Supernumerary marker chromosome (1) of paternal origin and maternal uniparental disomy 1 in a developmentally delayed child

Uniparental isodisomy of chromosome 1 results in glycogen storage disease type III with profound growth retardation

Background

Glycogen storage disease type III (GSDIII) is caused by mutations of AGL gene with debranching enzyme deficiency. Patients with GSDIII manifest fasting hypoglycemia, hepatomegaly, hepatopathy, myopathy, and cardiomyopathy. We report on an 18‐year‐old boy with a profound growth retardation (<3 SD) besides typical clinical features of GSDIII, whereby endocrinological studies were negative.

Methods and Results

Molecular analysis of AGL gene revealed the homozygous reported variant c.3903_3904insA. Since discordant results from segregation studies showed the carrier status in one parent only, SNP array and short tandem repeats analyses were performed, revealing a paternal disomy of chromosome 1 (UPD1).

Conclusion

This study describes the first case of GSDIII resulting from UPD1. UPD can play an important role even in case of imprinted genes. DIRAS3 is a maternally imprinted tumor suppressor gene, located on chromosome 1p31, and implicated in growth and oncogenesis. It can be speculated that DIRAS3 overexpression might have a role in the severe short stature of our patient. The study emphasizes the importance of parental segregation analysis especially in patients with recessive conditions to look for specific genetic causes of disease and to estimate properly the risk of family recurrence.

Characterization of a de novo sSMC 17 detected in a girl with developmental delay and dysmorphic features

BACKGROUND

The majority of small supernumerary marker chromosome cases arise de novo and their frequency in newborns is 0.04%. We report on a girl with developmental delay and dysmorphic features with a non-mosaic de novo sSMC that originated from the pericentric region of q arm in chromosome 17.

CASE PRESENTATION

The girl presented with developmental delay, speech delay, myopia, mild muscle hypotonia, hypoplasia of orbicular muscle, poor concentration, and hyperactivity. Main dysmorphic features included: round face, microstomia, small chin, down-slanting palpebral fissures and small lobules of both ears. At present, her developmental abilities are still delayed for her chronological age but she is making evident progress with speech. A postnatal array comparative genomic hybridization showed a 2.31 Mb genomic gain indicating microduplication derived from pericentric regions q11.1 and q11.2 of chromosome 17. Additional conventional cytogenetic analysis from peripheral blood characterized the karyotype as 47,XX,+mar in a non-mosaic form. The location of microduplication was confirmed with fluorescence in situ hybridization.

CONCLUSION

The proband's microduplication encompassed approximately 40 annotated genes, several of which have been associated with phenotypic characteristics of the proband. This is the first report of sSMC 17 including this particular chromosomal region in non-mosaic form.

Small supernumerary marker chromosomes and their correlation with specific syndromes

A small supernumerary marker chromosome (sSMC) is a structurally abnormal chromosome. It is an additional chromosome smaller than one chromosome most often lacking a distinct banding pattern and is rarely identifiable by conventional banding cytogenetic analysis. The origin and composition of an sSMC is recognizable by molecular cytogenetic analysis. These sSMCs are seen in different shapes, including the ring, centric minute, and inverted duplication shapes. The effects of sSMCs on the phenotype depend on factors such as size, genetic content, and the level of the mosaicism. The presence of an sSMC causes partial tris- or tetrasomy, and 70% of the sSMC carriers are clinically normal, while 30% are abnormal in some way. In 70% of the cases the sSMC is de novo, in 20% it is inherited from the mother, and in 10% it is inherited from the father. An sSMC can be causative for specific syndromes such as Emanuel, Pallister-Killian, or cat eye syndromes. There may be more specific sSMC-related syndromes, which may be identified by further investigation. These 10 syndromes can be useful for genetic counseling after further study.

Mosaic small supernumerary marker chromosome 1 at amniocentesis: prenatal diagnosis, molecular genetic analysis and literature review

We present prenatal diagnosis and molecular cytogenetic analysis of mosaic small supernumerary marker chromosome 1 [sSMC(1)]. We review the literature of sSMC(1) at amniocentesis and chromosome 1p21.1-p12 duplication syndrome. We discuss the genotype-phenotype correlation of the involved genes of ALX3, RBM15, NTNG1, SLC25A24, GPSM2, TBX15 and NOTCH2 in this case.

