Arts Syndrome
Arjan PM de Brouwer, PhD and John Christodoulou, MBBS, PhD.
Author Information and AffiliationsInitial Posting: October 21, 2008; Last Update: March 22, 2018.
Estimated reading time: 15 minutes
Summary
Clinical characteristics.
Arts syndrome, which is part of the spectrum of PRPS1-related disorders, is characterized by profound congenital sensorineural hearing impairment, early-onset hypotonia, delayed motor development, mild to moderate intellectual disability, ataxia, and increased risk of infection, all of which – with the exception of optic atrophy – present before age two years. Signs of peripheral neuropathy develop during early childhood. Twelve of 15 boys from the two Dutch families reported with Arts syndrome died before age six years of complications of infection. Carrier females can show late-onset (age >20 years) hearing impairment and other findings.
Diagnosis/testing.
The diagnosis of Arts syndrome can be established in a male proband with absent ribose-phosphate pyrophosphokinase 1 (PRS-I) enzyme activity in erythrocytes, or significantly lower PRS-1 enzyme activity in fibroblasts than in controls, or identification of a hemizygous pathogenic variant in PRPS1 by molecular genetic testing. The diagnosis of Arts syndrome can be established in a female proband with suggestive clinical features and identification of a heterozygous pathogenic variant in PRPS1 by molecular genetic testing.
Management.
Treatment of manifestations: Educational program tailored to individual needs. Sensorineural hearing loss has been treated with cochlear implantation with good results. Ataxia and visual impairment from optic atrophy are treated in a routine manner.
Prevention of secondary complications: Routine immunizations against common childhood infections and annual influenza immunization.
Surveillance: Regular neuropsychological, audiologic, and ophthalmologic examinations.
Genetic counseling.
Arts syndrome is inherited in an X-linked manner. If the mother is a carrier, the chance of transmitting the PRPS1 pathogenic variant in each pregnancy is 50%. Males who inherit the pathogenic variant will be affected; females who inherit the pathogenic variant will be carriers and may or may not be mildly affected. Males with Arts syndrome have not reproduced. Carrier testing for at-risk relatives and prenatal testing for a pregnancy at increased risk are possible if the pathogenic variant in the family is known.
Diagnosis
Formal diagnostic criteria for Arts syndrome have not been established.
Suggestive Findings
Arts syndrome, part of the spectrum of PRPS1-related disorders, should be suspected in
a male
proband with the following clinical and laboratory features.
Clinical features
Laboratory features
Serum uric acid concentration lower than average (0.13-0.16 mmol/L), although still within the normal range (i.e., 0.12-0.35 mmol/L) [
de Brouwer et al 2007]
Note: (1) Serum uric acid concentration is not zero because PRS-II, which has the same enzyme activity as PRS-I, is active in tissues such as liver, which consequently will result in purine nucleotide synthesis and uric acid production. (2) However, a low/normal serum uric acid concentration may be helpful in ruling out a diagnosis of
PRS superactivity, in which serum uric acid concentration is usually high.
Purine
analysis in urine
Absent/low hypoxanthine on analysis of purines in the urine
When individuals with Arts syndrome are on a low-purine diet, the uric acid to creatinine ratio in urine may also tend to be at the lower end of normal, but not zero.
Concentrations of other purines in urine within the normal range
Arts syndrome should be suspected in
a female
proband with late-onset (age >20 years) sensorineural hearing impairment.
Establishing the Diagnosis
Male proband. The diagnosis of Arts syndrome is established in a male proband with ANY of the following:
Female proband. The diagnosis of Arts syndrome is usually established in a female proband with late-onset (age >20 years) sensorineural hearing impairment and identification of a heterozygous pathogenic variant in PRPS1 by molecular genetic testing (see ).
Molecular genetic testing approaches can include a combination of gene-targeted testing (single-gene testing, multigene panel) and comprehensive
genomic testing (exome sequencing, genome sequencing) depending on the phenotype.
Gene-targeted testing requires that the clinician determine which gene(s) are likely involved, whereas genomic testing does not. Because the phenotype of Arts syndrome is broad, individuals with the distinctive findings described in Suggestive Findings are likely to be diagnosed using gene-targeted testing (see Option 1), whereas those in whom the diagnosis of Arts syndrome has not been considered are more likely to be diagnosed using genomic testing (see Option 2).
