Prenatal diagnosis of complete paternal uniparental isodisomy for chromosome 3: a case report

Background Uniparental disomy (UPD) is defined as an inheritance of two chromosomes from only one of the parents with no representative copy from the other. Paternal-origin UPD of chromosome 3 is a very rare condition, with only five cases of paternal UPD(3) reported. Case presentation Here, we report a prenatal case that is only the second confirmed paternal UPD(3) reported with no apparent disease phenotype. The fetus had a normal karyotype and normal ultrasound features throughout gestation. Copy neutral regions of homozygosity on chromosome 3 were identified by single nucleotide polymorphism (SNP) array. Subsequent SNP array data of parent–child trios showed that the fetus carried complete paternal uniparental isodisomy (isoUPD) of chromosome 3. The parents decided to continue with the pregnancy after genetic counseling, and the neonate had normal physical findings at birth and showed normal development after 1.5 years. Conclusions These findings provided further evidence to confirm that there were no important imprinted genes on paternal chromosome 3 that caused serious diseases and a reference for the prenatal diagnosis and genetic counseling of UPD(3) in the future.

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, while 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 upregulated beyond double-dose expectation (6-fold). 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 upregulated. This case broadens the phenotypic spectrum of UPDs but did not show evidence of involvement of an imprinted gene network.

Prenatal Diagnosis of Complete Paternal Uniparental Isodisomy for Chromosome 3: A Case Report

Background Paternal uniparental disomy (UPD) of chromosome 3 is a very rare condition. At present, only 5 cases of paternal UPD(3) has been reported. This was the second ascertained paternal UPD(3) with no apparent disease phenotype.Case presentation We hereby reported a case of a fetus with normal karyotype and normal ultrasound features at the whole gestation. A copy neutral regions of homozygosity on chromosome 3 was indentified by Single Nucleotide Polymophism array (SNP array). Subsequent SNP array data of parent–child trios showed the fetus has carried complete paternal uniparental isodisomy (isoUPD) of chromosome 3. The parents decided to continue the pregnancy after genetic counseling. The neonate had normal physical findings at birth and develops normally after 1.5 years. Conclusions The findings could provide further evidence to confirm that there was no important imprinted genes causing serious diseases on paternal chromosome 3 and provided a reference for the prenatal diagnosis and genetic counseling of UPD(3) in the future.

A Case of Sporadic Pseudohypoparathyroidism Type 1B Presented with Hypokalemia

Dear EditorLuo et al. 1 reported two cases of autosomal dominant pseudohypoparathyroidism type 1B (AD-PHP1B) and reviewed literature about the genetic and epigenetic characteristics of AD-PHP1B. Pseudohypoparathyroidism (PHP) is a cluster of heterogeneous diseases characterized by hypocalcemia and hyperphosphatemia due to resistance to parathyroid hormone (PTH). PHP1B almost results from methylation abnormalities of the maternal differentially methylated regions (DMRs) and can be divided into sporadic PHP1B and AD-PHP1B 1. As mentioned in this article 1, AD-PHP1B is caused by heterozygous maternal deletions within GNAS or STX16, which are associated with loss of methylation at the A/B DMR alone or at all maternally methylated GNAS exons. While sporadic PHP1B remains unclear at the molecular level, except for approximately 10% of the patients caused by paternal uniparental isodisomy or heterodisomy involving chromosome 20q (patUPD20q) 2. Here, we would like to present a rare case of sporadic PHP1B occurring in association with hypokalemia.

Paternal Uniparental Isodisomy of Chromosome 2 in a Patient with CNGA3-Associated Autosomal Recessive Achromatopsia

Achromatopsia (ACHM) is a rare autosomal recessively inherited retinal disease characterized by congenital photophobia, nystagmus, low visual acuity, and absence of color vision. ACHM is genetically heterogeneous and can be caused by biallelic mutations in the genes CNGA3, CNGB3, GNAT2, PDE6C, PDE6H, or ATF6. We undertook molecular genetic analysis in a single female patient with a clinical diagnosis of ACHM and identified the homozygous variant c.778G>C;p.(D260H) in the CNGA3 gene. While segregation analysis in the father, as expected, identified the CNGA3 variant in a heterozygous state, it could not be displayed in the mother. Microsatellite marker analysis provided evidence that the homozygosity of the CNGA3 variant is due to partial or complete paternal uniparental isodisomy (UPD) of chromosome 2 in the patient. Apart from the ACHM phenotype, the patient was clinically unsuspicious and healthy. This is one of few examples proving UPD as the underlying mechanism for the clinical manifestation of a recessive mutation in a patient with inherited retinal disease. It also highlights the importance of segregation analysis in both parents of a given patient or especially in cases of homozygous recessive mutations, as UPD has significant implications for genetic counseling with a very low recurrence risk assessment in such families.