk2 gene in osteoblast differentiation and function, establishing a causal link between Rsk2 deficiency and skeletal abnormalities of CLS. Although analyses in mice have revealed prominent expression of Rsk2 in brain structures that are essential for learning and memory, evidence at the behavioral level for an involvement of Rsk2 in cognitive function is still lacking. Here, we have examined Rsk2-deficient mice in two extensive batteries of behavioral tests, which were conducted independently in two laboratories in Zurich (Switzerland) and Orsay (France). Despite the known reduction of bone mass, all parameters of motor function were normal, confirming the suitability of Rsk2-deficient mice for behavioral testing. Rsk2-deficient mice showed a mild impairment of spatial working memory, delayed acquisition of a spatial reference memory task and long-term spatial memory deficits. In contrast, associative and recognition memory, as well as the habituation of exploratory activity were normal. Our studies also revealed mild signs of disinhibition in exploratory activity, as well as a difficulty to adapt to new test environments, which likely contributed to the learning impairments displayed by Rsk2-deficient mice. The observed behavioral changes are in line with observations made in other mouse models of human mental retardation and support a role of Rsk2 in cognitive functions.

Identification of novel mutations in the RSK2 gene (RPS6KA3) in patients with Coffin-Lowry syndrome

The Coffin-Lowry syndrome (CLS) is a rare X-linked semidominant syndrome characterized by severe psychomotor retardation, facial dysmorphism, digit abnormalities and progressive skeletal deformations. CLS is caused by mutations in a gene located in Xp22.2, RPS6KA3. This gene encodes for a growth factor-regulated serine/threonine protein kinase, RSK2 (ribosomal S6 kinase 2), acting in the Ras-mitogen-activated protein kinase signaling pathway. Mutations in the RPS6KA3 gene are extremely heterogeneous and lead to premature termination of translation and/or to loss of phosphotransferase activity of the RSK2 protein. Screening for RSK2 mutations is essential in most cases to confirm the diagnosis as well as for genetic counseling. Here we present 44 novel mutations in RSK2 causing CLS. The overall number of CLS mutations reported now is 128. Thirty-three percent of mutations are missense mutations, 15% nonsense mutations, 20% splicing errors and 29% short deletion or insertion events. Only four large deletions have so far been found. They are distributed throughout the RPS6KA3 gene, and the majority has been found in a single family. This study further confirms the high rate of new mutations at the RSK2 locus. It is important to consider the possibility of mosaicism when providing genetic counseling in CLS families.

p90 ribosomal S6 kinase 2 exerts a tonic brake on G protein-coupled receptor signaling

G protein-coupled receptors (GPCRs) are essential for normal central CNS function and represent the proximal site(s) of action for most neurotransmitters and many therapeutic drugs, including typical and atypical antipsychotic drugs. Similarly, protein kinases mediate many of the downstream actions for both ionotropic and metabotropic receptors. We report here that genetic deletion of p90 ribosomal S6 kinase 2 (RSK2) potentiates GPCR signaling. Initial studies of 5-hydroxytryptamine (5-HT)(2A) receptor signaling in fibroblasts obtained from RSK2 wild-type (+/+) and knockout (-/-) mice showed that 5-HT(2A) receptor-mediated phosphoinositide hydrolysis and both basal and 5-HT-stimulated extracellular signal-regulated kinase 1/2 phosphorylation are augmented in RSK2 knockout fibroblasts. Endogenous signaling by other GPCRs, including P2Y-purinergic, PAR-1-thrombinergic, beta1-adrenergic, and bradykinin-B receptors, was also potentiated in RSK2-deficient fibroblasts. Importantly, reintroduction of RSK2 into RSK2-/- fibroblasts normalized signaling, thus demonstrating that RSK2 apparently modulates GPCR signaling by exerting a "tonic brake" on GPCR signal transduction. Our results imply the existence of a novel pathway regulating GPCR signaling, modulated by downstream members of the extracellular signal-related kinase/mitogen-activated protein kinase cascade. The loss of RSK2 activity in humans leads to Coffin-Lowry syndrome, which is manifested by mental retardation, growth deficits, skeletal deformations, and psychosis. Because RSK2-inactivating mutations in humans lead to Coffin-Lowry syndrome, our results imply that alterations in GPCR signaling may account for some of its clinical manifestations.

