Sperm disintegrins, egg integrins, and other cell adhesion molecules of mammalian gamete plasma membrane interactions

The cell-cell interactions that occur between sperm and egg involve not only the binding but also the fusion of the gamete plasma membranes. Numerous studies, carried out decades ago and more recently, have implicated several different molecules on both the sperm and egg as being involved in gamete membrane interactions. The sperm proteins that have received the most attention recently have homology to disintegrins, which are proteins in snake venoms that can interact with integrins. These sperm disintegrin-like proteins are members of a molecular family, known as ADAM's (for A Disintegrin and A Metalloprotease) or MDC's (for Metalloprotease, Disintegrin, Cysteine-rich). This review will focus on the molecules that have been implicated in mediating mammalian sperm-egg binding or the fusion of the gamete membranes. The molecules that will be discussed include three members of the ADAM/MDC family on sperm (fertilin alpha, fertilin beta, and cyritestin), integrins on eggs (alpha-6/beta-1 and others), and a number of other egg and sperm molecules, novel and characterized in other systems, that have been implicated in these processes.

The absence of a triphasic renovascular response by the multicalyceal kidney of the primate in reaction to acute, complete, unilateral, ureteric obstruction

The early renovascular response by the ipsilateral kidney to acute, total, unilateral, ureteric obstruction was investigated in the adult male chacma baboon (Papio ursinus). Complete occlusion was effected by ligating the ureter at the brim of the bony pelvis ("N"=10). Sham studies were enacted using the same method but the ureter was not obstructed ("N"=11). Haemodynamic reactions were monitored for 12 hours. Compared with the sham-occluded set, the renal pelvic pressures in the obstructed group were significantly increased (P<0.05) from the second hour of the inquiry. However, there were no significant differences in renal blood flow, either between or within the respective cohorts. In this study, the renovascular response to acute ureteric occlusion was similar to that displayed by the multicalyceal kidney of other species under identical conditions. This reaction was fundamentally different to that exhibited by the unicalyceal kidney under similar circumstances.

Molecular mechanisms of sperm-egg interactions and egg activation

The binding of acrosome reacted mammalian sperm to the egg plasma membrane initiates a series of signaling events in the egg, termed "egg activation", which lead to the completion of meiosis II and the initiation of a mitotic cell cycle. Many of these signaling events have characteristics of classical signal transduction events in somatic cells. Currently, there are two hypotheses for how sperm-induced egg activation is initiated. In the "receptor" hypothesis, the fertilizing sperm interacts with a specific egg surface receptor, and this interaction leads to signal transduction and effector activation. In the "fusion" hypothesis it is postulated that following fusion of the sperm and egg plasma membranes a soluble sperm-derived factor enters the egg's cytoplasm and activates pathways leading to egg activation. This chapter will provide an overview of the processes of cell-cell interaction and signal transduction leading to mammalian egg activation. It will concentrate on specific molecules proposed to be involved in sperm-egg interaction, signal transduction and effector mechanisms involved in egg activation, and a discussion of sperm-associated factors that have been implicated in egg activation.

Roles of the disintegrin domains of mouse fertilins alpha and beta in fertilization

Fertilin is a heterodimer of alpha and beta subunits, both of which are members of the ADAM (A Disintegrin and A Metalloprotease domain)/MDC (Metalloprotease-Disintegrin-Cysteine-rich) family of proteins. We have previously demonstrated that recombinant forms of the putative extracellular domains of mouse fertilin alpha and fertilin beta bind to mouse eggs and inhibit sperm-egg membrane binding. In this study, we examined the roles of the disintegrin domains of fertilins alpha and beta by producing recombinant forms of fertilins alpha and beta that included the disintegrin domains (alphaDCE and betaDCE) or that were truncated so that they lack the disintegrin domains (alphaCE and betaCE) and tested the abilities of these proteins to bind to eggs and to inhibit sperm-egg binding. Fertilin betaDCE was able to inhibit sperm-egg binding, but fertilin betaCE was relatively ineffective, indicating that the disintegrin domain of fertilin beta is required for interactions with egg binding sites and/or for proper protein folding. Fertilins alphaDCE and alphaCE both inhibited sperm-egg interactions, but fertilin alphaDCE tended to be more effective. Thus, the presence of the disintegrin domain in fertilin alphaDCE apparently enhanced the ability of this recombinant protein to inhibit sperm-egg binding, either by interacting with egg binding sites or by improving the efficiency of protein folding. These data also indicate that the other domains of the fertilin alpha extracellular region (cysteine-rich and/or epidermal growth factor-like repeat) have the ability to block sperm binding and suggest that these domains of fertilin alpha may participate in sperm-egg adhesion.