Option 1
When the phenotypic and laboratory findings suggest the diagnosis of Arts syndrome molecular genetic testing approaches can include single-gene testing or use of a multigene panel:
A multigene panel that includes
PRPS1 and other genes of interest (see
Differential Diagnosis) may be considered. Note: (1) The genes included in the panel and the diagnostic
sensitivity of the testing used for each
gene vary by laboratory and are likely to change over time. (2) Some multigene panels may include genes not associated with the condition discussed in this
GeneReview; thus, clinicians need to determine which multigene panel is most likely to identify the genetic cause of the condition while limiting identification of variants of
uncertain significance and pathogenic variants in genes that do not explain the underlying
phenotype. (3) In some laboratories, panel options may include a custom laboratory-designed panel and/or custom phenotype-focused
exome analysis that includes genes specified by the clinician. (4) Methods used in a panel may include
sequence analysis,
deletion/duplication analysis, and/or other non-sequencing-based tests.
For an introduction to multigene panels click
here. More detailed information for clinicians ordering genetic tests can be found
here.
Option 2
When the diagnosis of Arts syndrome is not considered because an individual has atypical phenotypic features, comprehensive genomic testing (which does not require the clinician to determine which gene[s] are likely involved) is the best option. Exome sequencing is the most commonly used genomic testing method; genome sequencing is also possible.
For an introduction to comprehensive genomic testing click here. More detailed information for clinicians ordering genomic testing can be found here.
Table 1.
Molecular Genetic Testing Used in Arts Syndrome
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| Gene 1 | Method | Proportion of Probands with a Pathogenic Variant 2 Detectable by Method |
|---|
|
PRPS1
| Sequence analysis 3 | 4 families 4 |
| Gene-targeted deletion/duplication analysis 5 | Unknown 6 |
- 1.
- 2.
- 3.
- 4.
- 5.
Gene-targeted deletion/duplication analysis detects intragenic deletions or duplications. Methods used may include a range of techniques such as quantitative PCR, long-range PCR, multiplex ligation-dependent probe amplification (MLPA), and a gene-targeted microarray designed to detect single-exon deletions or duplications.
- 6.
Clinical Characteristics
Clinical Description
Arts syndrome is characterized by intellectual disability, early-onset hypotonia, ataxia, delayed motor development, profound congenital sensorineural hearing impairment, and progressive optic atrophy [Arts et al 1993, de Brouwer et al 2007].
At birth these symptoms can be present in various combinations. All symptoms except for the visual impairment become apparent in the first two years of life. Visual impairment usually becomes obvious after age two years.
Delayed motor nerve conduction velocities and an electromyography suggestive of denervation develop during early childhood and are consistent with clinical findings that suggest peripheral neuropathy.
Affected males usually have mild to moderate intellectual disability; however, cognitive abilities can be difficult to assess in the presence of combined visual and hearing impairment.
Liability to infections, especially upper-respiratory tract infections, resulted in death before age six years in 12 of 15 boys from the two Dutch families reported with Arts syndrome. During infection, the slowly progressive muscle weakness is punctuated by acute deterioration in muscle strength, which may result in respiratory failure requiring mechanical ventilation.
Heterozygous females can show isolated and/or milder manifestations, most notably late-onset (age >20 years) hearing impairment. Ataxia (in 2 females), hypotonia (1 female), and hyperreflexia (1 female) have been reported as well [Arts et al 1993].
MRI shows no recognizable abnormalities (e.g., reduction of white matter in the brain, which would indicate demyelination) [de Brouwer et al 2007].
Sural nerve biopsy in a boy age five years with Arts syndrome from the original Dutch family showed a loss of myelinated fibers, but no signs of demyelination or axonal degeneration [Arts et al 1993]. Sural nerve biopsy of a boy age two years from the Australian family, who had absent lower-limb deep tendon reflexes and nerve conduction studies indicative of peripheral neuropathy, showed mild paranodal demyelination indicative of peripheral neuropathy [de Brouwer et al 2007].
Autopsy of one individual who died at age five and a half years revealed complete absence of myelinated axons in the posterior columns of the spinal cord, although their number and appearance were normal in the other tracts [Arts et al 1993]. A number of dorsal root nerves showed the same abnormalities as posterior columns. No abnormalities were seen in the brain stem or in the gray and white matter of the cerebral and cerebellar hemispheres.