A novelRSK2 (RPS6KA3) gene mutation associated with abnormal brain MRI findings in a family with Coffin–Lowry syndrome

Coffin-Lowry syndrome (CLS) is an X-linked mental retardation syndrome caused by defects in the RSK2 gene. We have identified a CLS family with four patients in two generations. The patients in this family, a mother and her three children (a male and two females), all have severe mental retardation with the typical CLS phenotype. In addition, brain MRI studies on the three siblings revealed abnormalities in deep subcortical white matter, thinning of the corpus callosum, hypoplastic cerebellar vermis, and asymmetry of the lateral ventricles. The degree of severity of the MRI findings correlated with the severity of mental retardation in the patients. Extensive mutation screening was performed on the entire RSK2 gene in this family. Twenty-two exons including the intron/exon junctions were amplified by PCR and subsequently sequenced on both strands. A novel mutation, a two-nucleotide insertion (298 ins TG), was identified. The insertion creates a stop codon at codon 100, resulting in a 99 amino acid truncated RSK2 protein. All patients tested have the same mutation, and no other mutation could be found in the RSK2 gene from the proband. The mutation was confirmed by PCR/RFLP. X-chromosome inactivation assay on the female patients revealed significant skewing toward inactivation of the normal RSK2 allele. Thus, this novel mutation is likely to be responsible for the unusual clinical presentation in this family, which includes full phenotypic expression in females and unique brain MRI abnormalities. The pathological function of the mutation and genotype/phenotype correlation between the mutation and this unusual clinical presentation await further clarification.

Neuroplasticity in children

Research in the field of neurosciences and genetics has given us great insight into the understanding of learning and behavior and changes in the brain in response to experience. It is seen that brain is dynamically changing throughout life and is capable of learning at any time. Critical periods of neuroplasticity for various streams of development are also better understood. Technological advances in non invasive imaging techniques and advances in molecular genetics have helped us understand the basis of many developmental disorders which may help in planning effective intervention strategies.

Essential role of RSK2 in c-Fos-dependent osteosarcoma development

Inactivation of the growth factor-regulated S6 kinase RSK2 causes Coffin-Lowry syndrome in humans, an X-linked mental retardation condition associated with progressive skeletal abnormalities. Here we show that mice lacking RSK2 develop a progressive skeletal disease, osteopenia due to impaired osteoblast function and normal osteoclast differentiation. The phenotype is associated with decreased expression of Phex, an endopeptidase regulating bone mineralization. This defect is probably not mediated by RSK2-dependent phosphorylation of c-Fos on serine 362 in the C-terminus. However, in the absence of RSK2, c-Fos-dependent osteosarcoma formation is impaired. The lack of c-Fos phosphorylation leads to reduced c-Fos protein levels, which are thought to be responsible for decreased proliferation and increased apoptosis of transformed osteoblasts. Therefore, RSK2-dependent stabilization of c-Fos is essential for osteosarcoma formation in mice and may also be important for human osteosarcomas.

RSK2 gene mutations in Coffin-Lowry syndrome with drop episodes

Coffin-Lowry syndrome is an X-linked mental retardation disorder with dysmorphism caused by mutation of the ribosomal S6 kinase (RSK2) gene. Coffin-Lowry syndrome patients can experience unusual drop episodes whereby an abrupt loss of muscle tone and falling down can be induced by sudden, unexpected tactile or auditory stimuli. We detected a C913T (R305X) mutation in a female Coffin-Lowry syndrome patient with drop episodes. All mutations in our patient and those previously reported in patients with drop episodes result in premature truncation of the RSK2 protein in the N-terminal kinase domain or upstream of this domain.

Intronic L1 insertion and F268S, novel mutations in RPS6KA3 (RSK2) causing Coffin-Lowry syndrome

Two novel mutations of the ribosomal S6 kinase 2 gene (also known as RSK2) have been identified in two unrelated patients with Coffin-Lowry syndrome. The first mutation consists of a de novo insertion of a 5'-truncated LINE-1 element at position -8 of intron 3, which leads to a skipping of exon 4, leading to a shift of the reading frame and a premature stop codon. The L1 fragment (2800 bp) showed a rearrangement with a small deletion, a partial inversion of the ORF 2, flanked by short direct repeats which duplicate the acceptor splice site. However, cDNA analysis of the patient shows that both sites are apparently not functional. The second family showed the nucleotide change 803T>C in exon 10, resulting in the F268S mutation. This mutation was detected in two monozygotic twin patients and in their mother, who was mildly affected. The patients fulfill the clinical criteria of the syndrome, and therefore the mutation provides further support for the importance of phenylalanine at position 268, which is highly conserved in the protein kinase domain of many serine-threonine protein kinases.

