A classification system for split-hand/ foot malformation (SHFM): A proposal based on 3 pedigrees with WNT10B mutations

SHFM6 (OMIM 225300) is caused by WNT10B pathogenic variants (12q13.12). It is one of the rarest forms of SHFM; with only seven pathogenic variants described in the world literature. Furthermore, it has not been determined if SHFM6 has specific phenotypic characteristics. In this paper, we present a case series of three unrelated families with SHFM6 caused by three novel WNT10B pathogenic variants. The index patient of the first family was homozygous for the nonsense variant c.676C > T (p.Arg226*) in the WNT10B gene. The index case of the second family had a homozygous splice variant c.338-1G > C in the WNT10B gene. Finally, the index case of the third family carried two different variants in the WNT10B gene: A nonsense variant (p.Arg226*), and a missense variant (p.Gln86Pro). The latter represents the first compound heterozygous pathogenic variant related to SHFM6. We also offer a classification system for the hand/foot defects to illustrate the specific phenotypic characteristics of SHFM6. Based on this classification and a review of all previously reported cases, we demonstrate that SHFM6 caused by WNT10B pathogenic variants have the following characteristics: more severe feet defects (compared to the hand defects), polydactyly, severe flexion digital contractures, and phalangeal dysplasia.

Postaxial limb hypoplasia (PALH): the classification, clinical features, and related developmental biology

Postaxial limb hypoplasia (PALH) is a group of nonhereditary diseases with congenital lower limb deficiency affecting the fibular ray, including fibular hemimelia, proximal femoral focal deficiency, and tarsal coalition. The etiology and the developmental biology of the anomaly are still not fully understood. Here, we review the previous classification systems, present the clinical features, and discuss the developmental biology of PALH.

Elements of morphology: standard terminology for the hands and feet

An international group of clinicians working in the field of dysmorphology has initiated the standardization of terms used to describe human morphology. The goals are to standardize these terms and reach consensus regarding their definitions. In this way, we will increase the utility of descriptions of the human phenotype and facilitate reliable comparisons of findings among patients. Discussions with other workers in dysmorphology and related fields, such as developmental biology and molecular genetics, will become more precise. Here we introduce the anatomy of the hands and feet and define and illustrate the terms that describe the major characteristics of the hands and feet.

Abnormal urethra formation in mouse models of split-hand/split-foot malformation type 1 and type 4

Urogenital birth defects are one of the common phenotypes observed in hereditary human disorders. In particular, limb malformations are often associated with urogenital developmental abnormalities, as the case for Hand-foot-genital syndrome displaying similar hypoplasia/agenesis of limbs and external genitalia. Split-hand/split-foot malformation (SHFM) is a syndromic limb disorder affecting the central rays of the autopod with median clefts of the hands and feet, missing central fingers and often fusion of the remaining ones. SHFM type 1 (SHFM1) is linked to genomic deletions or rearrangements, which includes the distal-less-related homeogenes DLX5 and DLX6 as well as DSS1. SHFM type 4 (SHFM4) is associated with mutations in p63, which encodes a p53-related transcription factor. To understand that SHFM is associated with urogenital birth defects, we performed gene expression analysis and gene knockout mouse model analyses. We show here that Dlx5, Dlx6, p63 and Bmp7, one of the p63 downstream candidate genes, are all expressed in the developing urethral plate (UP) and that targeted inactivation of these genes in the mouse results in UP defects leading to abnormal urethra formation. These results suggested that different set of transcription factors and growth factor genes play similar developmental functions during embryonic urethra formation. Human SHFM syndromes display multiple phenotypes with variations in addition to split hand foot limb phenotype. These results suggest that different genes associated with human SHFM could also be involved in the aetiogenesis of hypospadias pointing toward a common molecular origin of these congenital malformations.

Prenatal ultrasonographical features of limb body wall complex: a review of etiopathogenesis and a new classification

Limb body wall complex is a spectrum of multiple severe anomalies. The etiopathogenesis and clinical classification are still under discussion. In our article, while reviewing previous etiopathogenetical hypothesis, we propose a new clinical classification regarding embryological theories and pheneotypical features. According to the Van Allen diagnostic criteria, the findings of 6 affected fetuses are presented. Prenatal diagnosis was performed in 5 of 6 cases. Craniofacial malformations were present in only 1 case. Thoracic defect and abdominoschisis (either infraumbilical or supraumbilical) associated with visceral eventration, placental-umbilical cord anomalies, and limb defects were detected in the other 5 cases. Aberrant development of each of the 4 embryonic folds (cephalic, 2 lateral abdominal, and caudal) associated with faulty umbilical ring development and placental formation were considered responsible for development of various malformations. In previous clinical classifications, existence or absence of the craniofacial malformation was utilized as an unique discriminating criterion while multiple anomalies exist. In this report, we propose a new clinical classification concerning almost all anomalies caused by defective placental attachment and maldevelopment of the 4 folds.

[Anatomical basis of classifications of congenital limbs deficiencies]

The wide range of the congenital skeletal limb deficiencies caused difficulties with their classification. We present the most fundamentally and the most common classifications of the congenital skeletal defects.