Genotype-Phenotype Correlations
Computer-assisted molecular modeling showed that pathogenic variants causing Arts syndrome and CMTX5 disturb the ATP binding site of PRS-I.
Pathogenic variants that result in PRS superactivity disturb either one or both allosteric sites that are involved in the inhibition of PRS-I enzyme activity.
Pathogenic variants that lead to DFNX1 nonsyndromic hearing loss and deafness (DFN2) either disturb local stability of PRS-I or moderately affect interactions in the trimer interface.
Penetrance
Penetrance in males is complete.
Management
Evaluations Following Initial Diagnosis
To establish the extent of disease and needs in an individual diagnosed with Arts syndrome, the evaluations summarized in this section (if not performed as part of the evaluation that led to the diagnosis) are recommended:
Neurologic evaluation for manifestations of hypotonia, ataxia, presence/absence of tendon reflexes
Audiometry for evidence of hearing loss
Eye examination for evidence of optic atrophy
Assessment of intellectual abilities
Analysis of the family
pedigree for other possible affected individuals and
carrier females
Consultation with a clinical geneticist and/or genetic counselor
Treatment of Manifestations
Intellectual disability. An individualized educational support program tailored to the individual’s needs and based on assessment of cognitive abilities should be provided.
Ataxia. See Hereditary Ataxias, Management.
Sensorineural hearing loss. See Hereditary Hearing Loss and Deafness Overview, Management. Cochlear implantation in the two affected Australian males was associated with improved communication skills.
Optic atrophy. No treatment is available.
Prevention of Secondary Complications
Because of immune system compromise in males with Arts syndrome, the following are recommended:
An annual influenza immunization
Routine immunizations against other common childhood infections (e.g., measles, mumps)
Surveillance
Cognitive impairment appears to be non-progressive, but repeat neuropsychologic assessments are recommended to help guide educational support programs.
Although the sensorineural deafness appears to be static (albeit very severe), regular audiologic assessment is recommended so that educational support can be optimized.
Visual impairment appears to be progressive; thus, regular evaluation by an ophthalmologist is recommended.
Therapies Under Investigation
Dietary S-adenosylmethionine (SAM) supplementation could theoretically alleviate some of the symptoms of Arts syndrome by providing an oral source of purine nucleotide precursor that is not phosphoribosyl pyrophosphate dependent. Furthermore, SAM is known to cross the blood-brain barrier. An adult with HPRT deficiency has been reported to benefit neurologically from SAM administration without untoward side effects [Glick 2006].
In an open-label clinical trial of SAM in two Australian brothers (ages 14 and 13 in 2010) with Arts syndrome [J Christodoulou et al, unpublished data; approved by the ethics and drug committees, Children's Hospital at Westmead, Sydney, Australia], oral SAM supplementation was set at 30 mg/kg/day. The brothers appear to have had significant benefit from this therapy based on decreased number of hospitalizations and stabilization of nocturnal BIPAP requirements; however, slight deterioration in their vision was noted. Eventually, they died at ages 19 and 18 years of respiratory failure associated with a severe lower respiratory tract infection.
Mildly affected carrier females from families with Arts syndrome may also benefit from SAM supplementation in their diet, although this remains to be tested.
Search ClinicalTrials.gov in the US and EU Clinical Trials Register in Europe for access to information on clinical studies for a wide range of diseases and conditions.
Genetic Counseling
Genetic counseling is the process of providing individuals and families with
information on the nature, mode(s) of inheritance, and implications of genetic disorders to help them
make informed medical and personal decisions. The following section deals with genetic
risk assessment and the use of family history and genetic testing to clarify genetic
status for family members; it is not meant to address all personal, cultural, or
ethical issues that may arise or to substitute for consultation with a genetics
professional. —ED.
Mode of Inheritance
Arts syndrome is inherited in an X-linked manner.
Risk to Family Members
Parents of a male proband
The father of an affected male will not have the disorder nor will he be
hemizygous for the
PRPS1 pathogenic variant; therefore, he does not require further evaluation/testing.
In a family with more than one affected individual, the mother of an affected male is an
obligate heterozygote (
carrier). Note: If a woman has more than one affected child and no other affected relatives and if the
PRPS1 pathogenic variant cannot be detected in her leukocyte DNA, she most likely has
germline mosaicism.
