Sirenomelia: An anatomical assessment and genetic sex determination of two cases.

The etiology of sirenomelia is currently unknown. Data are limited in comparing external and internal abnormalities using modern imaging technologies and molecular genetic analysis. The purpose of the current study was designed to compare external and internal anatomical defects in two cases of sirenomelia and Potter's sequence. Considered rare, Potter's sequence is a fetal disorder with characteristic features of bilateral renal agenesis, obstructive uropathy, atypical facial appearance, and limb malformations. The internal and external malformations of two term fetuses with sirenomelia and Potter's sequence were compared using assessment of external features, radiography and MRI on internal structures, and molecular genetic studies on sex determination. Data reveal that both fetuses were male and manifested with an overlapping but distinct spectrum of abnormalities. Principal differences were noted in the development of the ears, brain, urogenital system, lower limbs, pelvis, and vertebral column. Defects of the axial mesoderm are likely to underlie the abnormalities seen in both fetuses. The first one, which had only caudal defects, was found to have a spectrum of abnormalities most similar to those associated with more severe forms of the small pelvic outlet syndrome, although the structure and orientation of the sacrum and iliae were different from previously reported cases. The other had both caudal and cranial defects, and was most similar to those described in the axial mesodermal dysplasia syndrome. Defects associated with sirenomelia can be evaluated with standard gross anatomy examination, radiology, MRI, and modified PCR techniques to determine anatomical abnormalities and the sex of preserved specimens, respectively. Evidence indicated that sirenomelia could be developed via various etiologies.

Homozygous Null TBX4 Mutations Lead to Posterior Amelia with Pelvic and Pulmonary Hypoplasia.

The development of hindlimbs in tetrapod species relies specifically on the transcription factor TBX4. In humans, heterozygous loss-of-function TBX4 mutations cause dominant small patella syndrome (SPS) due to haploinsufficiency. Here, we characterize a striking clinical entity in four fetuses with complete posterior amelia with pelvis and pulmonary hypoplasia (PAPPA). Through exome sequencing, we find that PAPPA syndrome is caused by homozygous TBX4 inactivating mutations during embryogenesis in humans. In two consanguineous couples, we uncover distinct germline TBX4 coding mutations, p.Tyr113∗ and p.Tyr127Asn, that segregated with SPS in heterozygous parents and with posterior amelia with pelvis and pulmonary hypoplasia syndrome (PAPPAS) in one available homozygous fetus. A complete absence of TBX4 transcripts in this proband with biallelic p.Tyr113∗ stop-gain mutations revealed nonsense-mediated decay of the endogenous mRNA. CRISPR/Cas9-mediated TBX4 deletion in Xenopus embryos confirmed its restricted role during leg development. We conclude that SPS and PAPPAS are allelic diseases of TBX4 deficiency and that TBX4 is an essential transcription factor for organogenesis of the lungs, pelvis, and hindlimbs in humans.

Roberts syndrome in an Indian patient with humeroradial synostosis, congenital elbow contractures and a novel homozygous splice variant in ESCO2.

Roberts syndrome (also known as Roberts-SC phocomelia syndrome) is an autosomal recessive developmental disorder, characterized by pre- and postnatal growth retardation, limb malformations including bilateral symmetric tetraphocomelia or mesomelia, and craniofacial dysmorphism. Biallelic loss-of-function variants in ESCO2, which codes for establishment of sister chromatid cohesion N-acetyltransferase 2, cause Roberts syndrome. Phenotypic spectrum among patients is broad, challenging clinical diagnosis in mildly affected individuals. Here we report a 3-year-old boy with a mild phenotype of Roberts syndrome with bilateral elbow contractures, humeroradial synostosis, mild lower limb disparity, and facial dysmorphism. Trio whole-exome sequencing identified the novel biallelic splice variant c.1673+1G>A in ESCO2 in the patient. Aberrant ESCO2 pre-mRNA splicing, reduced relative ESCO2 mRNA amount, and characteristic cytogenetic defects, such as premature centromere separation, heterochromatin repulsion, and chromosome breaks, in patient cells strongly supported pathogenicity of the ESCO2 variant affecting one of the highly conserved guanine-thymine dinucleotide of the donor splice site. Our case highlights the difficulty in establishing a clinical diagnosis in individuals with minor clinical features of Roberts syndrome and normal intellectual and social development. However, next-generation sequencing tools allow for molecular diagnosis in cases presenting with mild developmental defects.