Delineation of the mechanisms of aberrant splicing caused by two unusual intronic mutations in the RSK2 gene involved in Coffin-Lowry syndrome

Coffin-Lowry syndrome (CLS) is caused by mutations in the RSK2 gene encoding a protein kinase of the Ras signalling pathway. We have studied two point mutations which cause aberrant splicing but do not concern the invariant GT or AG nucleotides of splice sites. The first, an A-->G transition at position +3 of the 5' splice site of exon 6, results in vivo and in vitro in exon skipping and premature translation termination. The natural 5' splice site, although intrinsically weak, is not transactivated under normal conditions. Consequently, replacement of an A/U by a G/U base pairing with U1 snRNA reduces its strength below a critical threshold. The second mutation, an A-->G transition 11 nt upstream of exon 5, creates a new AG near the natural 3' splice site. In vitro this synthetic 3' AG is used exclusively by the splicing machinery. In vivo this splicing event is also observed, but is underestimated because the resulting RSK2 mRNA contains premature stop codons which trigger the nonsense-mediated decay process. We show that a particular mechanism is involved in the aberrant splicing of exon 5, implying involvement of the natural 3' AG during the first catalytic step and the new 3' AG during the second step. Thus, our results explain how these mutations cause severe forms of CLS.

Cardiomyopathy in Coffin-Lowry syndrome

Coffin-Lowry syndrome (CLS) is a rare but well-documented X-linked disorder characterized by small size, developmental delay/mental retardation, and characteristic facial and skeletal findings in affected males. The phenotype in affected females is far more variable and can include developmental differences, obesity, and characteristic facial and skeletal differences. Cardiac anomalies are reported in less than 20% of affected males, with cardiomyopathy being one of the rare but reported complications of this disorder. However, cardiomyopathy is not well characterized in CLS. Here, we report on a 14-year-old boy with physical and developmental findings consistent with CLS who presented with a relatively sudden onset of signs of congestive heart failure due to a restrictive cardiomyopathy; an endomyocardial biopsy demonstrated non-specific hypertrophic myocyte alterations consistent with cardiomyopathy. This is the first description of the histology and electron microscopy of cardiomyopathy in CLS.

Syndromes of disordered chromatin remodeling

Syndromes of disordered 'chromatin remodeling' are unique in medicine because they arise from a general deregulation of DNA transcription caused by mutations in genes encoding enzymes which mediate changes in chromatin structure. Chromatin is the packaged form of DNA in the eukaryotic cell. It consists almost entirely of repeating units, called nucleosomes, in which short segments of DNA are wrapped tightly around a disk-like structure comprising two subunits of each of the histone proteins H2A, H2B, H3 and H4. Histone proteins are covalently modified by a number of different adducts (i.e. acetylation and phosphorylation) that regulate the tightness of the DNA-histone interactions. Mutations in genes encoding enzymes that mediate chromatin structure can result in a loss of proper regulation of chromatin structure, which in turn can result in deregulation of gene transcription and inappropriate protein expression. In this review we present examples of representative genetic diseases that arise as a consequence of disordered chromatin remodeling. These include: alpha-thalassemia/mental retardation syndrome, X-linked (ATR-X); Rett syndrome (RS); immunodeficiency-centromeric instability-facial anomalies syndrome (ICF); Rubinstein-Taybi syndrome (RSTS); and Coffin-Lowry syndrome (CLS).

Postmortem findings in the Coffin-Lowry Syndrome

The Coffin-Lowry Syndrome (CLS) is a congenital disorder that can be recognized by retarded growth and development, the characteristic appearance of the face and hands, and often by the typical deformities of the back and chest; there are many other anomalies. The history of the syndrome is reviewed, noting the x-linked semidominant pattern of inheritance, and two autopsies are presented and compared with the three autopsy reports that have been published previously. The five young patients died at ages between 18 to 28 years of advancing pneumonia, aspiration of food into the trachea, or postoperative complications. There were lesions or abnormalities in the heart, brain, lungs, liver, skeleton, kidneys, intestines, and other organs. Molecular geneticists have located the CLS gene or Rsk-2 gene at Xp22.2 and demonstrated that it works by influencing the activation of other genes. The "monopolygenic" pattern may help to explain the large number of seemingly unrelated abnormalities that make up this syndrome.