A morpho-etiological description of congenital limb anomalies

BACKGROUND

Limb anomalies rank behind congenital heart disease as the most common birth defects observed in infants. More than 50 classifications for limb anomalies based on morphology and osseous anatomy have been drafted over the past 150 years. The present work aims to provide a concise summary of the most common congenital limb anomalies on a morpho-etiological basis.

PATIENTS AND METHODS

In a retrospective study, 70 newborns with anomalies of the upper and/or lower limbs were ascertained through clinical examination, chromosomal analysis, skeletal surveys and other relevant investigations.

RESULTS

Fetal causes of limb anomalies represented 55.8% of the cases in the form of 9 cases (12.9%) with chromosomal aberrations (trisomy 13, 18 and 21, duplication 13q and deletion 22q) and 30 cases (42.9%) with single gene disorders. An environmental etiology for limb anomalies was diagnosed in 11 cases (15.7%) as amniotic band disruption, monozygotic twin with abnormal circulation, vascular disruption (Poland sequence, sirenomelia and general vascular disruption) and an infant with a diabetic mother. Twenty cases (28.5%) had limb anomalies as part of sporadic syndromes of unknown etiology.

CONCLUSIONS

The morpho-etiological work-up of limb anomalies adopted in the present study is valuable for detecting the cause of the anomaly and is crucial for its prevention. Prevention can be achieved by proper genetic counseling, which includes recurrence risk estimation and prenatal diagnosis.

Descriptive epidemiology of limb reduction deformities in Hawaii, 1986-2000

The relationship between limb reduction deformities and clinical and demographic factors in Hawaii during 1986-2000 were examined using population-based birth defects program data. The limb defect rate was highest with maternal age less than 20 years, and the defect was more common among males. Among racial/ethnic groups, Pacific Islanders and Filipinos had higher rates than whites and Far East Asians.

Human limb malformations; an approach to the molecular basis of development

Analysis of human inherited limb malformations and of mouse mutants copying individual human mutations team up to promote the understanding of vertebrate limb development as a model for molecular regulatory interactions in animals. The strength of the human genetic contribution lies in the increasingly complete information on the human genome, transcriptome and proteome, as well as in the wealth of individual mutations interfering with limb development available for study. Based on the strong fundament of the human genome project, mapping and identification of novel genes associated with limb defects extends considerably the range of candidates beyond the repertoire of developmental genes and pathways known from animals. Attempts to correlate genotype and phenotype uncover a very broad range of genetic heterogeneity, i.e. different genes underlying the same phenotype, or allelic heterogeneity between families, i.e. clinically distinct phenotypes associated with mutations affecting the same gene. Mechanisms other than simple Mendelian inheritance have to be taken into consideration. Phenotypic variability within families might be explained by different modifying genes or environmental influence, whereas asymmetry of limb defects within one patient may be caused by epigenetic factors, such as somatic mosaicism or X-inactivation, or by non-genetic factors. The intimate knowledge of the genes and events governing limb pattern formation in humans and animals will elucidate the regulatory interactions underlying normal and pathological development, homeostasis, and repair, and thus propose targets for preventive measures and novel approaches to therapeutic intervention in the new era of molecular medicine.

Leaping lopsided: a review of the current hypotheses regarding etiologies of limb malformations in frogs

Recent progress in the investigation of limb malformations in free-living frogs has underlined the wide range in the types of limb malformations and the apparent spatiotemporal clustering of their occurrence. Here, we review the current understanding of normal and abnormal vertebrate limb development and regeneration and discuss some of the molecular events that may bring about limb malformation. Consideration of the differences between limb development and regeneration in amphibians has led us to the hypothesis that some of the observed limb malformations come about through misdirected regeneration. We report the results of a pilot study that supports this hypothesis. In this study, the distal aspect of the right hindlimb buds of X. laevis tadpoles was amputated at the pre-foot paddle stage. The tadpoles were raised in water from a pond in Minnesota at which 7% of surveyed newly metamorphosed feral frogs had malformations. Six percent (6 of 100) of the right limbs of the tadpoles raised in pond water developed abnormally. One truncated right limb was the only malformation in the control group, which was raised in dechlorinated municipal water. All unamputated limbs developed normally in both groups. Three major factors under consideration for effecting the limb malformations are discussed. These factors include environmental chemicals (primarily agrichemicals), encysted larvae (metacercariae) of trematode parasites, and increased levels of ultraviolet light. Emphasis is placed on the necessary intersection of environmental stressors and developmental events to bring about the specific malformations that are observed in free-living frog populations.

