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Correspondence to Dr Akie Nakamura, Department of Molecular Endocrinology, National Research Institute for Child Health and Development, Tokyo 157-8535, Japan; [email protected] and Masayo Kagami, Department of Molecular Endocrinology, National Research Institute for Child Health and Development, Tokyo, Japan; [email protected]
Introduction
The condition in which both homologous chromosomes are derived from only one parent is referred to as uniparental disomy (UPD). When UPD takes place on chromosomes involving imprinted genes, the expression of which is determined by the parent of origin, the disruption of these gene expression results in imprinting disorders.1 It is well known that several imprinted genes play an essential role in human growth and development. In general, paternally expressed imprinted genes enhance growth, while maternally expressed imprinted genes suppress growth.2 Consequently, imprinting disorders lead to growth-related disorders. Furthermore, UPD has the potential to cause autosomal-recessive diseases because of the loss of heterozygosity in the mutated allele.
The human chromosome 7 carries several imprinted genes, and it is well known that maternal UPD for chromosome 7 (upd(7)mat) results in Silver-Russell syndrome (SRS) (OMIM #180860), characterised by prenatal and postnatal growth retardation, relative macrocephaly and a specific facial appearance.3 In contrast, the clinical manifestation of upd(7)pat remains largely unclear, because only four cases have been previously reported.4–7 As they were accompanied by autosomal-recessive disorders which have the possibility to result in growth retardation,4–7 the relevance of upd(7)pat to the overgrowth phenotype remains unknown. Here we describe one case of paternal isodisomy with no additional genetic disease that may answer the question.
Subjects and methods
Case report
The patient, a Japanese boy, was born after artificial intrauterine insemination with concomitant human menopausal gonadotropin and delivered at 34-week gestation via vaginal delivery as a dichorionic diamniotic twin brother. His birth weight, length and occipitofrontal circumference (OFC) was 2445 g (+0.85 standard deviation (SD)), 46.5 cm (+0.97 SD) and 33.0 cm (+1.28 SD), respectively. SD scores of birth length, weight and OFC were evaluated on the basis of the gestational age-matched and sex-matched Japanese reference data (http://jspe.umin.jp/medical/keisan.html). His twin sister’s birth weight, length and OFC were 1730 g (−1.35 SD), 42.5 cm (−0.79 SD) and 31.2 cm (+0.13 SD), respectively. The fused placenta weighed 1380 g, which was large relative to their birth...