Sirenomelia and maternal chlamydia trachomatis infection: a case report and review.

Background: Sirenomelia is a lethal congenital anomaly, presenting with fusion of lower extremities and malformed perineum. The pathogenesis is unclear, and "defective blastogenesis" is the proposed mechanism. Chlamydia trachomatis (CT) is an obligate intracellular pathogen which reportedly invades placenta and may result in fetal demise. It has documented cytopathogenic effects, specifically, cellular disruption, tissue dysgenesis, and genomic instability.Case report: An infant with sirenomelia was born as a product of 30 weeks of pregnancy, which was normal except for a persistent maternal CT infection. The infant expired shortly after birth.Conclusion: Fetal invasion by CT, conceivably, may induce structural anomalies, such as sirenomelia by virtue of its cytopathic effects. We intend to draw attention to such a possibility by reporting this case. This association, however, is speculative and more cases of sirenomelia with CT positive mothers need to be described in order to make definite conclusions about such a relationship.

Repeated removal of developing limb buds permanently reduces appendage size in the highly-regenerative axolotl.

Matching appendage size to body size is fundamental to animal function. Generating an appropriately-sized appendage is a robust process executed during development which is also critical for regeneration. When challenged, larger animals are programmed to regenerate larger limbs than smaller animals within a single species. Understanding this process has important implications for regenerative medicine. To approach this complex question, models with altered appendage size:body size ratios are required. We hypothesized that repeatedly challenging axolotls to regrow limb buds would affect their developmental program resulting in altered target morphology. We discovered that after 10 months following this experimental procedure, limbs that developed were permanently miniaturized. This altered target morphology was preserved upon amputation and regeneration. Future experiments using this platform should provide critical information about how target limb size is encoded within limb progenitors.

Cohesinopathies of a feather flock together.

Roberts Syndrome (RBS) and Cornelia de Lange Syndrome (CdLS) are severe developmental maladies that present with nearly an identical suite of multi-spectrum birth defects. Not surprisingly, RBS and CdLS arise from mutations within a single pathway--here involving cohesion. Sister chromatid tethering reactions that comprise cohesion are required for high fidelity chromosome segregation, but cohesin tethers also regulate gene transcription, promote DNA repair, and impact DNA replication. Currently, RBS is thought to arise from elevated levels of apoptosis, mitotic failure, and limited progenitor cell proliferation, while CdLS is thought to arise, instead, from transcription dysregulation. Here, we review new information that implicates RBS gene mutations in altered transcription profiles. We propose that cohesin-dependent transcription dysregulation may extend to other developmental maladies; the diagnoses of which are complicated through multi-functional proteins that manifest a sliding scale of diverse and severe phenotypes. We further review evidence that cohesinopathies are more common than currently posited.

Neurocognitive profile of a young adolescent with DK phocomelia/von Voss phocomelia/von Voss Cherstvoy syndrome.

DK phocomelia/von Voss Cherstvoy syndrome is a rare condition characterized by upper limb and urogenital abnormalities and various brain anomalies. Previously reported cases have noted significant developmental delays, although no formal testing of cognitive abilities has been reported. In this paper we describe results from a comprehensive neuropsychological evaluation of a 12-year-old male with DK phocomelia syndrome. Test findings indicated mild impairment in intellectual functioning, with more significant impairment in adaptive skills and academic achievement. The neuropsychological profile converged with neurological findings, showing a distinct pattern of strengths and weaknesses that suggests functional compromise of posterior brain regions with relatively well-preserved functioning of more anterior regions. Specifically, impairments were evident in perceptual reasoning, visual perception, and visuomotor integration, whereas normal or near normal functioning was evident in memory, receptive language, social cognition, attention, and most aspects of executive functioning. To our knowledge this is the first report to describe the neurocognitive profile of an individual with DK phocomelia syndrome.

A reevaluation of X-irradiation-induced phocomelia and proximodistal limb patterning.