Mutations of the granulocyte-colony stimulating factor receptor in patients with severe congenital neutropenia are not required for transformation to acute myeloid leukaemia and may be a bystander phenomenon

Point mutations of the granulocyte-colony stimulating factor receptor (G-CSFR) resulting in an abnormally truncated receptor have been implicated in the pathogenesis of some cases of severe congenital neutropenia (SCN) and in the transformation of SCN to acute myeloid leukaemia (AML). We report here studies in 11 patients with SCN. No mutations were detected in the one patient who developed AML indicating that development of such mutations is not a prerequisite for transformation. Truncation mutations were detected in a minor percentage of transcripts from two other patients. In one patient the mutation has been constant at a low level (5-10% of total mRNA and 2/40 myeloid colonies) for 2 years. In the other patient the mutation was acquired, remained present at low levels for nearly 3 years and then spontaneously disappeared. Both patients had polyclonal haemopoiesis. We hypothesize that these mutations do not cause SCN, are randomly acquired with the mutant clone being expanded to detectable levels by high levels of exogenous or endogenous G-CSF, and may disappear by clonal succession. In a pre-leukaemic marrow the mutated subclone could achieve high levels, but this does not necessarily indicate a primary role of the mutant receptor in the leukaemogenic process.

A method for creating reversible ureteric obstruction in the primate

A technique has been developed for the establishment of a state of reversible, ureteric obstruction in the primate. Ten adult males had baseline 99mTc-DTPA renogram studies. A randomly selected ureter was totally occluded and obstruction confirmed on renogram. The occlusion was reversed and subsequent renograms confirmed recovery of activity in the obstructed kidneys of the eight animals who survived the reversal procedure. Seven were alive on conclusion of the study. Prevention of ureteric strictures was achieved with an intra-ureteric silastic tube. Autopsies demonstrated patency of every previously occluded ureter. This is the first study to be reported in primates, and the second overall, in which complete ureteric obstruction and its successful reversal has been confirmed on renogram using this surgical method. The technique is suitable for the study of the effect of reversible ureteric obstruction on renal function.

Predicting poor outcome in perforated peptic ulcer disease

BACKGROUND

Despite modern medications for peptic ulcers, patients frequently require emergency surgery for complications of ulcer disease. Many of these patients have coexisting medical problems which not only predispose to perforated ulcer disease, but also influence the clinical outcome. This study reviews the outcome of a group of patients with perforated ulcer disease and examines the influence of a range of comorbidity factors on the outcome.

METHODS

A retrospective chart review of all cases of perforated peptic occurring over a period of 9 years.

RESULTS

One hundred and forty-nine perforated peptic ulcers in 147 patients were diagnosed between 1987 and 1996. Coexisting malignancy, use of immunosuppressives or corticosteroids, pre-operative shock and admission to intensive care were all significantly associated with reperforation by univariate analysis. However, logistic regression analysis indicated that none of these factors independently predicted reperforation which, therefore, occurs as a multifactorial event with all the above factors contributing. Death from perforated ulcer disease was related to pre-operative shock, malignancy, admission to intensive care and reperforation when examined by univariate analysis. Furthermore, logistic regression analysis showed that coexisting malignancy and reperforation were significant predictors of mortality.

CONCLUSIONS

Perforated peptic ulcer disease remains a frequent clinical problem in patients with short dyspeptic histories, who may or may not have been using ulcerogenic medications. It is a significant cause of morbidity and mortality among an often aged and otherwise unwell group of patients. Patients with underlying malignant disease, who may be immunosuppressed with corticosteroids or cytotoxics, are at increased risk of dying from perforated ulcer disease. Reperforation of an ulcer, following simple closure or conservative treatment, is also highly predictive of increased mortality.