Rhizomelic chrondrodysplasia punctata type 2 resulting from paternal isodisomy of chromosome 1

Rhizomelic chondrodysplasia punctata (RCDP) is an autosomal-recessive disorder resulting from mutations in one of three peroxisomal genes essential for ether lipid biosynthesis, PEX7 (RCDP1), GNPAT (RCDP2), and AGPS (RCDP3). Affected patients have characteristic features including shortening of the proximal long bones, epiphyseal stippling, bilateral cataracts, growth and developmental delays. Whereas the majority of patients have RCDP type 1, around 5% have RCDP type 2 or 3. We identified a patient with RCDP type 2 and an apparent homozygous deletion, c.1428delC, after full sequencing of his GNPAT genes. The father was heterozygous for this mutation, while sequencing of the maternal GNPAT genes revealed only wild-type sequence. Southern analyses performed on parental gDNA did not show evidence of a maternal gene deletion. Amplification and fragment analysis of dinucleotide repeat markers spanning chromosome 1 in the patient and both parents revealed paternal uniparental inheritance. We discuss the potential mechanisms causing uniparental disomy (UPD) in this patient and review the literature on chromosome 1 UPD. The absence of non-RCDP clinical features in this patient was consistent with previous literature supporting the absence of imprinted genes on chromosome 1. This first description of RCDP caused by UPD dramatically changes the parental recurrence risk, highlighting the value of obtaining parental genotypes when the proband has a putative homozygous mutation by sequence analysis.

Small supernumerary marker chromosomes 1 with a normal phenotype

Small supernumerary marker chromosomes (sSMCs) are a major problem in prenatal cytogenetic diagnostics. Over two-thirds of cases carrying an sSMC derived from chromosome 1 are associated with clinical abnormalities. We report 3 further cases of such sSMCs that did not show any clinical abnormalities. All 3 sSMCs studied were detected prenatally and characterized comprehensively for their genetic content by molecular cytogenetics using subcentromere-specific multicolor fluorescence in situ hybridization, and for a possibly associated uniparental disomy. After exclusion of additional euchromatin due to the presence of sSMCs and a uniparental disomy, parents opted for continuation of the pregnancies and healthy children were born in all 3 cases. It is important to quickly and clearly characterize prenatal sSMCs. Also, all available sSMC cases need to be collected on a homepage such as the Jena Institute of Human Genetics and Anthropology sSMC homepage (http://www.med.uni-jena.de/fish/sSMC/00START.htm).

Five cases of supernumerary small ring chromosomes 1: Heterogeneity and genotype–phenotype correlation

Genetic counselling of patients with small supernumerary ring chromosomes (sSRCs) can be difficult, especially in prenatal testing, due to the complexity in establishing a karyotype-phenotype correlation. In fact, it has been estimated that about 10% of extra ring(1) chromosomes are associated with an unremarkable phenotype. We report on five new cases of extra ring chromosomes(1) manifesting different clinical outcome. One case was familial, segregating from a mother with mosaic karyotype, while the others were de novo. Ring chromosomes were characterised by FISH. In three subjects the involvement of the same euchromatic 1p region was demonstrated. Present observations corroborate previous results and provide some insight into the identification of the harmless ring(1) structures.

Zellweger syndrome resulting from maternal isodisomy of chromosome 1

Zellweger syndrome (ZS) is an autosomal recessive peroxisomal disorder that results from mutations in one of the peroxisome biogenesis (PEX) genes. This is the first patient reported with uniparental disomy (UPD) resulting in ZS, in this case maternal isodisomy of chromosome 1 involving reduction to homoallelism of a frameshift mutation within PEX 10. Other reported cases of UPD1, and evidence for the imprinting of genes on chromosome 1, are reviewed. The molecular findings in this patient have important implications for molecular testing and genetic counseling in ZS.

A set of duplicons on human chromosome 9 is involved in the origin of a supernumerary marker chromosome

Human chromosome 9 is involved in a number of recurrent structural rearrangements; moreover, its pericentromeric region exhibits a remarkable evolutionary plasticity. In this study we present the molecular characterization of a constitutional rearrangement, involving the 9p21.1q13 region, which led to the formation of a supernumerary marker chromosome (SMC). We defined the sequence of the breakpoints and identified a new set of duplicons on human chromosome 9, named LCR9s (chromosome 9 low-copy repeats). Two of these duplicons were shown to be involved in a somatic exchange leading to the formation of the SMC. High-resolution FISH coupled to database search demonstrated that a total number of 35 LCR9 paralogs are present in the human genome. These newly described chromosome 9 duplicons have features that may be crucial in driving structural chromosome rearrangements in germinal and somatic cells.