Phocomelia is a devastating, rare congenital limb malformation in which the long bones are shorter than normal, with the upper portion of the limb being most severely affected. In extreme cases, the hands or fingers are attached directly to the shoulder and the most proximal elements (those closest to the shoulder) are entirely missing. This disorder, previously known in both autosomal recessive and sporadic forms, showed a marked increase in incidence in the early 1960s due to the tragic toxicological effects of the drug thalidomide, which had been prescribed as a mild sedative. This human birth defect is mimicked in developing chick limb buds exposed to X-irradiation. Both X-irradiation and thalidomide-induced phocomelia have been interpreted as patterning defects in the context of the progress zone model, which states that a cell's proximodistal identity is determined by the length of time spent in a distal limb region termed the 'progress zone'. Indeed, studies of X-irradiation-induced phocomelia have served as one of the two major experimental lines of evidence supporting the validity of the progress zone model. Here, using a combination of molecular analysis and lineage tracing in chick, we show that X-irradiation-induced phocomelia is fundamentally not a patterning defect, but rather results from a time-dependent loss of skeletal progenitors. Because skeletal condensation proceeds from the shoulder to fingers (in a proximal to distal direction), the proximal elements are differentially affected in limb buds exposed to radiation at early stages. This conclusion changes the framework for considering the effect of thalidomide and other forms of phocomelia, suggesting the possibility that the aetiology lies not in a defect in the patterning process, but rather in progenitor cell survival and differentiation. Moreover, molecular evidence that proximodistal patterning is unaffected after X-irradiation does not support the predictions of the progress zone model.

[A neonate with aprosopia, monomelia and celosomy]. / Un cas de nouveau-né affecté d'une aprosopie, d'une monomélie et d'une célosomie.

The specimen of which it is a matter here takes part of the heritage of the Museum of Anatomy and Embryology of the Faculty of Medicine of the Université Libre de Bruxelles. Its medical history is completely unknown, because it takes part of an ancient collection of pathological anatomy saved from destruction and recovered by the laboratory of Anatomy and Embryology. The specimen is strongly folded up on itself ("in extension"), its length so arranged is about 25 cm; unfolded, it develops to 45 cm. Cranial perimeter is of 31 cm. Unfortunately, the brain was removed during the initial analysis, and only the examination of the braincase allows to draw some conclusions on the probable state of the encephalon. The face is rudimentary, without any orbit, and the oral cavity is limited to a vertical slit, revealing small strongly tipped up maxillary bones. A double proboscis is present. The trunk is characterised by a rather broad celosomy, with exhibition of the intestines, the liver and the pancreas. Anal atresia is observed, and the external sexual organs are hypoplastic and ambiguous. The whole left lower limb is absent, including the left half of the pelvis, corresponding to a left unilateral complete ectromelia. The neck is in hyperextension, so that the occipital region seems extremely welded in the cervical spine. However, CT examination does not confirm the presence of such fusion, but on the other hand, reveals a severe axial diversion of the spine with hyperextension. Extremely rare in humans, the aprosopia is more readily present in some animals (sheep). Its association with a monomelia and a celosomy seems not yet described.

Microduplications encompassing the Sonic hedgehog limb enhancer ZRS are associated with Haas-type polysyndactyly and Laurin-Sandrow syndrome.

Laurin-Sandrow syndrome (LSS) is a rare autosomal dominant disorder characterized by polysyndactyly of hands and/or feet, mirror image duplication of the feet, nasal defects, and loss of identity between fibula and tibia. The genetic basis of LSS is currently unknown. LSS shows phenotypic overlap with Haas-type polysyndactyly (HTS) regarding the digital phenotype. Here we report on five unrelated families with overlapping microduplications encompassing the Sonic hedgehog (SHH) limb enhancer ZPA regulatory sequence (ZRS) on chromosome 7q36. Clinically, the patients show polysyndactyly phenotypes and various types of lower limb malformations ranging from syndactyly to mirror image polydactyly with duplications of the fibulae. We show that larger duplications of the ZRS region (>80 kb) are associated with HTS, whereas smaller duplications (<80 kb) result in the LSS phenotype. On the basis of our data, the latter can be clearly distinguished from HTS by the presence of mirror image polysyndactyly of the feet with duplication of the fibula. Our results expand the clinical phenotype of the ZRS-associated syndromes and suggest that smaller duplications (<80 kb) are associated with a more severe phenotype. In addition, we show that these small microduplications within the ZRS region are the underlying genetic cause of Laurin-Sandrow syndrome.

Amelia-meromelia sequence with atrial septal defect-a rare occurrence.

