Maternal isochromosome 7q and paternal isochromosome 7p in a boy with growth retardation

Case report: Paternal uniparental disomy on chromosome 7 and homozygous SUGCT mutation in a fetus with overweight after birth

Background: Paternal uniparental disomy (UPD) of chromosome 7 is extremely rare, and only a few postnatal cases have been reported. The effects on growth were discordant in these cases, and the relevance of paternal UPD(7) to growth caused by imprinting remains questionable. Case presentation: Here, we report a prenatal case that underwent invasive prenatal diagnosis due to the high risk of Down's syndrome and failed noninvasive prenatal screening. The fetus had a normal karyotype and no apparent copy number variation. Homozygous copy-neutral regions on chromosome 7 were identified using a single nucleotide polymorphism (SNP) array; the data for the parent-child trios showed that the fetus carried the whole paternal isodisomy of chromosome 7. Whole exome and Sanger sequencing revealed a homozygous frameshift mutation in SUGCT at 7p14.1, from the heterozygous carrier father, with no contribution from the mother. The parents decided to continue with the pregnancy after genetic counseling, and the neonate had normal physical findings at birth and showed overweight after birth during a long-term intensive follow-up. Conclusion: We report the first prenatal case who carried paternal UPD(7) and homozygous SUGCT mutation with an overweight phenotype after birth. The overweight may be caused by paternal UPD(7) or homozygous frameshift mutation of SUGCT, or both of them, but it is unclear which contributes more.

Double paternal uniparental isodisomy 7 and 15 presenting with Beckwith-Wiedemann spectrum features

Here we describe for the first time double paternal uniparental isodisomy (iUPD) 7 and 15 in a baby boy with features in the Beckwith–Wiedemann syndrome spectrum (BWSp) (placentomegaly, hyperinsulinism, enlarged viscera, hemangiomas, and earlobe creases) in addition to conjugated hyperbilirubinemia. His phenotype was also reminiscent of genome-wide paternal uniparental isodisomy. We discuss the most likely origin of the UPDs: a maternal double monosomy 7 and 15 rescued by duplication of the paternal chromosomes after fertilization. So far, paternal UPD7 is not associated with an abnormal phenotype, whereas paternal UPD15 causes Angelman syndrome. Methylation analysis for other clinically relevant imprinting disorders, including BWSp, was normal. Therefore, we hypothesized that the double UPD affected other imprinted genes. To look for such effects, patient fibroblast RNA was isolated and analyzed for differential expression compared to six controls. We did not find apparent transcription differences in imprinted genes outside Chromosomes 7 and 15 in patient fibroblast. PEG10 (7q21.3) was the only paternally imprinted gene on these chromosomes up-regulated beyond double-dose expectation (sixfold). We speculate that a high PEG10 level could have a growth-promoting effect as his phenotype was not related to aberrations in BWS locus on 11p15.5 after DNA, RNA, and methylation testing. However, many genes in gene sets associated with growth were up-regulated. This case broadens the phenotypic spectrum of UPDs but does not show evidence of involvement of an imprinted gene network.

Microdeletions of the 7q32.2 imprinted region are associated with Silver-Russell syndrome features

The association of maternal uniparental disomy of human chromosome 7 (upd(7) mat) and the growth retardation disorder Silver-Russell syndrome (SRS) is well established, but the causative gene or region is currently unknown. However, several observations indicate that molecular alterations of the genomically imprinted MEST region in 7q32.2 are associated with growth retardation and a phenotype reminiscent to SRS. We now report on a second patient with a similar phenotype and a de novo 7q32.2 microdeletion including MEST affecting the paternal allele. This confirms the central role of imprinted genes in 7q32.2 in the etiology of a growth retardation phenotype associated with SRS features.

Initial maternal meiotic I error leading to the formation of a maternal i(2q) and a paternal i(2p) in a healthy male

We report on the investigation of the parental origin and mode of formation of the two isochromosomes, i(2p) and i(2q), detected in a healthy adult male. Conventional cytogenetic analysis revealed the proband's lack of structurally normal chromosomes 2, these being replaced by an i(2p) and an i(2q). Investigation of the parental origin of the isochromosomes revealed a paternal origin of the i(2p) chromosome and a maternal origin of the i(2q) chromosome. Thus, the formation of both isochromosomes, or at least of the paternal i(2p), appears to have occurred postzygotically. Interestingly, whilst a paternal isodisomy was observed for the entire 2p, maternal heterodisomy was detected for two segments of 2q, separated by a segment showing isodisomy. The results are indicative of an initial error (non-disjunction or i(2q) formation) concerning the maternal chromosomes 2 during meiosis I, which likely favored the subsequent mitotic recombination event resulting in the presence of two isochromosomes. To the best of our knowledge this is the first case of an initial meiotic error, followed by postzygotic trisomy rescue through the formation of isochromosomes, resulting in a normal phenotype. A prenatal detection, by cytogenetic and molecular analysis, of such chromosome abnormality would have led to the incorrect conclusion of a most likely poor prognosis for the fetus.

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.