A fascination with chromosome rescue in uniparental disomy: Mendelian recessive outlaws and imprinting copyrights infringements

With uniparental disomy (UPD), the presence in a diploid genome of a chromosome pair derived from one genitor carries two main types of developmental risk: the inheritance of a recessive trait or the occurrence of an imprinting disorder. When the uniparentally derived pair carries two homozygous sequences (isodisomy) with a duplicated mutant, this 'reduction to homozygosity' determines a recessive phenotype solely inherited from one heterozygote. Thus far, some 40 examples of such recessive trait transmission have been reported in the medical literature and, among the current 32 known types of UPDs, UPD of chromosomes 1, 2, and 7 have contributed to the larger contingent of these conditions. Being at variance with the traditional mode of transmission, they constitute a group of 'Mendelian outlaws'. Several imprinted chromosome domains and loci have been, for a large part, identified through different UPDs. Thus, disomies for paternal 6, maternal 7, paternal 11, paternal and maternal 14 and 15, maternal 20 (and paternal 20q) and possibly maternal 16 cause as many syndromes, as at the biological level the loss or duplication of monoparentally expressed allele sequences constitutes 'imprinting rights infringements'. The above pitfalls represent the price to pay when, instead of a Mendelian even segregation and independent assortment of the chromosomes, the fertilized product with a nondisjunctional meiotic error undergoes correction (for unknown or fortuitous reasons) through a mitotic adjustment as a means to restore euploidy, thereby resulting in UPD. Happily enough, UPDs leading to the healthy rescue from some chromosomal mishaps also exist.

Fumarase deficiency caused by homozygous P131R mutation and paternal partial isodisomy of chromosome 1

We report on the first case of fumarase deficiency (FD) caused by uniparental isodisomy. An affected patient was found to be homozygous for the P131R mutation in the FH gene. In this nonconsanguineous family, the unaffected father was found to be heterozygous for the same mutation, and the mother was found to be homozygous wild-type. Analysis of chromosome 1 markers showed that the patient inherited both paternal alleles with complete absence of the maternal homolog. The two copies of the paternal chromosome 1 are heterodisomic for most of the chromosome except the distal 1q region which is isodisomic for the mutant alleles of the FH gene. The genotypes of other chromosome markers are consistent with the patient inheriting alleles from both parents. Although FD is an autosomal recessive disorder, the effects of uniparental disomy (UPD) should be considered in genetic counseling since the recurrence risk of an affected child is significantly reduced when the disorder is due to UPD.

Three new cases with a supernumerary ring chromosome 1

We report on three cases with a cytogenetically identical ring chromosome containing euchromatin from the long arm of chromosome 1 (r[1][::p11.1-->q21.1::]). Two cases were newborn males (Cases 1 and 2) and the third one was prenatally identified as female (Case 3). Mosaicism was present in all three cases in different degrees, i.e. 48%, 25% and 14% of the cells, respectively. Clinical signs and symptoms vary between the three cases. The results of our three cases are compared with those from the literature.

Supernumerary der(1) marker chromosome derived from a ring chromosome 1 which has retained the original centromere and euchromatin from 1q21.1 --> q21.3 with substantial loss of 1q12 heterochromatin in a female with dysmorphic features and psychomotoric developmental delay

We report on a 5.5-year-old girl with dysmorphic features and psychomotoric developmental delay with a mitotically stable supernumerary marker chromosome. The origin of the marker was identified by microdissection and reverse painting of marker DNA as the pericentromeric region of chromosome 1. Fine mapping by FISH with selected YAC or BAC clones identified no p-arm material on the marker. The marker has retained its original centromere and euchromatin from 1q21.1-q21.3 but only small remnants of the 1q12 heterochromatin. Furthermore, some FISH clones presented single signals on the marker and others presented double signals indicating a partial duplication within the marker. These observations suggest a multi-step origin of the marker most probably with ring formation as the first step.

Prenatal diagnosis of minute supernumerary marker chromosomes

The identification of supernumerary marker chromosomes (SMC) at prenatal diagnosis is problematic, particularly for the prediction of phenotype. The assessment of phenotypic risk is based on the size, morphology and origin of the SMC. Fluorescence in situ hybridization (FISH) characterization and family studies are also employed to aid in determining the significance of a prenatally ascertained SMC. Generally, SMC containing euchromatin are more likely to be associated with abnormal phenotypes and SMC without euchromatin are more likely to result in normal phenotypes. The smallest of SMC, minute SMC (minSMC) appear as dot-like or centric fragments and are particularly difficult to identify and characterize. Previous empirical observations suggested that the risk of phenotypic abnormality in prenatally ascertained minSMC was < or = 5%. We identified minSMC in chorionic villus samples (CVS) or amniocytes from 11 unrelated pregnancies. The chromosomal origin of each minSMC was identified by sequential FISH analysis with chromosome-specific centromere probes. Further FISH analysis with whole chromosome paint probes was undertaken to assess each minSMC for the presence or absence of euchromatin, since the presence of euchromatin may be associated with a higher risk of abnormality. Two minSMC were shown to have euchromatin. The first, a minSMC(12) was found in CVS but not confirmed in amniocytes, indicating confined placental mosaicism. The second, a minSMC derived from chromosome 19, was associated with ultrasound abnormalities. Apart from a case with mild speech delay, the remaining minSMC cases without detectable euchromatin had a normal outcome at birth and/or on longer term follow-up. Additional FISH analyses with a telomeric repeat probe showed no signal on any of the minSMC tested, suggesting that they were ring chromosomes in structure. These data further support the concept that minSMC containing euchromatin are more likely to be associated with an abnormal phenotype, although as more data are collected, this may vary by chromosome of origin. The absence of detectable euchromatin, while not guaranteeing a normal result, is most likely to have a normal outcome. The present report and previous studies do not yet allow any significant adjustment of the empirical < or = 5% risk estimate for minSMC identified at prenatal diagnosis. However, reporting of additional cases with characterization of the minSMC and particularly with long-term follow-up will, in time, allow for more accurate risk estimates and provide prognostic information.

