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Coffin-Lowry Syndrome, also referred to as CLS, is a genetic disorder that can result in severe physiological and cognitive deficits [1]. CLS follows a X-Linked inheritance pattern, with semidominant effects [1]. The syndrome is often associated with growth defects, psychomotor difficulties, and abnormalities of the skeleton, facial features, and digits [1]. CLS can present in a wide range of severities, with different clinical signs and symptoms for each individual affected [1]. CLS is estimated to have a prevalence rate of anywhere between 1:50,000 to 1:100,000 [2]. It is also estimated that 70-80% of CLS cases are due to sporadic mutations, with no family history of the disease [1].

History

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Timeline of CLS

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1966-- Coffin et al. study published describing one family exhibiting the first documented cases of CLS [3].

1971-- Lowry et al. article published describing a differing CLS-affected family [3].

1975-- Dr. Temtamy determined the findings by Coffin and Lowry described the same syndrome, and coined Coffin-Lowry Syndrome [3].

1988-- Hanauer et al. study published mapping the CLS causative gene locus to the X chromosome thus confirming that the condition followed X-linked inheritance [3].

1996-- Trivier et al. first identified and isolated the protein product associated with the CLS causal gene subsequently named RSK2 [3].

Signs and Symptoms

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A variable range of phenotypes can be seen, from relatively normal to very severe. Most males who inherit a mutant allele show a clinically more severe case than seen in women. Women can show clinical symptoms when heterozygous and homozygous for the mutant allele. This variable combined with semidominant inheritance pattern creates the variety of phenotypes seen in women.

Cardiovascular

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14% of affected males and 5% of affected females have cardiovascular disease. Symptoms include abnormalities of the tricuspid, mitral and aortic valves, short chordae tendineae, unexplained heart failure, and dilation of the aorta and pulmonary artery. Cardiac problems contribute to the premature death of some patients.[4]

Craniofacial

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Patients with Coffin-Lowry present with very distinct facial features. The eyes are very wide-set and the opening between eyelids is narrow and slants downward. The nose is broad with a thicker than normal area between the nostrils. The mouth is large with very full lips that turn upward. The ears are large and low-set. The skull in general is thickened with prominent eye brow ridges and large sinuses. [5][6]

Neurological/Cognitive

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Symptoms generally present more commonly and more severely in males. Deafness, schizophrenia, and convulsions present themselves within the first year of life, with females more severely affected by schizophrenia[5]. Drop attacks start as early as four years of age with the mean age of onset around 8.5 years. Drop attacks occur when a stimulus triggers an electromyographic silence in the lower limbs causing the individual to collapse. The individual does not lose consciousness during these episodes. Epileptic seizures affect 5% of individuals[4]. Some autistic-like behaviors can be seen such as general anxiety, temper tantrums, hampered speech, emotional outbursts, and aggressive or self-injurious behaviors[6].

Skeletal

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Scoliosis and spinal stenosis are very prominent in all patients with the inervertebral spaces severely narrowed. Most patients experience delayed bone growth and brittle bones, along with pigeon chest or tunnel chest. Patients are in the 5th percentile for height[5][6]. The hands are short in length with tapered fingers and tufting on the distal phalanges. Hands are also soft with very elastic skin. Nails are hyperconvex and short[4][5][6].

Genetics

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Inheritance: X-Linked

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Males have an X and a Y chromosome, while women have two X chromosomes, each of which has an equal opportunity of passing along to their offspring. Each parent (mom and dad) is capable of passing on a single X chromosome to their offspring. Each daughter then will have the father's X chromosome and a 50% chance of inheriting each of the mother's chromosomes. If the couple were to have a son, the father would pass on the Y chromosome and the son would have a 50% chance of inheriting either X chromosome from mom. Males who inherit the affected allele will present with CLS, because they have no protection from a second X chromosome. However, women present with a more complicated case, they can have both an affected allele and a normal allele creating the opportunity for carriers. Heterozygous women have also shown to present mild symptoms of CLS, displaying the semi dominance ability of the syndrome [1]. CLS will undoubtable appear in women who receive 2 mutant alleles, following the same prognosis as males [1]. A majority of boys with Coffin–Lowry syndrome have no history of the condition in their families. These cases are caused by new mutations in the RPS6KA3 gene (de novo mutations) [1]. A new mutation means that neither parent has the altered gene, but the affected individual could pass it on to his children. (Already on article)

Gene: RPS6KA3

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Coffin-Lowry Syndrome is caused by mutations in a single gene called ribosomal protein S6 kinase A3 (RPS6KA3) [7]. This gene is located on the short arm of the X Chromosome, region 22, and on the second band (Xp22.2) [1]. The RPS6KA3 gene is comprised of 22 exons, and codes for a ribosomal S6 kinase (RSK), specifically RSK2 [8].