Amelia and Meromelia may either present as an isolated defect or associated with other malformations; and the diagnosis is mainly clinical. The antenatal period of the case presented here was medically unsupervised but uneventful. The baby had bilateral upper limb Meromelia and bilateral lower limb Amelia along with a small ostium secundum atrial septal defect. Except for the young age of mother, there was no other obvious risk factor in this case. The baby had a normal and healthy neonatal outcome whereas most such cases are either stillborn or end in early neonatal death.

Limb reduction in an Esco2 cohesinopathy mouse model is mediated by p53-dependent apoptosis and vascular disruption.

Roberts syndrome (RBS) is an autosomal recessive disorder with profound growth deficiency and limb reduction caused by ESCO2 loss-of-function variants. Here, we elucidate the pathogenesis of limb reduction in an Esco2fl/fl;Prrx1-CreTg/0 mouse model using bulk- and single-cell-RNA-seq and gene co-expression network analyses during embryogenesis. Our results reveal morphological and vascular defects culminating in hemorrhage of mutant limbs at E12.5. Underlying this abnormal developmental progression is a pre-apoptotic, mesenchymal cell population specific to mutant limb buds enriched for p53-related signaling beginning at E9.5. We then characterize these p53-related processes of cell cycle arrest, DNA damage, cell death, and the inflammatory leukotriene signaling pathway in vivo. In utero treatment with pifithrin-α, a p53 inhibitor, rescued the hemorrhage in mutant limbs. Lastly, significant enrichments were identified among genes associated with RBS, thalidomide embryopathy, and other genetic limb reduction disorders, suggesting a common vascular etiology among these conditions.

A fetus with hemifacial microsomia and sirenomelia. The same mesodermal defect spectrum?

Sirenomelia is the most severe malformation complex affecting the human caudal pole, although its etiology is unclear, a primary defect of blastogenesis has been proposed. Studies consider sirenomelia as the most severe form of caudal dysgenesis, VACTERL association, or axial mesodermal dysplasia, although others still support the idea of a different pathologic entity. We report the prenatal, clinical, and pathologic features of a fetus with cleft lip and palate, microtia, cardiac, renal and intestinal malformations, radial aplasia, and sirenomelia. Karyotype, chromosomal breakage studies, and SHH sequence analysis were normal. The occurrence of cephalic, midline-paramedial, and caudal malformations in the same patient imply the diagnosis of hemifacial microsomia and sirenomelia. These entities are part of the same mesodermal malformation spectrum and the clinical presentation depends on environmental and genetic interactions in embrionic development. Future clinical and genome wide studies will help to better delineate this spectrum.

[Sirenomelia--a rare cause of an oligoanhydramnion in the second trimester--a case report]. / Sirenomelie--eine seltene Ursache für ein Oligo-hydramnion im zweiten Trimester--Ein Fallbericht.

Sirenomelia is a rare, but complex and lethal malformation. It is caused by a primary defect of the caudal axial skeleton and damage to the primary streak, which appears due to a vascular steal phenomenon. Sirenomelia appears sporadic with an incidence of 1-64,000 births. A risk for sirenomelia can be also found in patients with poorly controlled diabetes mellitus and in monocygotic twins. Leading ultrasound findings are fusioned lower extremities, bilateral renal agenesis, single umbilical artery and a distinct oligohydramnios. 3D ultrasound and color Doppler sonography can additionally be used for diagnostic, as well as amnioninfusion. There are 3 forms of sirenomelia, depending on missing or presence of the feet it is distinguished as sympus apus, monopus or dipus. We are presenting a case of sirenomelia with sympus dipus, which was transferred for further diagnostic of severe oligohydramnios in 21 weeks of gestation by the gynecologist.

"Laurin-Sandrow Syndrome - a review of the literature and classification system".