Characterization of the binding of recombinant mouse sperm fertilin alpha subunit to mouse eggs: evidence for function as a cell adhesion molecule in sperm-egg binding

Fertilin (previously known as PH-30) is a sperm protein that is a candidate molecule for mediating the binding and fusion of the sperm and egg plasma membranes. Fertilin is a heterodimer, with a beta subunit that has a region of homology to the disintegrin family of integrin ligands and an alpha subunit that has a region of homology to viral fusion peptides. It has been hypothesized that fertilin beta and alpha subunits mediate the interactions between sperm and egg plasma membranes, namely, binding and fusion, respectively. To address this hypothesis and to examine specifically the role of fertilin alpha in fertilization, we have expressed the predicted extracellular domain of mouse fertilin alpha as a bacterial fusion protein with maltose-binding protein. This fusion protein (hereafter referred to as recombinant fertilin alpha-EC) binds to the microvillar region of zona pellucida (ZP)-free eggs, the region of the membrane to which sperm bind. This binding is reduced in the absence of divalent cations and is supported by Ca2+, Mg2+, or Mn2+. Eggs that have been treated with chymotrypsin bind less recombinant fertilin alpha-EC than do untreated eggs, suggesting that a chymotrypsin-sensitive binding site for recombinant fertilin alpha-EC is present on egg surfaces. Binding to eggs is also affected by the method used to remove the ZP. Finally, recombinant fertilin alpha-EC inhibits the binding of sperm to eggs during in vitro fertilization of ZP-free eggs. These data are the first evidence to suggest that fertilin alpha can function as a cell adhesion molecule during fertilization, mediating the binding of sperm and egg plasma membranes.

Characterization of the binding of recombinant mouse sperm fertilin beta subunit to mouse eggs: evidence for adhesive activity via an egg beta1 integrin-mediated interaction

The sperm protein fertilin (also known as PH-30) is a candidate for mediating the interactions between sperm and egg plasma membranes. Fertilin is a heterodimer. The beta subunit, which has a region with homology to the family of integrin ligands known as disintegrins, has been hypothesized to be involved in the binding of sperm to the egg surface. To investigate this hypothesis and determine what role fertilin beta plays in fertilization, we have expressed the putative extracellular domain of mouse fertilin beta in bacteria as a fusion protein with maltose-binding protein (hereafter referred to as recombinant fertilin beta-EC) and used two assays to characterize its binding to mouse eggs. Immunocytochemistry was used to examine the localization of recombinant fertilin beta-EC binding. A luminometric assay was also developed to quantify levels of binding of recombinant fertilin beta-EC to single eggs. We find that recombinant fertilin beta-EC binds to the region of the plasma membrane of the egg to which sperm bind, thus providing the first direct evidence that fertilin beta has adhesive properties. Peptides corresponding to the disintegrin domain of fertilin beta reduce its binding to eggs, suggesting that this domain is at least partially involved in the recognition of fertilin beta by binding sites on the egg. Treatment of zona pellucida-free eggs with chymotrypsin reduces the ability of the eggs to support the binding of recombinant fertilin beta-EC, implicating an egg surface protein as a binding site for recombinant fertilin beta-EC. Binding of recombinant fertilin beta-EC to eggs is also reduced in the absence of divalent cations and is supported by 2.0 mM Ca2+, Mg2+, or Mn2+. Furthermore, eggs incubated in recombinant fertilin beta-EC prior to in vitro fertilization show reduced levels of sperm binding. Finally, we have examined the possible role of integrins on eggs as receptors for fertilin beta, since an anti-alpha6 integrin subunit monoclonal antibody, GoH3, has been shown to inhibit sperm binding (E. A. C. Almeida et al. (1995) Cell 81, 1095-1104). We find that: (a) an increased amount of GoH3 epitope on the egg surface does not correlate with an increased ability of the eggs to bind sperm or recombinant fertilin beta-EC; (b) the GoH3 antibody has virtually no inhibitory effect on recombinant fertilin beta-EC binding; and (c) recombinant fertilin beta-EC binding is reduced in the presence of anti-beta1 integrin antibodies. These results suggest that a beta1-containing integrin participates in the binding of recombinant fertilin beta-EC to mouse eggs.

The glomerular filtration rate, effective renal plasma flow, and renal blood flow in the adult male chacma baboon (Papio ursinus)

The radionuclide determination of glomerular filtration rate (GFR) and effective renal plasma flow (ERPF) has been validated in man, but not in the primate. GFR, ERPF, and renal blood flow (RBF) were measured in a group of 12 adult male chacma baboons using radiopharmaceuticals. GFR was determined using 99mtechnetium-labelled diethylenetriamine-pentacetic acid. ERPF was measured with 131iodine-labelled hippuran. RBF, body surface area, and kidney weights were calculated using standard formulae. GFR was 49 +/- 11 ml/min and ERPF was 237.9 +/- 54.2 ml/min. Calculated RBF was 430.7 +/- 111.9 ml/min and 507.4 +/- 138.4 ml/min/100 g of renal tissue. The results are in agreement with those obtained using more laborious nonradioisotopic techniques such as para-aminohippurate (PAH) and creatinine clearance and could serve as baseline normal values in the adult male chacma baboon.