If a male is the only affected family member (i.e., a
simplex case), the mother may be a
heterozygote (
carrier) or the affected male may have a
de novo
PRPS1 pathogenic variant, in which case the mother is not a carrier. The frequency of
de novo pathogenic variants is not known.
Parents of a female proband
A female
proband may have inherited the
PRPS1 pathogenic variant from either her mother or her father, or the pathogenic variant may be
de novo. Of note, to date no male with Arts syndrome has been known to reproduce.
Detailed evaluation of the parents and review of the extended family history may help distinguish probands with a
de novo pathogenic variant from those with an inherited pathogenic variant. Molecular genetic testing of the mother (and possibly the father, or subsequently the father) can determine if the pathogenic variant was inherited.
Sibs of a male proband. The risk to sibs depends on the genetic status of the mother:
If the mother of the
proband has a
PRPS1 pathogenic variant, the chance of transmitting it in each pregnancy is 50%. Males who inherit the pathogenic variant will be affected; females who inherit the pathogenic variant will be heterozygotes (carriers) and may or may not be mildly affected.
If the
proband represents a
simplex case (i.e., a single occurrence in a family) and if the
PRPS1 pathogenic variant cannot be detected in the leukocyte DNA of the mother, the risk to sibs is slightly greater than that of the general population (though still <1%) because of the possibility of maternal
germline mosaicism.
Sibs of a female proband. The risk to sibs depends on the genetic status of the parents:
If the mother of the
proband has a
PRPS1 pathogenic variant, the chance of transmitting it in each pregnancy is 50%. Males who inherit the pathogenic variant will be affected; females who inherit the pathogenic variant will be heterozygotes (carriers) and may or may not be mildly affected.
If the
proband represents a
simplex case (i.e., a single occurrence in a family) and if the
PRPS1 pathogenic variant cannot be detected in the leukocyte DNA of either parent, the risk to sibs is slightly greater than that of the general population (though still <1%) because of the possibility of parental
germline mosaicism.
Offspring of a male proband. Males with Arts syndrome do not reproduce.
Offspring of a female proband. Women with a PRPS1 pathogenic variant have a 50% chance of transmitting the pathogenic variant to each child:
Females who inherit the
pathogenic variant will be heterozygotes (carriers) and may or may not be mildly affected.
Other family members. The proband's maternal aunts may be at risk of being heterozygous (and asymptomatic or symptomatic) and the aunts' offspring, depending on their sex, may be at risk of being hemizygous (and affected) or heterozygous.
Heterozygote Detection
Molecular genetic testing of at-risk female relatives to determine their genetic status is most informative if the pathogenic variant has been identified in the proband.
Note: (1) Females who are heterozygous (carriers) for this X-linked disorder may develop clinical findings related to the disorder, most notably late-onset (age >20 years) hearing impairment; ataxia, hypotonia, and hyperreflexia have been reported as well [Arts et al 1993]. (2) Identification of female heterozygotes requires either (a) prior identification of the PRPS1 pathogenic variant in the family or, (b) if an affected male is not available for testing, molecular genetic testing first by sequence analysis, and if no pathogenic variant is identified, by gene-targeted deletion/duplication analysis.
Resources
GeneReviews staff has selected the following disease-specific and/or umbrella
support organizations and/or registries for the benefit of individuals with this disorder
and their families. GeneReviews is not responsible for the information provided by other
organizations. For information on selection criteria, click here.
American Association on Intellectual and Developmental Disabilities (AAIDD)
Phone: 202-387-1968
Fax: 202-387-2193
American Society for Deaf Children
Phone: 800-942-2732 (ASDC)
Email: info@deafchildren.org
CDC - Developmental Disabilities
Phone: 800-CDC-INFO
Email: cdcinfo@cdc.gov
National Ataxia Foundation
Phone: 763-553-0020
Fax: 763-553-0167
Email: naf@ataxia.org
National Eye Institute
Phone: 301-496-5248
Email: 2020@nei.nih.gov
Molecular Genetics
Information in the Molecular Genetics and OMIM tables may differ from that elsewhere in the GeneReview: tables may contain more recent information. —ED.
Table A.
Arts Syndrome: Genes and Databases
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Data are compiled from the following standard references: gene from
HGNC;
chromosome locus from
OMIM;
protein from UniProt.
For a description of databases (Locus Specific, HGMD, ClinVar) to which links are provided, click
here.
Gene structure.