Protein: RSK2

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RSK2 is a serine/threonine protein kinase, primarily active in the Ras/MAPK signaling pathway [8]. The RSK2 protein is made of 740 amino acids and weighs 90 kDa [2]. There are four RSK proteins that make up an enzyme family called MAPKAP-K1 [1]. Each of these separate proteins are similar in function and shape but are each encoded by a different gene [1]. RSK proteins have significant cellular responsibilities, directly and indirectly affecting cell proliferation, differentiation, and apoptosis [9]. The highest catalytic activity of RSK2 is seen in areas of the brain where neural activity is its greatest [1]. These high activity level areas of the brain include the hippocampus, neocortex, and purkinje cells [1]. These brain areas have all been significantly linked to both cognitive functioning and learning in humans [2].

RSK2 is composed of two functional domains, one at each end of the protein, the N-terminus and the C-terminus [2]. Each of these domains has the kinase activity, with the ability to phosphorylate downstream proteins [2]. Between the two functional domains lie a linkage, which acts as a substrate for the PDK enzyme [2]. This PDK enzyme phosphorylates the RSK2 protein for activation [2]. Once activated the phosphorylated RSK2 can affect a large variety of substrates, translation factors, and apoptotic proteins [2]. The substrates known to be phosphorylated by RSK2 are GSK3, L1CAM, Ras GEF-Sos, IkB, and the p34cdc2-inhibitory kinase Myt1[2]. The translation factors and the apoptotic protein known to be phosphorylated by RSK2 are eEF2, eIF4B, and BAD [2]. Indirectly through the primary activated proteins, RSK2 also affects transcription factors in the cell nucleus [2]. These transcription factors include histones, SRF, CREB 1, ERα, and Nurr 77 [2]. There are an incredible amount of secondary interactions from the activation of RSK2, and the exact pathways of these interactions has not been described or completely understood [2].

Types of Mutations

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More than 140 mutations on the RPS6KA3 gene have been associated with Coffin-Lowry syndrome [1]. These mutations include missense mutations, nonsense mutations, deletions, insertions, and splicing errors [1]. Taking into account that most cases are de novo (new), the variety of different mutations is likely to grow over time. The 140 identified mutations show no grouping on the chromosome, with relatively even distribution across the 22 exons [1]. The result of these mutations typically leads to a loss of function truncated protein [1]. The non-functional proteins created by a mutation in the RPS6KA3 gene do not have the ability to phosphorylate the downstream molecules, causing a variety of effects.

Pathogenesis

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There is not much that is known about the deficits in Coffin-Lowry syndrome but it is thought that the RPS6KA3 protein has a role in the development of the nervous system[3]. Research has begun to show that the RPS6KA3 protein has a major impact on the biochemical pathway involving the CREB protein which plays a role in memory formation[3]. It has been found that the ERK/MAPK pathway is crucial for the development of memories and without the CREB protein being phosphorylated by ERK, cognitive defects are present[3]. This has led researchers to believe that the absence of CREB phosphorylation is a cause of the cognitive defects as cells from CLS patients were deficient in the phosphorylation of CREB[3]. There is data further supporting the absence of CREB phosphorylation as studies have shown that the CREB protein is phosphorylated by ERK which is in turn activated by the RPS6KA3 protein[3].

The mechanism as to how skeletal features are affected by the RPS6KA3 mutation is also unknown[3]. However, it is proposed that RPS6KA3 plays a similar role as the CREB protein cycle in the phosphorylation of the protein ATF4[10]. ATF4 is a protein that regulates the differentiation of osteoblasts into mature bone cells[10]. A study on CLS had used mice that were deficient in the RPS6KA3 protein yielded results that had decreased osteoblast function[10]. This study also found that ATF4 was an additional substrate for phosphorylation by the RPS6KA3 protein and although ATF4 has sites that are phosphorylated by other proteins, it nonetheless could play a role in the skeletal malformations seen in CLS[10].