INTRODUCTION: Laurin-Sandrow syndrome also known as tetramelic mirror-image polydactyly is a rare congenital disorder characterized classically by polysyndactyly of the hands, mirror feet and nose anomalies (hypoplasia of the nasal alae and short columella) often associated with ulnar and/or fibular duplication. As a pathologic entity, it is heterogeneous, the patients displaying a variety of symptoms. This review aims to analyze the different aspects of the condition, such as clinical findings and methods of treatment to summarize the principal features of Laurin-Sandrow syndrome. MATERIALS AND METHODS: The review is based on searches on PubMed, Web of Science and Researchgate of the following terms: "Laurin-Sandrow syndrome", "mirror hands", "mirror feet", "tetramelic mirror-image polydactyly", "fibular dimelia" and "ulnar dimelia". Clinical cases, reviews and original articles were included. RESULTS: As a consequence of our findings, we suggest a modification of the Al-Qattan classification system for Mirror Hand-Multiple Hand Spectrum. CONCLUSION: Even though it has an extremely low incidence, a thorough understanding of the syndrome enables the surgeon to choose the appropriate treatment with the ultimate goal to improve the patient's life quality.

Genetically induced redox stress occurs in a yeast model for Roberts syndrome.

Roberts syndrome (RBS) is a multispectrum developmental disorder characterized by severe limb, craniofacial, and organ abnormalities and often intellectual disabilities. The genetic basis of RBS is rooted in loss-of-function mutations in the essential N-acetyltransferase ESCO2 which is conserved from yeast (Eco1/Ctf7) to humans. ESCO2/Eco1 regulate many cellular processes that impact chromatin structure, chromosome transmission, gene expression, and repair of the genome. The etiology of RBS remains contentious with current models that include transcriptional dysregulation or mitotic failure. Here, we report evidence that supports an emerging model rooted in defective DNA damage responses. First, the results reveal that redox stress is elevated in both eco1 and cohesion factor Saccharomyces cerevisiae mutant cells. Second, we provide evidence that Eco1 and cohesion factors are required for the repair of oxidative DNA damage such that ECO1 and cohesin gene mutations result in reduced cell viability and hyperactivation of DNA damage checkpoints that occur in response to oxidative stress. Moreover, we show that mutation of ECO1 is solely sufficient to induce endogenous redox stress and sensitizes mutant cells to exogenous genotoxic challenges. Remarkably, antioxidant treatment desensitizes eco1 mutant cells to a range of DNA damaging agents, raising the possibility that modulating the cellular redox state may represent an important avenue of treatment for RBS and tumors that bear ESCO2 mutations.

Phocomelia: a worldwide descriptive epidemiologic study in a large series of cases from the International Clearinghouse for Birth Defects Surveillance and Research, and overview of the literature.

Epidemiologic data on phocomelia are scarce. This study presents an epidemiologic analysis of the largest series of phocomelia cases known to date. Data were provided by 19 birth defect surveillance programs, all members of the International Clearinghouse for Birth Defects Surveillance and Research. Depending on the program, data corresponded to a period from 1968 through 2006. A total of 22,740,933 live births, stillbirths and, for some programs, elective terminations of pregnancy for fetal anomaly (ETOPFA) were monitored. After a detailed review of clinical data, only true phocomelia cases were included. Descriptive data are presented and additional analyses compared isolated cases with those with multiple congenital anomalies (MCA), excluding syndromes. We also briefly compared congenital anomalies associated with nonsyndromic phocomelia with those presented with amelia, another rare severe congenital limb defect. A total of 141 phocomelia cases registered gave an overall total prevalence of 0.62 per 100,000 births (95% confidence interval: 0.52-0.73). Three programs (Australia Victoria, South America ECLAMC, Italy North East) had significantly different prevalence estimates. Most cases (53.2%) had isolated phocomelia, while 9.9% had syndromes. Most nonsyndromic cases were monomelic (55.9%), with an excess of left (64.9%) and upper limb (64.9%) involvement. Most nonsyndromic cases (66.9%) were live births; most isolated cases (57.9%) weighed more than 2,499 g; most MCA (60.7%) weighed less than 2,500 g, and were more likely stillbirths (30.8%) or ETOPFA (15.4%) than isolated cases. The most common associated defects were musculoskeletal, cardiac, and intestinal. Epidemiological differences between phocomelia and amelia highlighted possible differences in their causes.

Sirenomelia: an epidemiologic study in a large dataset from the International Clearinghouse of Birth Defects Surveillance and Research, and literature review.