On the symmetry of limb deficiencies among children with multiple congenital anomalies

In humans, unpaired organs are placed in a highly ordered pattern along the left-right axis. As indicated by animal studies, a cascade of signaling molecules establish left-right asymmetry in the developing embryo. Some of the same genes are involved also in limb patterning. To provide a better insight into the connection between these processes in humans, we analysed the symmetry of limb deficiencies among infants with multiple congenital anomalies. The study was based on data collected by the International Clearinghouse for Birth Defects Monitoring Systems (ICBDMS). Registries of the ICBDMS provided information on infants who, in addition to a limb deficiency, also had at least one major congenital anomaly in other organ systems. We reviewed 815 such cases of which 149 cases (18.3 %) were syndromic and 666 (81.7 %) were nonsyndromic. The comparisons were made within the associated limb deficiencies, considering the information on symmetry, using a comparison group with malformations associated not involved in the index association. Among the non-syndromic cases, the left-right distribution of limb deficiencies did not differ appreciably between limb deficiency subtypes (e.g., preaxial, transverse, longitudinal). The left-right distribution of limb anomalies did not differ among most types of non-limb anomalies, though a predominance of left-sided limb deficiencies was observed in the presence of severe genital defects - odds ratio [OR], 2.6; 95 % CI, 1.1-6.4). Limb deficiencies (LDs) were more often unilateral than bilateral when accompanied by gastroschisis (OR, 0.1) or axial skeletal defects (OR, 0.5). On the contrary, LDs were more often bilateral than unilateral when associated with cleft lip with or without cleft palate (OR, 3.9) or micrognathia (OR, 2.6). Specifically, we found an association between bilateral preaxial deficiencies and cleft lip, bilateral amelia with gastroschisis and urinary tract anomalies, and bilateral transverse deficiencies and gastroschisis and axial skeleton defects. Of 149 syndromic cases, 62 (41.6 %) were diagnosed as trisomy 18. Out of the 30 cases of trisomy 18 with known laterality, 20 cases were bilateral. In the remainder the right and left sides were equally affected. Also, in most cases (74.4 %) only the upper limbs were involved. In conclusion the left-right distribution of limb deficiencies among some non-limb anomalies may suggest a relationship between the development of the limb and the left-right axis of the embryo.

[Mass anomalies of the extremities in anurans]

The author analyses literature data on anomalies of limbs in Anura. It is shown that published data is usually not enough to discuss either conditions of appearance or the causes of anomalies. Traditional statistical methods does not adequately characterise the frequency of anomalies. The author suggests a new criteria for ascertaining the fact of appearance of mass anomalies. A number of experimental data don't correspond to current theoretical ideas about the nature of anomalies. It is considered to distinguish "background" and "mass" anomalies. "Background" anomalies can not be a good indicator of unfavourable condition of development.

Metaphyseal anadysplasia type II: a new regressive metaphyseal dysplasia

We report on six unrelated children, three boys and three girls, with a metaphyseal dysplasia of early onset and spontaneous regressing evolution. During the first months of life the children present with enlargement of costochondral junctions and knobby wrists. On radiographs the metaphyseal changes of the knees are specific with fine irregularities. The femoral necks are blurred but not hypoplastic. The stature is not affected and there are no metabolic abnormalities. The radiographic findings regress during growth and the abnormalities disappear after the age of ten years. These metaphyseal changes and their mode of inheritance are different from previous cases described as anadysplasia. We propose therefore to delineate this syndrome as a new type of regressive metaphyseal dysplasia and to name it anadysplasia type II.

Oromandibular-limb hypogenesis syndromes: a case of aglossia with an intraoral band

Oromandibular and limb syndromes feature primarily in sporadic case reports because of their low incidence. They include Moebius syndrome, aglossia-adactylia syndrome, Hanhart syndrome, glossopalatine ankylosis syndrome, limb deficiency-splenogonadal fusion syndrome and Charlie M. syndrome. There is confusion in the classification of these patients because of the associated anomalies and the frequency of overlapping features. This paper presents a patient with oromandibular malformations associated with major defects in the upper and lower limbs. Aglossia in the presence of an intraoral band is a peculiar association demanding classification. This case confirms that aglossia-adactylia syndrome and the glossopalatine ankylosis syndrome are variants along a spectrum.

Correlated heart/limb anomalies in Mendelian syndromes provide evidence for a cardiomelic developmental field

Coordinated development of heart and limbs is suggested by a review of human abortus, chromosomal, and teratogenic syndromes, and characterized by an analysis of Mendelian disorders that affect the limbs, heart, or both (672, 202, or 107, respectively). Mendelian syndromes with altered limb patterns often include cardiac anomalies, as shown by limb duplications (34%), deficiencies (30%), hypoplasias (23%), or dysplasias (9.3%). Syndromes with particular cardiac anomalies, illustrated by VSD (85%) or ASD (90%), frequently include limb defects. Positional correlations of anterior (preaxial/conotruncal), posterior (postaxial/atrial), or lateral (mirror hand/atrial isometry) heart/limb anomalies are consistent with the existence of a cardiomelic developmental field. Vertebrate comparisons suggest an early D-V limb-heart gradient, influenced by the neural crest, with distal limb segments (80% of syndromic defects) at its dorsal extreme. The proposed cardiomelic field relates the genetic heterogeneity of disorders such as Holt-Oram syndrome to a cascade of molecules, including the brachyury, sonic hedgehog, bone morphogenetic protein, retinoic acid receptor, and transforming growth factor-beta families.