Genotype/Phenotype Relationship

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Previous studies involving the mutated gene RPS6KA3, have been unable to establish a relationship between the gene, specific mutations, and the severity of the phenotype that is shown[3]. There are however, cases where there is a more mild phenotype in cases where the mutation was a missense mutation instead of a nonsense mutation[3]. Patients that were observed with this missense mutation exhibited mild mental retardation compared to patients with the nonsense mutation[3]. There is a great deal of intrafamilial variation seen in cases of Coffin-Lowry syndrome that have been studied and the data implies that to determine phenotypical expression, there are other factors such as the environment the patient is in and other genes that modify the protein product of RPS6KA3[3].

Diagnosis

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Clinical presentation

Clinical-based diagnostic screening for Coffin-Lowry syndrome can typically only be utilized for males patients exhibiting moderate to severe phenotypes[3]. The genetic condition's first clinical designation, mental retardation with osteocartiliginous anomolies[11], indicates the initial clinical tests and criteria first utilized to diagnose, characterize and identify the syndrome. Consequently, initial clinical indicators of CLS include a significantly low IQ score in addition to abnormalities in growth or physical features[11].

Classic male CLS characteristics include profound intellectual disabilities, characteristic craniofacial and appendage deformities, and a history of missing developmental milestones[3]. Characteristic CLS physical abnormalities of male patients typically become more distinguishable with age thus contributing to the difficulty of early diagnosis[4].

Radiography for CLS patients screens for structural indicators of the disorder including cranial hyperostosis, metacarpal pseudoepiphysis, and narrowed intervertebral spacing[12]. Due to the heterogeneity of radiographic findings associated with the syndrome, clinical radiology most commonly functions secondarily, as a confirmative tool for Coffin-Lowry candidates[4].

For female patients, clinical diagnostic techniques face unique difficulties due to the syndrome's characteristic gender-specific phenotypic heterogeneity specifically concerning the severity of physical or radiological abnormalities, intellectual capability, and developmental retardation[4]. Obesity and psychiatric illness have been indicated to occur significantly high frequency specifically for female CLS cases.

Molecular diagnostic tools

Due to the labor-intensive nature and expense associated with molecular genetic testing, such tools normally are used as secondary alternatives to clinical examinations in diagnostics. Circumstances necessitating the utilization of molecular diagnostic tools regarding Coffin-Lowry syndrome include for prenatal screening, CLS family genetic counseling, and for differential diagnosis[1]. The CLS phenotype presented in younger males may be confused with other syndromic forms of mental retardation such as ATR-X, BFL syndrome, Williams syndrome, Pitt-Hopkins syndrome, and FG syndrome[1]. In such cases, and also in cases of the heterogenous female carrier phenotype, of inconclusive clinical diagnoses, molecular diagnostic tests can only be implemented in order to differentially confirm, not rule out, a suspected CLS diagnosis[1][4].

Genetic testing

Genetic testing for Coffin-Lowry syndrome involves sequence analysis of RPS6KA3, the only known locus in which pathogenic variants implicate CLS, to scan candidate DNA for pathogenic variants[4]. RSK2 mutation screening used for CLS diagnostics requires systematically sequencing the PCR products containing all 22 exons and each intron-exon boundary present within human RPS6KA3[13]. This genetic screening method may not recognize certain types of mutations, specifically duplications and splice altering variants, thus results cannot be used to rule out the possibility of CLS[1]. Alternatively, positive sequence analysis results, indicating the presence of a pathogenic gene variant, can be used to definitively diagnose[1]. The significantly low percentage reported for the number of sequence analysis detected pathogenic variants compared to the total number of male CLS patients[1] researched could indicate evidence in support of CLS possessing locus heterogeneity[1] although, presently, no associative pathogenic variants in any other locus other than that of the RSK-2 gene have been discovered.

Western blot analysis

Western blot techniques has commonly been used in CLS diagnostics to characterize the RSK-2 tissue-specific expression patterns in CLS patients and quantify RSK-2 expression in order to identify mutated RSK-2 proteins thus provide diagnostic evidence of CLS at the protein level instead of the genomic level. Western blot analysis has proven effective in identifying the approximated 70% of pathogenic loss-of-function RPS6KA3 variants that lead to the loss or significant decrease of RSK-2 protein expression at the cellular level[1].