PRPS1 consists of seven exons that code for ribose-phosphate pyrophosphokinase 1 (PRS-I), a protein of 318 amino acid residues. Only one isoform has been described for PRS-I. For a detailed summary of gene and protein information, see Table A, Gene.
Pathogenic variants. To date, only four pathogenic variants have been identified (see ), resulting in missense changes at the protein level.
Table 3.
PRPS1 Pathogenic Variants Discussed in This GeneReview
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| DNA Nucleotide Change | Predicted Protein Change | Reference Sequences |
|---|
| c.398A>C | p.Gln133Pro |
NM_002764.3
NP_002755.1
|
| c.455T>C | p.Leu152Pro |
| c.830A > C | p.Gln277Pro |
| c.367C>G | p.His123Asp |
Variants listed in the table have been provided by the authors. GeneReviews staff have not independently verified the classification of variants.
GeneReviews follows the standard naming conventions of the Human Genome Variation Society (varnomen.hgvs.org). See Quick Reference for an explanation of nomenclature.
Normal gene product. PRS-I catalyzes the synthesis of phosphoribosyl pyrophosphate (PRPP) from ATP and ribose-5-phosphate. PRPP is essential for the de novo synthesis of purine, pyrimidine, and pyridine nucleotides. For purine synthesis, PRPP is utilized as a substrate for PRPP amidotransferase, which is the first step in the de novo purine synthesis pathway, producing purine nucleotides such as ATP and GTP, and serves specifically as the rate-limiting reaction for purine nucleotide synthesis in vivo. PRPP is also essential for pyrimidine nucleotide synthesis, where it acts as cofactor for uridine monophosphate synthetase, which converts orotic acid into UMP, the precursor of other pyrimidine nucleotides including UTP, CTP, and TTP. Finally, PRPP is utilized for pyridine nucleotide synthesis by nicotinate phosphoribosyl transferase and nicotinamide phosphoribosyl transferase, which add a ribonucleotide moiety to nicotinic acid and nicotinamide respectively, which in turn are converted into the important cofactor NAD.
Apart from de novo synthesis of purine, pyrimidine, and pyridine nucleotides, PRPP is also essential for the salvage of purine bases by hypoxanthine guanine phosphoribosyl transferase and adenine phosphoribosyl transferase. This mechanism ensures efficient reutilization of purine bases and nucleosides, since de novo purine nucleotide synthesis using PRPP as the substrate requires a total of seven moles of ATP for generation of each mole of nucleotide, whereas salvage requires only one mole of ATP, for the synthesis of PRPP.
Abnormal gene product.
In silico molecular modeling predicted that both missense variants would result in a loss of PRS-I activity, which was accordingly demonstrated by in vitro PRS enzyme assays in erythrocytes and fibroblasts from the Australian family and fibroblasts from the Dutch kindred. This was reflected by undetectable urine hypoxanthine and reduced plasma uric acid levels in the two affected individuals from the Australian family.
Chapter Notes
Acknowledgments
The authors are grateful to the families of the Dutch and Australian patients for providing samples used for biochemical and molecular analyses over a number of years.
Author History
Arjan PM de Brouwer, PhD (2008-present)
John Chrstodoulou, MBBS, PhD (2008-present)
John A Duley, PhD; University of Queensland (2008-2018)
Revision History
22 March 2018 (sw) Comprehensive update posted live
29 March 2011 (cd) Revision: edits to Differential Diagnosis
4 January 2011 (cd) Revision: changes to Therapies Under Investigation
18 November 2010 (me) Comprehensive update posted live
21 October 2008 (me) Review posted live
3 June 2008 (apmb) Original submission
References
Literature Cited
Arts WF, Loonen MC, Sengers RC, Slooff JL. X-linked ataxia, weakness, deafness, and loss of vision in early childhood with a fatal course.
Ann Neurol. 1993;33:535–9. [
PubMed: 8498830]
de Brouwer AP, Williams KL, Duley JA, van Kuilenburg AB, Nabuurs SB, Egmont-Petersen M, Lugtenberg D, Zoetekouw L, Banning MJ, Roeffen M, Hamel BC, Weaving L, Ouvrier RA, Donald JA, Wevers RA, Christodoulou J, van Bokhoven H. Arts syndrome is caused by loss-of-function mutations in PRPS1.
Am J Hum Genet. 2007;81:507–18. [
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