[Molecular genetics of Hirschsprung disease: a model of multigenic neurocristopathy]

Hirschsprung's disease (HSCR, aganglionic megacolon) is a frequent congenital malformation regarded as a multigenic neurocristopathy. Three susceptibility genes have been recently identified in HSCR, namely the RET proto-oncogene, the endothelin B receptor (EDNRB) gene, and the endothelin 3 (EDN3) gene. RET gene mutations were found in significant proportions of familial (50%) and sporadic (15-20%) HSCR, while homozygosity for EDNRB or EDN3 mutations accounted for the rare HSCR-Waardenburg syndrome (WS) association. More recently, heterozygous EDNRB an EDN3 missense mutations have been reported in isolated HSCR patients. Some of these results were obtained after the identification of mouse genes whose natural or site-directed mutations resulted in megacolon and coat color spotting. There is also conclusive evidence for the involvement of other independent loci in HSCR. In particular, the recent identification of neurotrophic factors acting as RET ligands (GDNF and Neurturin) provide additional candidate genes for HSCR. The dissection of the genetic etiology of HSCR disease may then provide a unique opportunity to distinguish between a polygenic and a genetically heterogeneous disease, thereby helping to understand other complex disorders and congenital malformations hitherto considered as multifactorial in origin. Finally, the study of the molecular bases of HSCR is also a step towards the understanding of developmental genetics of the enteric nervous system giving support to the role of the tyrosine kinase and endothelin-signaling pathways in the development of neural crest-derived enteric neurons in human.

Clinical features of 52 neonates with hyperinsulinism

BACKGROUND

Neonatal hyperinsulinemic hypoglycemia is often resistant to medical therapy and is often treated with near-total pancreatectomy. However, the pancreatic lesions may be focal and treatable by partial pancreatic resection.

METHODS

We studied 52 neonates with hyperinsulinism who were treated surgically. The type and location of the pancreatic lesions were determined by preoperative pancreatic catheterization and intraoperative histologic studies. Partial pancreatectomy was performed in infants with focal lesions, and near-total pancreatectomy was performed in those with diffuse lesions. The postoperative outcome was determined by measurements of plasma glucose and glycosylated hemoglobin and by oral glucose-tolerance tests.

RESULTS

Thirty neonates had diffuse beta-cell hyperfunction, and 22 had focal adenomatous islet-cell hyperplasia. Among the latter, the lesions were in the head of the pancreas in nine, the isthmus in three, the body in eight, and the tail in two. The clinical manifestations were similar in both groups. The infants with focal lesions had no symptoms of hypoglycemia and had normal preprandial and postprandial plasma glucose and glycosylated hemoglobin values and normal results on oral glucose-tolerance tests after partial pancreatectomy (performed in 19 of 22 neonates). By contrast, after near-total pancreatectomy, 13 of the patients with diffuse lesions had persistent hypoglycemia, type 1 diabetes mellitus developed in 8, and hyperglycemia developed in another 7; overall, only 2 patients with diffuse lesions had normal plasma glucose concentrations in the first year after surgery.

CONCLUSIONS

Among neonates with hyperinsulinism, about half may have focal islet-cell hyperplasia that can be treated with partial pancreatectomy. These neonates can be identified through pancreatic catheterization and intraoperative histologic studies.

Loss of imprinted genes and paternal SUR1 mutations lead to hyperinsulinism in focal adenomatous hyperplasia