Putrescine uptake by alveolar epithelial cell monolayers exhibiting differing transepithelial electrical resistances

Rat alveolar type II cells were isolated following elastase digestion and cultured on polycarbonate filters at various densities and in different media. Two days after seeding, the cells formed a monolayer on the filters which consisted predominantly of type II cells, these then de-differentiated to a alveolar type I-like cell monolayer by day 6. The seeding density and media utilized affected the transepithelial electrical resistance (TEER) generated by the monolayer. Only certain culture conditions allowed the production of a monolayer that mimics, putatively, the in vivo alveolar epithelium (TEER greater than 1000 omega cm2). Vmax and K(m) values for the uptake of putrescine by monolayers exhibiting low and high TEERs on day 6 were determined. The capacity of the putrescine uptake mechanisms was greater in cell monolayers exhibiting a high TEER than those exhibiting a low TEER, suggesting that the TEER does not only measure the "tightness" of the monolayer but contains an element representative of the viability of the cell monolayer. The selection of appropriate TEERs for cell culture investigations is discussed.

Characterization of the split hand/split foot malformation locus SHFM1 at 7q21.3-q22.1 and analysis of a candidate gene for its expression during limb development

Split hand/split foot malformation (SHFM) is a heterogeneous limb developmental disorder, characterized by missing digits and fusion of remaining digits. An autosomal dominant form of this disorder (SHFM1) has been mapped to 7q21.3-q22.1 on the basis of SHFM-associated chromosomal rearrangements. Utilizing a YAC contig across this region, we have defined a critical interval of 1.5 Mb by the analysis of six interstitial deletion patients and mapped the translocation breakpoints of seven ectrodactyly patients within the interval. To delineate the basic molecular defect underlying SHFM, we have searched for candidate genes in a 500 kb region containing five of the translocation breakpoints. Three genes were identified, two genes of the Distal-less (dii) homeobox gene family, DLX5 and DLX6 and a novel gene, which we named DSS1. DSS1 is predicted to encode a highly acidic polypeptide with no significant similarity to any known proteins but 100% amino acid sequence identify with its murine homolog (Dss1). Using RNA in situ hybridization analysis, we detected a tissue-specific expression profile for Dss1 in limb bud, craniofacial primordia and skin. A deficiency in expression of Dss1, DLX5 and/or DLX6 during development may explain the SHFM phenotypes.

A second autosomal split hand/split foot locus maps to chromosome 10q24-q25

Ectrodactyly (split hand/split foot malformation, SHSF) is a human limb malformation characterized by absent central digital rays, deep median cleft, and syndactyly of remaining digits. The disorder is genetically heterogeneous, with at least two loci thus far determined: an autosomal locus at 7q21 designated SHFM1 and an X-linked locus at Xq26 designated SHFM2. Cytogenetic analysis of sporadic SHSF patients and linkage studies in extended pedigrees both suggest more than one autosomal locus exists. We report a novel SHSF locus suggested by a stillborn infant with ectrodactyly and other malformations who inherited an unbalanced translocation resulting in monosomy 4p15.1-4pter and trisomy for 10q25.2-qter. To investigate 10q25 as a possible split hand/split foot locus, microsatellite markers spanning 52 cM of 10q were utilized for linkage analysis of a large autosomal dominant SHSF pedigree in which the region encompassing SHFM1 previously was excluded as containing the causative mutation. The marker D10S583 was fully informative in the family, giving a maximum LOD score of 4.21 at recombination theta = 0.00. Recombination haplotypes define the 9 cM region between D10S541 and D10S574 as inclusive for this second autosomal SHSF locus, for which we propose the designation SHFM3.