A female with Coffin-Lowry syndrome and "cataplexy"

Coffin-Lowry syndrome (CLS) is an X-linked semidominant condition, caused by mutations in the gene encoding the ribosomal protein S6 kinase-2 (RSK-2), a growth factor regulating protein kinase, which is mapped to Xp 22.2. The syndrome is mainly seen in males. It is manifested by moderate to severe mental retardation and characteristic facial, hand and skeletal malformations. We present a female patient with fully manifested CLS, confirmed by molecular analysis, who experienced daily drop episodes, diagnosed as "cataplexy". The episodes were precipitated by emotional or auditory stimuli and were significantly reduced, by selective serotonine re-uptake inhibitors.

Ataxia telangiectasia mutated proteins, MAPKs, and RSK2 are involved in the phosphorylation of STAT3

Phosphorylation at Ser(727) is known to be required for complete activation of STAT3 by diverse stimuli including UV irradiation, but the kinase(s) responsible for phosphorylating STAT3 (Ser(727)) is still not well discerned. In the present study, we observed that activation of ATM is required for a UVA-stimulated increase in Ser(727) phosphorylation of STAT3 as well as in activation and phosphorylation of p90 ribosomal protein S6 kinases (RSKs). Moreover, UVA-stimulated activation of upstream kinases, such as c-Jun N-terminal kinases (JNKs) and ERKs, involved in mediating phosphorylation of RSKs and STAT3 was defective or delayed in ATM-deficient cells. Furthermore, we provide evidence that RSK2-deficient cells were defective for UV-induced Ser(727) phosphorylation of STAT3, and the defect was restored after ectopic expression of transfected full-length RSK2. In vitro experiments showed that active RSK2 and JNK1 induce the phosphorylation of STAT3 precipitates from immunoprecipitation but not from glutathione S-transferase (GST) pull-down. Interestingly, the GST fusion STAT3 proteins mixed together with STAT3 immunoprecipitates can be phosphorylated by JNK. However, the in vitro phosphorylation of STAT3 was reduced by the GST-STAT3 beta protein, a dominant negative form of STAT3. Taken together, our results demonstrate that the STAT3 phosphorylation at Ser(727) is triggered by active RSK2 or JNK1 in the presence of a downstream kinase or a cofactor, and thereby the intracellular phosphorylation process is stimulated through a signaling pathway involving ATM, MAPKs, RSK2, and an as yet unidentified kinase or cofactor. Additionally, RSK2-mediated phosphorylation of STAT3 (Ser(727)) was further determined to be required for basal and UVA-stimulated STAT3 transcriptional activities.

Expression analysis of RSK gene family members: the RSK2 gene, mutated in Coffin-Lowry syndrome, is prominently expressed in brain structures essential for cognitive function and learning

Coffin-Lowry syndrome (CLS) is characterized by cognitive impairment, characteristic facial and digital findings and skeletal anomalies. The gene implicated in CLS encodes RSK2, a serine/threonine kinase acting in the Ras/MAPK signalling pathway. In humans, RSK2 belongs to a family of four highly homologous proteins (RSK1-RSK4), encoded by distinct genes. RSK2 mutations in CLS patients are extremely heterogeneous. No consistent relationship between specific mutations and the severity of the disease or the expression of uncommon features has been established. Together, the data suggest an influence of environmental and/or other genetic components on the presentation of the disease. Obvious modifying genes include those encoding other RSK family members. In this study we have determined the expression of RSK1, 2 and 3 genes in various human tissues, during mouse embryogenesis and in mouse brain. The three RSK mRNAs were expressed in all human tissues and brain regions tested, supporting functional redundancy. However, tissue specific variations in levels suggest that they may also serve specific roles. The mouse Rsk3 gene was prominently expressed in the developing neural and sensory tissues, whereas Rsk1 gene expression was the strongest in various other tissues with high proliferative activity, suggesting distinct roles during development. In adult mouse brain, the highest levels of Rsk2 expression were observed in regions with high synaptic activity, including the neocortex, the hippocampus and Purkinje cells. These structures are essential components in cognitive function and learning. Based on the expression levels, our results suggest that in these areas, the Rsk1 and Rsk3 genes may not be able to fully compensate for a lack of Rsk2 function.