Two types of histopathological lesions, a focal adenomatous hyperplasia of islet cells of the pancreas in about 30% of operated sporadic cases, and a diffuse form can be observed in congenital hyperinsulinism, or Persistent Hyperinsulinemic Hypoglycemia of Infancy (PHHI). In sporadic focal forms, specific losses of maternal alleles (LOH) of the imprinted chromosomal region 11p15, restricted to the hyperplastic area of the pancreas, were observed. Similar mechanisms are observed in embryonal tumors and in the Beckwith-Wiedemann syndrome which is also associated with neonatal but transient hyperinsulinism. However this region also contains the sulfonylurea receptor (SUR1) gene and the inward rectifying potassium channel subunit (KIR6.2) gene, involved in recessive familial forms of PHHI, but not known to be imprinted. We now report somatic reduction to hemizygosity or homozygosity of a paternal SUR1 constitutional heterozygous mutation, in five patients with a focal form of PHHI. Thus this somatic event (LOH) which leads both to b cell proliferation and to hyperinsulinism can be considered as the somatic equivalent, restricted to a microscopic focal lesion, of constitutional uniparental disomy associated with unmasking of a heterozygous parental mutation leading to a somatic recessive disorder.

Evaluation of gonadal function in 107 intersex patients by means of serum antimüllerian hormone measurement

Fetal male sexual differentiation is driven by two testicular hormones: testosterone (synthesized by interstitial Leydig cells) and antimüllerian hormone (AMH; produced by Sertoli cells present in the seminiferous tubules). Intersex states result either from gonadal dysgenesis, in which both Leydig and Sertoli cell populations are affected, or from impaired secretion or action of either testosterone or AMH. Until now, only Leydig cell function has been assessed in children with ambiguous genitalia, by means of testosterone assay. To determine whether serum AMH would help in the diagnosis of intersex conditions, we assayed serum AMH levels in 107 patients with ambiguous genitalia of various etiologies. In XY patients, AMH was low when the intersex condition was caused by abnormal testicular determination (including pure and partial gonadal dysgenesis) but was normal or elevated in patients with impaired testosterone secretion, whereas serum testosterone was low in both groups. AMH was also elevated during the first year of life and at puberty in intersex states caused by androgen insensitivity. In 46,XX patients with a normal male phenotype or ambiguous genitalia, in whom the diagnosis of female pseudohermaphroditism had been excluded, serum AMH levels higher than 75 pmol/L were indicative of the presence of testicular tissue and correlated with the mass of functional testicular parenchyma. In conclusion, serum AMH determination is a powerful tool to assess Sertoli cell function in children with intersex states, and it helps to distinguish between defects of male sexual differentiation caused by abnormal testicular determination and those resulting from isolated impairment of testosterone secretion or action.

[Persistent hyperinsulinemic hypoglycemia in the newborn and infants]

Persistent hyperinsulinemic hypoglycaemia of infancy (PHHI) is the most frequent cause of hypoglycaemia in infancy. Clinical presentation is heterogeneous, with variable onset of hypoglycaemia and response to diazoxide, and presence of sporadic or familial forms. Underlying histopathological lesions can be focal or diffuse. Focal lesions are characterised by focal hyperplasia of pancreatic islet-like cells, whereas diffuse lesions implicate the whole pancreas. The distinction between the two forms is important because surgical treatment and genetic counselling are radically different. Focal lesions correspond to somatic defects which are totally cured by limited pancreatic resection, whereas diffuse lesions require a subtotal pancreatectomy exposing to high risk of diabetes mellitus. Diffuse lesions are due to functional abnormalities involving several genes and different transmission forms. Recessively inherited PHHI have been attributed to homozygote mutations for the beta-cell sulfonylurea receptor (SUR1) or the inward-rectifying potassium-channel (Kir6.2) genes. Dominantly inherited PHHI can implicate the glucokinase gene, particularly when PHHI is associated with diabetes, the glutamate dehydrogenase gene when hyperammonaemia is associated, or another locus.