Uniparental disomy (UPD) other than 15: Phenotypes and bibliography updated

Uniparental disomy (UPD) describes the inheritance of a pair of chromosomes from only one parent. The concept was introduced in Medical Genetics by Engel (1980); Am J Med Genet 6:137-143. Aside UPD 15, which is the most frequent one, up to now (February 2005) 197 cases with whole chromosome maternal UPD other than 15 (124 X heterodisomy, 59 X isodisomy, and 14 cases without information of the mode of UPD) and 68 cases with whole chromosome paternal UPD other than 15 (13 X heterdisomy, 53 X isodisomy, and 2 cases without information of the mode of UPD) have been reported. In this review we discuss briefly the problems associated with UPD and provide a comprehensive clinical summary with a bibliography for each UPD other than 15 as a guide for genetic counseling.

A chromosome 21-derived minute marker in a mosaic trisomy 21 background: implications for risk assessments in marker chromosome cases

We report a prenatal case of a chromosome 21-derived minute supernumerary marker, found as a mosaic along with a trisomy 21 cell line at amniocentesis. Follow-up analysis of other fetal tissues confirmed the mosaicism and also disclosed a normal cell line. It is likely that the marker reflects a mutation event that resulted in trisomy rescue early in embryonic development. Had the trisomy 21 cell line not been found at amniocentesis, a low risk of an abnormal phenotype (approximately 5%) would have been assigned. We suggest that the risk associated with minute non-euchromatic marker chromosomes should be revised to account for the possibility of mosaicism with potentially aneuploid populations and/or uniparental disomy (UPD). The finding of any marker chromosome should prompt a thorough investigation for aneuploid cell lines. In the case of small markers with no euchromatin, the given risk of adverse phenotypic effects is not likely to be associated with the marker per se but with the possible presence of a cryptic aneuploid cell line from which the marker may have arisen.

Characterization of a supernumerary ring chromosome 1 mosaicism in two cell systems by molecular cytogenetic techniques and review of the literature

We report on a 4-year-old boy with developmental delay and microcephaly with an additional small marker chromosome derived from chromosome 1 and detected in 14% of T-lymphocytes by conventional cytogenetics and in 9% of buccal smear cells by interphase FISH. Using molecular cytogenetic techniques, the marker chromosome was characterized as an extra ring chromosome consisting of euchromatic material from the proximal short arm of chromosome 1. We compare the cytogenetic data and the phenotype of our patient to those previously described cases with marker chromosome 1 mosaicism. We conclude that in addition to the straightforward molecular cytogenetic characterization of the euchromatic content of the ring chromosome, the investigation of a second cell system gives additional information about the tissue specific distribution of the supernumerary marker chromosome (SMC) and provides more reliable data for further karyotype/phenotype correlations and the prediction of the phenotypic outcome in prenatal cases.

Maternal uniparental isodisomy 10 and mosaicism for an additional marker chromosome derived from the paternal chromosome 10 in a fetus

We report a case of maternal isodisomy 10 combined with mosaic partial trisomy 10 (p12.31-q11.1). Chromosome examinations from a CVS sample showed a karyotype 47,XX,+mar/46,XX [corrected]. The additional marker chromosome which was present in 6/25 interphase nuclei was shown by fluorescence in situ hybridization (FISH) to have been derived from a pericentromeric segment of chromosome 10. DNA analysis was performed from umbilical cord blood from the fetus after termination of the pregnancy at 18 weeks. The results showed that the two structurally normal chromosomes 10 were both of maternal origin, whereas the marker chromosome derived from the father. Autopsy of the fetus revealed hypoplasia of heart, liver, kidneys and suprarenal glands, but, apart from a right bifid ureter, no structural organ abnormalities. This fetus represents the second reported instance of a maternal uniparental disomy (UPD) 10.