Mouse sperm-egg plasma membrane interactions: analysis of roles of egg integrins and the mouse sperm homologue of PH-30 (fertilin) beta

The guinea pig sperm protein, PH-30 (also known as fertilin), is postulated to participate in the interaction between the sperm and egg plasma membranes. The beta subunit of guinea pig PH-30 (gpPH-30 beta) contains a domain with homology to disintegrins, snake venom proteins that bind to integrins via an integrin-binding domain containing the tripeptide RGD. This raises the question of whether an egg integrin serves as a receptor for PH-30. Although mouse eggs express integrin subunits, their role in mouse fertilization is unresolved. Therefore, we examined fertilization for two different hallmarks of integrin function, namely, dependence of ligand binding on divalent cations and the ability to inhibit ligand binding with RGD peptides. We demonstrate that sperm binding to zona pellucida-free eggs is supported by Ca2+, Mg2+, or Mn2+. Ca2+ was necessary and sufficient for sperm-egg fusion, with 2.5 mM Ca2+ being the most effective concentration. In addition, fertilization could be partially inhibited with various RGD peptides, which caused a decrease in sperm-egg fusion by 30–58%. This partial inhibition of fusion with RGD peptides prompted the cloning of the mouse homologue of gpPH-30 beta (hereafter referred to as mPH-30 beta) to determine if it possessed the tripeptide RGD or a different amino acid sequence in its disintegrin domain. mPH-30 beta, which is expressed during meiotic and post-meiotic phases of spermatogenesis, shares significant similarities to gpPH-30 beta throughout the length of the molecule, from the signal sequence to the cytoplasmic tail. The full-length deduced amino acid sequence of mPH-30 beta. The disintegrin domain of mPH-30 beta has the tripeptide QDE (instead of RGD) in its cell recognition region. Peptides containing this QDE sequence decrease the binding and fusion of sperm with zona pellucida-free eggs by approximately 70%, suggesting that the disintegrin domain of mPH-30 beta participates in the interaction between sperm and egg membranes.

Kostmann's disease, recombinant HuG-CSF, monosomy 7 and MDS/AML

Monosomy 7 (Mo7) and leukaemia predisposition are associated with Kostmann's disease (KD). The recent introduction of long-term recombinant HuG-CSF treatment in patients with KD, whilst showing significant reductions in infectious complications and improved quality of life, might also be associated with an increased risk of developing karyotypic abnormalities, myelodysplasia (MDS) and acute myeloid leukaemia (AML). We describe a case of an identical twin with probable autosomal dominant KD who developed anaemia, Mo7/MDS and AML at 18, 30 and 50 months respectively from starting r-metHuG-CSF (filgrastim) treatment. Further patient analyses are required to establish the natural history of KD and to determine what role, if any, filgrastim plays in altering the pathobiology of this disorder.

A germline substitution in the human MSH2 gene is associated with high-grade dysplasia and cancer in ulcerative colitis

BACKGROUND & AIMS

The DNA mismatch repair gene human MSH2 shows a germline mutation in certain family members with hereditary nonpolyposis colorectal cancer. There is an increased risk of colorectal cancer in patients with ulcerative colitis (UC) with extensive disease of > 8 years' duration; however, specific constitutional predisposing genetic abnormalities have not yet been identified.

METHODS

A germline human MSH2 abnormality was sought in patients with UC with high-grade dysplasia or carcinoma.

RESULTS

After direct sequencing of exon 13 and flanking regions of human MSH2, a germline T to C substitution was shown at the -6 intronic splice acceptor site of exon 13. This substitution was found in 14 of 53 patients with UC with high-grade dysplasia or carcinoma (26%) compared with 4 of 36 high-risk patients with UC without dysplasia or cancer (11%) (P < or = 0.04) and in 7 of 80 healthy adult blood donors (9%) (P < or = 0.003). The patients with UC who had the substitution were three times more likely to develop neoplasia than patients with UC who did not carry it.

CONCLUSIONS

An intronic splice-site substitution in the human MSH2 gene is present in the general population but may predispose to cancer in the setting of UC.

Familial pancreatic adenocarcinoma: association with diabetes and early molecular diagnosis

We report a large pedigree in which pancreatic cancer is inherited in an autosomal dominant fashion. Diabetes and exocrine insufficiency was observed in all family members who eventually developed pancreatic cancer. The presence of diabetes, often years before the diagnosis of cancer, allowed identification of those people who had inherited the predisposing allele and who were thus at high risk for the development of malignancy. This family shows that genetic factors can have a striking effect on the development of pancreatic malignancy and diabetes mellitus. Moreover, preclinical diagnosis of pancreatic cancer in family members provided a unique opportunity to study early molecular changes that accompany the development of human pancreatic cancer. Finally, the molecular approach applied here to the early diagnosis of pancreatic cancer may prove valuable in this family for identification of subjects at risk.