Paternal mutation of the sulfonylurea receptor (SUR1) gene and maternal loss of 11p15 imprinted genes lead to persistent hyperinsulinism in focal adenomatous hyperplasia

Congenital hyperinsulinism, or persistent hyperinsulinemic hypoglycemia of infancy (PHHI), is a glucose metabolism disorder characterized by unregulated secretion of insulin and profound hypoglycemia. From a morphological standpoint, there are two types of histopathological lesions, a focal adenomatous hyperplasia of islet cells of the pancreas in approximately 30% of operated sporadic cases, and a diffuse form. In sporadic focal forms, specific losses of maternal alleles (LOH) of the imprinted chromosomal region 11p15, restricted to the hyperplastic area of the pancreas, were observed. Similar mechanisms are observed in embryonal tumors and in the Beckwith-Wiedemann syndrome (BWS), also associated with neonatal but transient hyperinsulinism. However, this region also contains the sulfonylurea receptor (SUR1) gene and the inward rectifying potassium channel subunit (KIR6.2) gene, involved in recessive familial forms of PHHI, but not known to be imprinted. Although the parental bias in loss of maternal alleles did not argue in favor of their direct involvement, the LOH may also unmask a recessive mutation leading to persistent hyperinsulinism. We now report somatic reduction to hemizygosity or homozygosity of a paternal SUR1 constitutional heterozygous mutation in four patients with a focal form of PHHI. Thus, this somatic event which leads both to beta cell proliferation and to hyperinsulinism can be considered as the somatic equivalent, restricted to a microscopic focal lesion, of constitutional uniparental disomy associated with unmasking of a heterozygous parental mutation leading to a somatic recessive disorder.

[Mutations of the endothelin-3 gene in isolated and syndromic forms of Hirschsprung disease]

AIMS AND METHODS

Hirschsprung's disease is a frequent congenital malformation regarded as a multigenic neurocristopathy. Three susceptibility genes have been identified in Hirschsprung's disease, namely the RET proto-oncogene, the Glial cell line-Derived Neurotrophic Factor and the endothelin B receptor. A total of 174 probands with isolated Hirschsprung's disease (59 familial, 117 sporadic cases), and 4 patients with associated Waardenburg's syndrome and Hirschsprung's disease (1 familial, 3 sporadic cases) were screened for mutations in the coding sequence of the endothelin 3 gene. The coding sequence of the endothelin 3 gene was analyzed for point mutations, using a combination of SSCP analysis and direct DNA sequencing.

RESULTS

Two heterozygous mutations (A17T and A224T) were identified in two patients with isolated Hirschsprung's disease. Two homozygous truncations mutations (E55X and GC262->T) were identified in patients with the Waardenburg's syndrome/Hirschsprung's disease association.

CONCLUSION

The present data give further support to the role of the endothelin-signaling pathway in the development of neural crest-derived enteric neurons. They also suggest that either recessive and weakly penetrant dominant alleles could occur at the EDN3 locus, depending on the nature of the mutation.

Neonatal hyperinsulinemic hypoglycemia: heterogeneity of the syndrome and keys for differential diagnosis

The two major forms of infantile persistent hyperinsulinemic hypoglycemia require different treatments, but are difficult to differentiate during surgery. Indeed, one is characterized by focal adenomatous hyperplasia often macroscopically invisible, whereas the other consists of a diffuse, but discreet, beta-cell abnormality. We evaluated, in a large series of persistent hyperinsulinemic hypoglycemia, the reliability of two criteria in differentiating these two forms: the mean beta-cell nuclear radius (MNR) and the beta-cell nuclear crowding, i.e. the number of nuclei per 1000 micron 2 beta-cell (BCNC). The values of the largest MNR and of BCNC in cases bearing a focal lesion (respectively, 3.27 microns +/- 0.25 and 14.62 +/- 1.78) were significantly different from those in the diffuse pathology (4.25 microns +/- 0.43 and 10.00 +/- 1.55). Setting the threshold value of MNR at 3.70 microns and that of BCNC at 12.00 enabled correct classification of 90.9% of the diffuse and 100% of the focal forms. beta-Cell nuclear analysis can thus contribute to a subclassification of the syndrome, not allowed by clinical or biological data. If performed during surgery it could help in determining the extent of pancreatectomy necessary to cure the patient, as the diffuse form, with abnormal nuclei in the whole pancreas, requires subtotal to near-total pancreatectomy, whereas the focal form, devoid of abnormal insular beta-cell nuclei, can be cured by partial pancreatectomy.