In vitro enzyme assay

RIbosomal S6 kinase enzymatic activity can be quantified using in vitro enzyme assay protocol for use a highly effective confirmative CLS diagnostic tool for male patients[1]. Significantly decreased RSK-2 enzyme activity have been observed in both cultured fibroblasts and transformed lymphoblasts purified from blood samples of CLS male patients possessing an identified pathogenic variant[4]. This may serve as a potential alternative molecular tool to genetic testing in differential confirming CLS diagnosis in males. Assays are particularly useful in diagnosing cases in which patients possess a pathogenic RPS6KA3 variant undetectable by sequence analysis[1][14] In vitro functional protein assays have high potential in CLS diagnostics due to the technology's ability to identify all pathogenic RSK-2 variants. This includes the approximately 30% of pathogenic variants containing missense mutations not affecting levels of RSK-2 expression, thus unidentifiable through western blotting, but instead codes for a functionally deficient version of the enzyme partially or completely lacking wild-type phosphotransferase activity[1][14].

Due to the cellular effects random X-inactivation, neither the western blot or in vitro protein assays techniques can function as effective methods for identifying heterozygous female CLS carriers[1]. Sequence analysis[4], more generally any genetic mutation analysis method[1], remain the most effective secondary diagnostic method of female CLS cases including when asymptomatic CLS carrier detection is necessary within genetic counseling as well as when required for differential diagnosis of CLS in females presenting a more severe, symptomatic form of the heterozygous phenotype[1].

Treatment and Management

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There is no known cure for CLS. Specific treatment is targeted towards each individual's symptoms.

Treatment

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Treatment is symptomatic and supportive and includes physical, speech therapy, and educational services[15]. Stimulus-induced drop attacks (SIDAs) are treated with medications such as valporate, clonazepam, or selective serotonin uptake inhibitors; individuals who experience frequent SIDAs may require use of a wheelchair and should be protected, if possible, from being startled[5]. Children and young adults who have CLS require early habilitation[3].

Management

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It is important for those who have CLS to receive periodic hearing, dental,vision, and cardiac examinations[5]. Patients should also monitor for progressive kyphoscoliosis. Sometimes a surgical corset or surgery may be useful in treating kyphoscoliosis[3]. Impaired hearing may be improved by hearing aids for a cochlear implant[3].

Genetic Counseling

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Approximately 70-80% have no family history of CLS, 20-30% have more than one affected family member[5]. Males who inherit the pathogenic variant will be affected; females who inherit the pathogenic variant will be carriers and at high risk for at least some developmental delay and mild physical signs of CLS. Prenatal and carrier testing are available for those who have the pathogenic variant identified in an affected family member[5]. Genetic testing is recommended for males with severe developmental delay, characteristic craiofacial and hand findings along with radiographic findings[6]. It should also be considered for females with similar but mild findings [6].

Prognosis

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Some patients have a shorter lifespan than unaffected individuals. Approximately 4.5% of females and 13.5% of males at the average age of 20.5 die from respiratory issues, progressive kyphoscoliosis, and cardiovascular complications.[6] Average life expectancy is 13 to 34 years, but there have been reported cases of individuals living to age 35 and older. [16] While there currently is no standard treatment for all patients with Coffin-Lowry Syndrome, patients who receive early intervention can have the same lifespan as unaffected individuals, through the assistance of different therapies and management of symptoms. [6]

Future Research

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Present research has yet to identify any correlation between the location or particular type of RPS6KA3 gene mutation and phenotype severity or symptomatic manifestations for patients. Future medical research projects on Coffin-Lowry syndrome are motivated towards identifying genotype:phenotype correlations in order to more develop more effective methods of diagnosing CLS, as well as for other syndromic forms of X-linked mental retardation, and towards developing a better medical understanding of the pathophysiology of CLS.

Community Resources

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The Coffin–Lowry Syndrome Foundation acts as a clearinghouse for information on Coffin–Lowry syndrome and hosts a forum for affected families. The family matching program facilitates community building and resource sharing for recent diagnoses.[6] (Already on Page)

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Category:Deficiencies of intracellular signaling peptides and proteins Category:Rare diseases Category:Syndromes