Molecular Genetics of Human Cognition

Our understanding of the molecular underpinnings of human cognition has been greatly aided by the convergent synergy of clinical, genetic, and signaling research. By identifying the mutated genes that give rise to syndromes of mental retardation or cognitive defects in patients, and by placing the associated gene products within signaling networks, researchers are piecing together how learning occurs and how memories are formed and sustained.

Coffin-Lowry syndrome: a 20-year follow-up and review of long-term outcomes

The Coffin-Lowry syndrome has become well established since the first report of affected patients by Coffin et al. [1966: Am J Dis Child 112:205-213]. Since that time over a hundred cases have been reported and the responsible gene has been identified. However, there remains a paucity of long-term follow-up information on older patients with which to counsel affected families about prognosis. There is also much to be learned about genotype-phenotype correlations. In 1982 we reported 12 patients (including carrier mothers) from eight families, one of whom had died about the time the paper was written. Recently, we have been able to obtain follow-up information on six of the affected patients and one of the carrier mothers. A number of important complications have occurred, including premature death, loss of ambulation, and quadriplegia. This paper updates the medical histories of our patients and summarizes the clinically important complications that have been reported in patients with Coffin-Lowry syndrome. There are few data on patients over the age of 30, and much more longer term follow-up is required.

A syndromic form of X-linked mental retardation: the Coffin-Lowry syndrome

Coffin-Lowry syndrome (CLS, OMIM 303600) is an X-linked inherited disorder characterised in male patients by growth and psychomotor retardation, hypotonia and progressive skeletal changes. Typically, male patients are of short stature and exhibit a characteristic coarse face with a prominent forehead, orbital hypertelorism, downslanting palpebral fissures, thick lips, a thick nasal septum with anteverted nares, and irregular or missing teeth. Their large and soft hands with lax skin and tapering fingers, are usually a strong diagnostic feature. Some patients present with additional complications including, sensorineural deafness, seizures, drop episodes and cardiac disease. There is some variability in the mental development of affected males, but most of the males who receive appropriate care appear to be moderately affected. A majority of carrier females have only minimal findings (mild facial coarsening, tapering fingers and obesity). Early diagnosis of CLS is essential for proper management, including survey of some specific complications already mentioned, and for genetic counselling. Establishing the diagnosis in very young children is often much more difficult than in older patients since physical characteristics are milder and not specific. Loss of function mutations in the gene encoding the growth-factor induced protein kinase ribosomal S6 kinase are responsible for CLS. A mutation has been detected in about 50% of patients with clinical features suggestive of CLS, and over 80 different mutations have so far been identified. They are distributed throughout the gene, the vast majority being unique to single families and a high proportion appear to be de novo events. Some missense mutations are associated with milder phenotypes. In one family, a missense mutation was associated solely with mild mental retardation and no other clinical feature.

CONCLUSION

Coffin-Lowry syndrome is a well characterised entity and a detailed clinical examination usually allows diagnosis. However, recognising it in very young children is often difficult since physical characteristics are mild and not specific. In addition, most cases are sporadic. Screening for ribosomal S6 kinase mutations is essential in most cases to confirm the diagnosis as well as for genetic counselling.

Cognitive function in Coffin-Lowry syndrome

Coffin-Lowry syndrome (CLS) is an X-linked disorder associated with mental retardation, distinctive facies and hands, hypotonia, and skeletal abnormalities. The syndrome results from mutations in the RSK2 gene located in Xp22.2. Although the syndrome has been elucidated clinically, few, if any, studies have focused on the cognitive deficits of the affected males or carrier females. The subjects of the present study were selected from two African-American families who have the same missense mutation (C340T) in RSK2. The subjects included six affected males, seven carrier females, three normal males and three non-carrier (normal) females. Normal family members served as contrast/comparison cohorts to control for socio-economic, sociocultural and genetic variables which would impinge on intellectual abilities. Analysis of cognitive function, as measured by the Stanford-Binet Intelligence Scale, 4th edn, demonstrated a distinct hierarchy of abilities from normal to carrier to affected patients. The mean composite IQs of the cohorts were 90.8, 65.0 and 43.2 for normal, carrier and affected individuals, respectively. These findings lend support to the clinical concept of negative intellectual effects in carriers of certain X-linked mental retardation conditions. X-inactivation studies showed that carrier females had mild to significant skewing. Normal females in the family did not demonstrate skewing. The correlation coefficient between IQ and X-inactivation status among carriers was not significant.