Sirenomelia is a very rare limb anomaly in which the normally paired lower limbs are replaced by a single midline limb. This study describes the prevalence, associated malformations, and maternal characteristics among cases with sirenomelia. Data originated from 19 birth defect surveillance system members of the International Clearinghouse for Birth Defects Surveillance and Research, and were reported according to a single pre-established protocol. Cases were clinically evaluated locally and reviewed centrally. A total of 249 cases with sirenomelia were identified among 25,290,172 births, for a prevalence of 0.98 per 100,000, with higher prevalence in the Mexican registry. An increase of sirenomelia prevalence with maternal age less than 20 years was statistically significant. The proportion of twinning was 9%, higher than the 1% expected. Sex was ambiguous in 47% of cases, and no different from expectation in the rest. The proportion of cases born alive, premature, and weighting less than 2,500 g were 47%, 71.2%, and 88.2%, respectively. Half of the cases with sirenomelia also presented with genital, large bowel, and urinary defects. About 10-15% of the cases had lower spinal column defects, single or anomalous umbilical artery, upper limb, cardiac, and central nervous system defects. There was a greater than expected association of sirenomelia with other very rare defects such as bladder exstrophy, cyclopia/holoprosencephaly, and acardia-acephalus. The application of the new biological network analysis approach, including molecular results, to these associated very rare diseases is suggested for future studies.

Amelia: a multi-center descriptive epidemiologic study in a large dataset from the International Clearinghouse for Birth Defects Surveillance and Research, and overview of the literature.

This study describes the epidemiology of congenital amelia (absence of limb/s), using the largest series of cases known to date. Data were gathered by 20 surveillance programs on congenital anomalies, all International Clearinghouse for Birth Defects Surveillance and Research members, from all continents but Africa, from 1968 to 2006, depending on the program. Reported clinical information on cases was thoroughly reviewed to identify those strictly meeting the definition of amelia. Those with amniotic bands or limb-body wall complex were excluded. The primary epidemiological analyses focused on isolated cases and those with multiple congenital anomalies (MCA). A total of 326 amelia cases were ascertained among 23,110,591 live births, stillbirths and (for some programs) elective terminations of pregnancy for fetal anomalies. The overall total prevalence was 1.41 per 100,000 (95% confidence interval: 1.26-1.57). Only China Beijing and Mexico RYVEMCE had total prevalences, which were significantly higher than this overall total prevalence. Some under-registration could influence the total prevalence in some programs. Liveborn cases represented 54.6% of total. Among monomelic cases (representing 65.2% of nonsyndromic amelia cases), both sides were equally involved, and the upper limbs (53.9%) were slightly more frequently affected. One of the most interesting findings was a higher prevalence of amelia among offspring of mothers younger than 20 years. Sixty-nine percent of the cases had MCA or syndromes. The most frequent defects associated with amelia were other types of musculoskeletal defects, intestinal, some renal and genital defects, oral clefts, defects of cardiac septa, and anencephaly.

A novel homozygous missense mutation (c.610G>A, p.Gly204Ser) in the WNT7A gene causes tetra-amelia in two Saudi families.

Fuhrmann syndrome and Al-Awadi/Raas-Rothschild/Schinzel (AA/RRS) phocomelia syndrome are rare autosomal recessive inherited disorders characterized by aplastic/hypoplastic nails with ectopic dorsal palms, absence of humeri, hypoplastic ulnae, and bowed short radii with the elbow joints present, shown to result from missense mutations in WNT7A (p.Ala109Thr and p.Arg292Cys). Here, we describe three affected individuals belonging to two related Saudi Arabian families. All three have a similar phenotype characterized by pelvic dysplasia and truncated lower limbs compatible with the clinical diagnosis of AA/RRS. The upper limbs were more variable: one patient individual had complete amelia, whereas the others had variable limb malformations and all had absence of nails and the ventralization of the palms/digits. All affected individuals were homozygous for a mutation in exon 4 of WNT7A (c.610G>A) resulted in substitution of a highly conserved glycine to serine (p.Gly204Ser) within the Wnt signature motif [C-K-C-H-G-V-S-G-S-C]. This report describes a third cases/family in the literature with variable phenotype of AA/RRS and Fuhrmann syndrome. Identification of this mutation further underlines the crucial involvement of WNT7A in the limb development. This novel missense homozygous mutation (p.Gly204Ser) in the WNT7A gene is a unique mutation in the degree of loss of function in the upper limb development which ranges from mild to complete absence of both upper limbs (amelia). Moreover, all three affected individuals had genitourinary anomalies, linking WNT7A function to genitourinary development.