References

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  1. ^ a b c d e f g h i j k l m n o p q r s t u v w x y z aa ab ac ad ae Marques Pereira, Patricia; Schneider, Anne; Pannetier, Solange; Heron, Delphine; Hanauer, André (2016-11-15). "Coffin–Lowry syndrome". European Journal of Human Genetics. 18 (6): 627–633. doi:10.1038/ejhg.2009.189. ISSN 1018-4813. PMC 2987346. PMID 19888300.
  2. ^ a b c d e f g h i j k l m Zeniou-Meyer, M.; Gambino, F.; Ammar, Mohamed-Raafet; Humeau, Y.; Vitale, N. (2010-11-09). "The Coffin-Lowry Syndrome-Associated Protein rsk2 and Neurosecretion". Cellular and Molecular Neurobiology. 30 (8): 1401–1406. doi:10.1007/s10571-010-9578-9. ISSN 0272-4340.
  3. ^ a b c d e f g h i j k l m n o p q r s t Hanauer, A.; Young, I. D. (2002-10-01). "Coffin-Lowry syndrome: clinical and molecular features". Journal of Medical Genetics. 39 (10): 705–713. doi:10.1136/jmg.39.10.705. ISSN 1468-6244. PMC 1734994. PMID 12362025. Cite error: The named reference ":6" was defined multiple times with different content (see the help page).
  4. ^ a b c d e f g h i j Rogers, R. Curtis; Abidi, Fatima E. (1993-01-01). Pagon, Roberta A.; Adam, Margaret P.; Ardinger, Holly H.; Wallace, Stephanie E.; Amemiya, Anne; Bean, Lora JH; Bird, Thomas D.; Fong, Chin-To; Mefford, Heather C. (eds.). GeneReviews(®). Seattle (WA): University of Washington, Seattle. PMID 20301520.
  5. ^ a b c d e f g h Wasersprung, David; Sarnat, Haim (2006). "Coffin-Lowry Syndrome: Findings and dental treatment". Spec. Care Dentist. 26: 220–224. Cite error: The named reference ":4" was defined multiple times with different content (see the help page).
  6. ^ a b c d e f g h i "COFFIN-LOWRY SYNDROME". Ambry Genetics. Retrieved 2016-11-30. Cite error: The named reference ":5" was defined multiple times with different content (see the help page).
  7. ^ Reference, Genetics Home. "RPS6KA3 gene". Genetics Home Reference. Retrieved 2016-11-29.
  8. ^ a b Jacquot, S.; Merienne, K.; De Cesare, D.; Pannetier, S.; Mandel, J. L.; Sassone-Corsi, P.; Hanauer, A. (1998-12-01). "Mutation analysis of the RSK2 gene in Coffin-Lowry patients: extensive allelic heterogeneity and a high rate of de novo mutations". American Journal of Human Genetics. 63 (6): 1631–1640. doi:10.1086/302153. ISSN 0002-9297. PMC 1377634. PMID 9837815.
  9. ^ Reference, Genetics Home. "RPS6KA3 gene". Genetics Home Reference. Retrieved 2016-11-30.
  10. ^ a b c d Yang, Xiangli; Matsuda, Koichi; Bialek, Peter; Jacquot, Sylvie; Masuoka, Howard; Schinke, Thorsten; Li, Lingzhen; Brancorsini, Stefano; Sassone-Corsi, Paolo (2004). "ATF4 Is a Substrate of RSK2 and an Essential Regulator of Osteoblast Biology: Implication for Coffin-Lowry Syndrome". Cell. 117: 387–398.
  11. ^ a b Coffin, G.S.; Siris, Evelyn; Wegienka, Laurence (1966). "Mental Retardation with Osteocartilaginous Anomalies". Amer J Dis Child. 112: 205–213.
  12. ^ Kondoh, Tatsuro; Matsumoto, Tadashi; Ochi, Makoto; Sukegawa, Kazuko; Tusuji, Yoshiro (1998). "New radiological findings by magnetic resonance imaging examination of the brain in Coffin-Lowry syndrome". Human Genetics. 43. Nature Publishing Group: 59–61 – via Pubmed.
  13. ^ Delaunoy, J.P.; Dubos, A.; Pereira, M.P.; Hanauer, A. (2006). "Identification of novel mutations in the RSK2 gene (RPS6KA3) in patients with Coffin-Lowry syndrome". Clinical Genetics. 70: 161–166 – via Pubmed.
  14. ^ a b Zeniou, Maria; Pannetier, Solange; Fryns, Jean-Pierre; Hanauer, Andre (2002). "Unusual Splice-Site Mutations in the RSK2 Gene and Suggestion of Genetic Heterogeneity in Coffin-Lowry Syndrome". American Journal of Human Genetics. 70: 1421–1433 – via Pubmed Central.
  15. ^ "Coffin Lowry Syndrome -- American Academy of Neurology". patients.aan.com. Retrieved 2016-11-30.
  16. ^ Partington, M. W.; Mulley, J. C.; Sutherland, G. R.; Thode, A.; Turner, G. (1988-05-01). "A family with the Coffin Lowry syndrome revisited: Localization of CLS to Xp21-pter". American Journal of Medical Genetics. 30 (1–2): 509–521. doi:10.1002/ajmg.1320300153. ISSN 1096-8628.
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