Asp187Asn mutation of gelsolin in an American kindred with familial amyloidosis, Finnish type (FAP IV)

Familial amyloidosis, Finnish type (FAP-IV) was identified clinically in an American kindred with Scandinavian ancestry. A polymerase chain reaction (PCR)-based DNA diagnostic assay was used to identify a G-to-A mutation at position 654 of the gelsolin cDNA (G654A) in this family. Molecular diagnostic testing demonstrated the mutation in individuals in three generations--the clinically affected proband, here deceased clinically affected father, and her presumably affected presymptomatic child. This report represents a rare example of FAP IV and the G654A mutation identified in a family outside Finland. The disease-associated haplotype was similar to that observed in Finnish FAP IV families (suggesting common distant ancestry).

Identification and localization of integrin subunits in oocytes and eggs of the mouse

Results of a recent study have implicated egg integrins in sperm binding to the egg plasma membrane (Blobel et al., 1991: Nature 356:248-252). In this report, immunoprecipitation was used to identify, and confocal immunofluorescence microscopy was used to localize, several different integrin subunits in mouse eggs. Antibodies to alpha 2, alpha 5, alpha v, and beta 1 subunits, as well as antibodies to the fibronectin receptor (FNR; alpha 5 beta 1 and/or alpha 3 beta 1) and vitronectin receptor (VNR; alpha v beta 3 and/or alpha v beta 5), detect polypeptides of the appropriate molecular weights following immunoprecipitation. beta 1 is localized preferentially to either the microvillar or amicrovillar membrane/cortical regions of eggs, and these asymmetric localizations depend on the antibody used. Proteins recognized by anti-FNR antibodies are localized preferentially to the amicrovillar membrane/cortical region. Germinal vesicle-intact oocytes display a symmetric plasma membrane distribution using beta 1 and FNR antibodies, and the asymmetric distribution develops as a consequence of oocyte maturation and is clearly observed by metaphase I. In contrast to the membrane localization of these integrin subunits, alpha 2, alpha 5, and VNR are predominantly localized in the cytoplasm of both oocytes and eggs. In the oocyte, each of these integrin subunits is uniformly distributed throughout the cytoplasm. Oocyte maturation is associated with a redistribution of alpha 5 and VNR, leading to an asymmetric cytoplasmic distribution with an increased localization towards the spindle. alpha v, which is localized in the plasma membrane/cortex of both oocytes and eggs, does not show such a change during oocyte maturation. Results of these experiments are discussed in the context of a role for integrins in mediating sperm plasma membrane-egg plasma membrane interactions leading to egg activation.

Split foot and developmental retardation associated with a deletion of three microsatellite markers in 7q21.2-q22.1

A deletion of 7q21.2-q22.1 has been found in a patient with split foot and developmental retardation. Molecular analysis using polymerase chain reaction (PCR) showed deletion of three microsatellite markers, D7S527, D7S479 and D7S554, in the patient's paternal chromosome. These results pinpoint the critical region for an ectrodactyly locus (SHFD1) on chromosome 7.

A quick embedding method for light microscopy and image analysis of cotton fibers

A quick embedding method using UV polymerization of methacrylate plastic has been devised for embedding fibers encased in a polyvinyl chloride tube. The resulting embedments are suitable for light microscopy and image analysis.

A contiguous gene deletion syndrome at 7q21-q22 and implications for a relationship between isolated ectrodactyly and syndromic ectrodactyly

Ectrodactyly is a genetically heterogeneous human limb developmental malformation with an autosomal locus at 7q21 designated SHFD1. We report a patient with ectrodactyly and a small interstitial deletion of 7q21, detected by high resolution karyotype, which provides additional evidence for the existence of an ectrodactyly gene in this region and further restricts the size of the critical region containing SHFD1. A review of previously published patients with ectrodactyly and similar deletions suggests a contiguous gene deletion syndrome at 7q21-q22 which consists of ectrodactyly, growth retardation, developmental delay, hypertelorism, ear malformation, components of the Robin sequence, and GU abnormalities. Moreover, the clinical, genetic, and cytogenetic similarities of a number of multiple congenital anomaly syndromes which include ectrodactyly as just one component lead us to propose that a common genetic basis may underlie many of these syndromes. Thus, evaluation for related physical anomalies and high resolution cytogenetic studies are indicated in patients with ectrodactyly.