Prenatal diagnosis and molecular cytogenetic characterization of mosaicism for a small supernumerary marker chromosome derived from 2q11.1-q12.1 associated with fetal bilateral radial dysplasia.

OBJECTIVE: We present prenatal diagnosis and molecular cytogenetic characterization of mosaicism for a small supernumerary marker chromosome (sSMC) derived from 2q11.1-q12.1 associated with fetal bilateral radial dysplasia. CASE REPORT: A 27-year-old woman underwent amniocentesis at 18 weeks of gestation because of club hands on fetal ultrasound. The internal organs of the fetus were normal. Amniocentesis revealed a karyotype of 47,XY,+mar [13]/46,XY [11]. The parental karyotypes were normal. Simultaneous array comparative genomic hybridization (aCGH) analysis of the DNA extracted from uncultured amniocytes revealed the result of arr 2q11.1q12.1 (95,529,039-102,825,556) × 3.0 [GRCh37 (hg19)]. The pregnancy was terminated at 20 weeks of gestation, and a malformed fetus was delivered with isolated bilateral radial dysplasia. The cord blood had a karyotype of 47,XY,+mar[24]/46,XY[16]. Polymorphic DNA marker analysis of the DNAs extracted from umbilical cord and parental bloods excluded uniparental disomy for chromosome 2. Metaphase fluorescence in situ hybridization analysis confirmed an sSMC derived from chromosome 2q11.1-q12.1 in cultured amniocytes. CONCLUSION: High-level mosaicism for an sSMC derived from chromosome 2q11.1-q12.1 can be associated with fetal abnormalities.

Upper limb phocomelia: A prenatal case of thrombocytopenia-absent radius (TAR) syndrome illustrating the importance of chromosomal microarray in limb reduction defects.

OBJECTIVE: To describe the ultrasonographic, pathologic and molecular findings in a fetus with TAR syndrome, and to illustrate the contribution of chromosomal microarray analysis (CMA) to the etiological investigation of fetal upper limb reduction defects. CASE REPORT: A 35-year-old woman was referred for Genetic Counseling after pregnancy termination for severe upper limb bilateral phocomelia detected in the second trimester. Fetal autopsy showed severe shortening of the arms and forearms. The fetal skeletal survey confirmed the absence of the radii, ulnae and humeri. CMA revealed an interstitial deletion in 1q21 including the RBM8A gene. Subsequent Sanger sequencing of this gene identified a hypomorphic mutant allele, c.-21G > A, confirming the diagnosis of TAR syndrome. CONCLUSION: The differential diagnosis of upper limb defects is broad. Identification of their cause is essential for adequate genetic counseling including prognosis and recurrence risk estimation. CMA should be considered in fetuses with upper limb reduction defects, especially when the thumbs are present.

Unexplained right atrial enlargement may be a sign of Holt-Oram syndrome in the fetus.

Two cases of ultrasound diagnosis of Holt-Oram syndrome are described. Both were characterized by significant right atrial enlargement that was not due to concurrent tricuspid regurgitation or other cardiac anomalies. In both cases the associated skeletal anomaly was subtle and barely visible using ultrasound. Interestingly, despite the fact that Holt-Oram syndrome is also called atriodigital dysplasia, unexplained right atrial enlargement has not been described in this context in the fetus before. When such a finding is detected, we believe a thorough search for upper limb abnormalities should be carried out and genetic testing for Holt-Oram syndrome should be discussed with the parents.

Update on embryology of the upper limb.

Current concepts in the steps of upper limb development and the way the limb is patterned along its 3 spatial axes are reviewed. Finally, the embryogenesis of various congenital hand anomalies is delineated with an emphasis on the pathogenetic basis for each anomaly.

Preaxial polydactyly of the upper limb viewed as a spectrum of severity of embryonic events.

Preaxial polydactyly (PPD) is a common congenital abnormality and its classification varies among geneticists and hand surgeons. For example, the triphalangeal thumb, preaxial polysyndactyly, and the mirror hand deformity are considered as forms of PPD only in the genetics literature. Preaxial polydactyly is an error in the anteroposterior axis of the development of the upper limb. In this paper, the development of this axis is detailed and all molecular events that are known to lead to PPD are reviewed. Finally, based on the review, PPD is viewed as a spectrum of severity of embryonic events.

Regulatory variation in a TBX5 enhancer leads to isolated congenital heart disease.