Somatic deletion of the imprinted 11p15 region in sporadic persistent hyperinsulinemic hypoglycemia of infancy is specific of focal adenomatous hyperplasia and endorses partial pancreatectomy

Sporadic persistent hyperinsulinemic hypoglycemia of infancy (PHHI) or nesidioblastosis is a heterogeneous disorder characterized by profound hypoglycemia due to inappropriate hypersecretion of insulin. An important diagnostic goal is to distinguish patients with a focal hyperplasia of islet cells of the pancreas (FoPHHI) from those with a diffuse abnormality of islets (DiPHHI) because management strategies differ significantly. 16 infants with sporadic PHHI resistant to diazoxide and who underwent pancreatectomy were investigated. Selective pancreatic venous sampling coupled with peroperative surgical examination and analysis of extemporaneous frozen sections allowed us to identify 10 cases with FoPHHI and 6 cases with DiPHHI. We show here that in cases of FoPHHI, but not those of DiPHHI, there was specific loss of maternal alleles of the imprinted chromosome region 11p15 in cells of the hyperplastic area of the pancreas but not in normal pancreatic cells. This somatic event is consistent with a proliferative monoclonal lesion. It involves disruption of the balance between monoallelic expression of several maternally and paternally expressed genes. Thus, we provide the first molecular explanation of the heterogeneity of sporadic forms of PHHI such that it is possible to perform only partial pancreatectomy, limited to the focal somatic lesion, so as to avoid iatrogenic diabetes in patients with focal adenomatous hyperplasia.

Endothelin-3 gene mutations in isolated and syndromic Hirschsprung disease

Hirschsprung disease (HSCR, aganglionic megacolon) is a frequent congenital malformation regarded as a multigenic neurocristopathy. Four susceptibility genes have recently been identified in HSCR, namely the RET proto-oncogene, the glial cell line-derived neurotrophic factor (GDNF), the endothelin B receptor (EDNRB) and the endothelin-3 genes (EDN3). Homozygosity for EDN3 mutations has been previously shown to cause the Shah-Waardenburg syndrome, a combination of HSCR with features of the Waardenburg syndrome. Here, we report on heterozygous EDN3 missense mutations in isolatec HSCR. The present data give further support to the role of the endothelin signaling pathway in the development of neural crest-derived enteric neurons. They also suggest the possibility that either recessive or weakly penetrant dominant alleles could occur at the EDN3 locus, depending on the nature of the mutation.

[Familial adenomatous polyposis and thyroid cancer]

Familial adenomatous polyposis may exhibit extracolonic tumors which include thyroid carcinoma. It has been recently suggested that thyroid carcinomas associated with familial adenomatous polyposis show distinct histologic features different from sporadic follicular or papillary thyroid carcinomas. We report a case of thyroid carcinoma in a young girl affected by familial adenomatous polyposis, whose thyroid tumor exhibited some of these features. This finding confirms the peculiar histologic phenotype of the thyroid carcinomas associated with familial adenomatous polyposis. Alterations of the APC gene responsible for familial adenomatous polyposis may play a role in the development of these thyroid cancers.