Recent studies have identified the genetic underpinnings of a growing number of diseases through targeted exome sequencing. However, this strategy ignores the large component of the genome that does not code for proteins, but is nonetheless biologically functional. To address the possible involvement of regulatory variation in congenital heart diseases (CHDs), we searched for regulatory mutations impacting the activity of TBX5, a dosage-dependent transcription factor with well-defined roles in the heart and limb development that has been associated with the Holt-Oram syndrome (heart-hand syndrome), a condition that affects 1/100 000 newborns. Using a combination of genomics, bioinformatics and mouse genetic engineering, we scanned ∼700 kb of the TBX5 locus in search of cis-regulatory elements. We uncovered three enhancers that collectively recapitulate the endogenous expression pattern of TBX5 in the developing heart. We re-sequenced these enhancer elements in a cohort of non-syndromic patients with isolated atrial and/or ventricular septal defects, the predominant cardiac defects of the Holt-Oram syndrome, and identified a patient with a homozygous mutation in an enhancer ∼90 kb downstream of TBX5. Notably, we demonstrate that this single-base-pair mutation abrogates the ability of the enhancer to drive expression within the heart in vivo using both mouse and zebrafish transgenic models. Given the population-wide frequency of this variant, we estimate that 1/100 000 individuals would be homozygous for this variant, highlighting that a significant number of CHD associated with TBX5 dysfunction might arise from non-coding mutations in TBX5 heart enhancers, effectively decoupling the heart and hand phenotypes of the Holt-Oram syndrome.

Ulnar ray deficiency: a review of the classification systems, the clinical features in 72 cases, and related developmental biology.

Ulnar ray deficiency is rare and has a variable presentation. As a result, there are many different classification systems for this anomaly. Furthermore, the developmental biology of the anomaly is still not fully understood. The aim of this article is to review the previous classification systems, present the clinical features in 72 cases and discuss the developmental biology of ulnar ray deficiency.

Embryology of the upper limb.

An increased understanding of embryogenesis has advanced our fundamental knowledge of limb anomalies. Animal models with similar limb patterning have been used to dissect and manipulate crucial signaling centers that affect limb development and orientation. Experimental embryologists can produce limb anomalies that are similar to the human phenotype encountered in clinical practice. The evaluating physician must possess a basic comprehension of embryogenesis and limb formation to comprehend congenital limb anomalies and to communicate relevant knowledge to the family. This Current Concepts article is intended to provide an update of limb development that is germane to the clinical scenario.

Effects of limited doses of retinyl palmitate at the critical time of limb morphogenesis in mouse embryos.

With a view to examine the effects of defined doses of retinyl palmitate (Vit. A) on limb morphogenesis and their effects at the critical time in mouse embryos, pregnant Swiss Webster albino mice were administered retinyl palmitate (10000 or 15000 IU/kg, i.p.) on different days of pregnancy. Vitamin A in 15000 IU/kg, i.p. dose was most effective as produced malformations in the forelimbs by day 10 in 28.6% mice and in the hindlimbs by day 11 in 20.6% mice. Further, two injections in a day with the lower dose (10000 IU/kg, i.p.) had more teratogenic effects than single 15000 IU/kg, i.p. injection. Two injections of either dose on day 10 resulted in higher embryo absorption.

Pediatric upper extremity conditions: traumatic and congenital.

There are a variety of upper extremity conditions both traumatic and congenital that the physician will encounter. Some require emergent treatment; some should be observed. It is important to make the correct diagnosis and refer in a timely fashion.

Cadmium-induced postaxial forelimb ectrodactyly: association with altered sonic hedgehog signaling.

Administration of CdSO(4) to C57BL/6 mice at day 9.5 of gestation induces a high incidence of postaxial forelimb ectrodactyly in the offspring. We propose that Cd(2+) exposure impairs the process of anterior/posterior formation in the limb bud, a process that is directed by Sonic hedgehog (Shh) signaling. We show that exposure of the mouse embryo to Cd(2+) disrupts Shh signaling as measured by polarizing activity of mouse limb bud ZPA grafted to a host chick wing, and activity of a Gli:luciferase reporter exposed to limb bud lysates. Yet the expression of Shh and its translation are not affected by Cd(2+) exposure. We propose that teratogen exposure affects the processing of Shh in the cells in which it is made.

Time, pattern, and heterochrony: a study of hyperphalangy in the dolphin embryo flipper.

The forelimb of whales and dolphins is a flipper that shows hyperphalangy (numerous finger bones). Hyperphalangy is also present in marine reptiles, including ichthyosaurs and plesiosaurs. The developmental basis of hyper-phalangy is unclear. Kükenthal suggested that phalanx anlagen split into three pieces during cetacean development, thereby multiplying the ancestral number. Alternatively, Holder suggested that apical ectodermal ridge (AER)-directed limb outgrowth might be prolonged by a timing shift (heterochrony), leading to terminal addition of extra phalanges. We prepared a series of whole mounted and serially sectioned embryonic flipper buds of the spotted dolphin Stenella attenuata. This cetacean shows marked hyperphalangy on digits II and III. We confirm previous reports that the proximodistal laying down of phalanges is prolonged in digits II and III. Histology showed that the apical ectoderm was thickened into a cap. There was a weak ridge-like structure in some embryos. The cap or ridge formed part of a bud-like mass that persisted on digits II and III at stages when it had disappeared from other digits. Thus the dolphin differs from other mammals in showing a second period of limb outgrowth during which localized hyperphalangy develops. New phalanges only formed at the tip of the digits. These findings are consistent with a model in which heterochrony leads to the terminal addition of new phalanges. Our results are more easily reconciled with the progress zone model than one in which the AER is involved in the expansion of a prepattern. We suggest that patterning mechanisms with a temporal component (i.e., the "progress zone" mechanism) are potential targets for heterochrony during limb evolution.