Germline mutations of the RET ligand GDNF are not sufficient to cause Hirschsprung disease

Hirschsprung disease (HSCR, aganglionic megacolon) is a common congenital malformation leading to bowel obstruction, with an incidence of 1/5,000 live births. It is characterized by the absence of intrinsic ganglion cells in the myenteric and submucosal plexuses along variable lengths of the gastrointestinal tract. As enteric neurons are derived from the vagal neural crest, HSCR is regarded as a neurocristopathy. On the basis of a skewed sex-ratio (M/F = 4/1) and a risk to relatives much higher than the incidence in the general population, HSCR has long been regarded as a sex-modified multifactorial disorder. Accordingly, segregation analysis suggested an incompletely penetrant dominant inheritance in HSCR families with aganglionosis extending beyond the sigmoid colon. We and others have mapped a dominant gene for HSCR to chromosome 10q11.2 and have ascribed the disease to mutations in the RET proto-oncogene. However, the lack of genotype-phenotype correlation, the low penetrance and the sex-dependent effect of RET mutations supported the existence of one or more modifier gene(s) in familial HSCR. In addition, thus far, RET mutations only accounted for 50% and 15-20% of familial and sporadic HSCR patients, respectively. RET encodes a tyrosine kinase receptor whose ligand was unknown. Recently, the Glial cell line-derived neurotrophic factor (GDNF) has been identified to be a ligand for RET. Moreover, Gdnf-/- knockout mutant mice display congenital intestinal aganglionosis and renal agenesis, a phenotype very similar to the Ret-/- mouse. These data prompted us to hypothesize that mutations of the gene encoding GDNF could either cause or modulate the HSCR phenotype in some cases.

Serial transabdominal amnioinfusion in the management of gastroschisis with severe oligohydramnios

Two fetuses with gastroschisis diagnosed in utero (at 19 weeks' gestation) had severe oligohydramnios at 30 to 31 weeks. Serial transabdominal amnioinfusions were performed to fill the amniotic cavity with saline, thereby avoiding the potential consequences of fetal exposure to severe oligohydramnios. In both cases, premature rupture of membranes occurred at 36 weeks, and the fetuses were delivered by cesarean section. There were minimal lesions of the extraabdominal bowel. After primary closure of the abdomen, the postoperative course was uneventful. These observations show that serial amnioinfusion is a feasible therapeutic approach for severe third-trimester oligohydramnios associated with gastroschisis.

Testicular dysgenesis does not affect expression of anti-müllerian hormone by Sertoli cells in premeiotic seminiferous tubules

Anti-Müllerian hormone (AMH) immunoreactivity was studied on paraffin sections obtained from archival testicular biopsies of 29 children with intersex disorders and of 22 controls. Strong AMH immunoreactivity was observed in Sertoli cell cytoplasm from 8 fetal weeks until puberty. During pubertal maturation, in both normal and intersex patients, AMH expression was present in premeiotic seminiferous tubules, but was no longer detected in neighboring tubules with meiotic development. AMH immunostaining was abolished in the testis of one patient with persistent Müllerian ducts due to a mutation of the AMH gene, but was conserved in the testes of two patients with mutations of the AMH receptor gene. Testicular dysgenesis usually results in sexual ambiguity, with low testosterone and AMH serum levels and persistence of Müllerian derivatives. AMH immunoreactivity was conserved in premeiotic seminiferous tubules of dysgenetic testes, and also in sex-cord cells of a gonadoblastoma. In patients with asymmetric gonadal differentiation, the streak gonad was AMH-negative. In conclusion, secretion of AMH is a constitutive feature of the immature Sertoli cell and its expression is altered only by mutations of the AMH gene, but not by gonadal dysgenesis. The degree of regression of Müllerian ducts and serum AMH levels reflect the number, not the functional value, of Sertoli cells present in the immature testis.

Heterozygous endothelin receptor B (EDNRB) mutations in isolated Hirschsprung disease

Hirschsprung disease (HSCR, aganglionic megacolon) is a frequent congenital malformation regarded as a multigenic neurocristopathy. Two susceptibility genes have been recently identified in HSCR, namely the RET proto-oncogene and the endothelin B receptor (EDNRB) gene. Hitherto however, homozygosity for EDNRB mutations accounted for the HSCR-Waardenburg syndrome (WS) association. Here, we report heterozygous EDNRB missense mutations (G57S, R319W and P383L) in isolated HSCR. These data might suggest that EDNRB mutations could be dosage sensitive: heterozygosity would predispose to isolated HSCR with incomplete penetrance, while homozygosity would result in more complex neurocristopathies associating HSCR and WS features. In addition, the present data give further support to the role of the endothelin-signalling pathway in the development of neural crest-derived enteric neurons.

[Genetics of Hirschsprung disease]

Hirschsprung's disease (HD) is one of the commonest gastrointestinal malformations, as it affects one child out of 5,000 births. It classically induces severe neonatal intestinal obstruction requiring surgical treatment which currently ensures a favourable prognosis for most of the affected children. Although the great majority of cases are sporadic, the existence of familial forms (10% of cases) has allowed localization and then identification of an autosomal dominant gene on chromosome 10, the RET proto-oncogene, responsible for 50% of familial forms and 15% of sporadic cases. A second gene has been recently localized on chromosome 13, the endothelium beta receptor (EDNRB) gene. Two homozygous mutations of the EDNRB gene have been identified in two consanguineous families, in which HD is associated with Waardenburg's syndrome (WS). Other heterozygous mutations have been identified in patients presenting with isolated HD and an 5% of cases of HD can be considered to present mutations of this gene. Finally, the authors have recently identified a mutation of the endothelium gene 3 (EDN3), one of the EDNRB ligands in a patient presenting with a combination of HD and WS. This mutation, present at the homozygous state in this patient, is predictive of complete absence of EDN3 protein: this is therefore the third known gene responsible for HD.

[Genetics of Hirschsprung disease]

Hirschsprung disease (HD) is one of the commonest gastro-intestinal malformations, as it affects one child out of 5,000 births. It classically induces severe neonatal intestinal obstruction requiring surgical treatment which currently ensures a favourable prognosis for most of the affected children. Although the great majority of cases are sporadic, the existence of familial forms (10% of cases) has allowed the localization and then the identification of an autosomal dominant gene on chromosome 10, the RET proto-oncogene, responsible for 50% of familial forms and 15% of sporadic cases. A second gene has been recently localized on chromosome 13, the endothelin beta receptor (EDNRB) gene. Two homozygous mutations have been identified in two consanguineous families, in which HD is associated with Waardenburg syndrome (WS). Other heterozygous mutations have been identified in patients presenting with isolated HD and 5% of cases can be considered to present mutations of this gene. Finally the authors have recently identified a mutation of the endothelin 3 gene (EDN3), one of EDNRB ligands in a patient presenting a combination of HD and WS. This mutation, present at the homozygous state in this patient, is predictive of complete absence of EDN3 protein: this is therefore the third known gene responsible for HD.

Diversity of RET proto-oncogene mutations in familial and sporadic Hirschsprung disease

Hirschsprung disease (HSCR) is a common congenital malformation (1 in 5,000 live births) due to the absence of autonomic ganglia in the terminal hindgut, and resulting in intestinal obstruction in neonates. Recently, a dominant gene for familial HSCR has been mapped to chromosome sub-band 10q11.2 and the disease has been ascribed to mutations in a tyrosine kinase receptor gene mapping to this region, the RET proto-oncogene. Studying the 20 exons of the RET gene by a combination of denaturating gradient gel electrophoresis and single strand conformation polymorphism in a large series of HSCR patients (45 sporadic cases and 35 familial forms), we found mutations of the RET gene in 50% of familial HSCR, regardless of the length of the aganglionic segment. The mean penetrance of the mutant allele in familial HSCR was significantly higher in males (72%) than in females (51%). Most interestingly, mutations at the RET locus accounted for at least 1/3 of sporadic HSCR in our series. These mutations were scattered along the length of the gene. Finally, among the mutations identified in sporadic cases (16/45), seven proved to be de novo mutations suggesting that new mutations at the RET locus significantly contribute to sporadic HSCR. Taken together, the low penetrance of the mutant gene, the lack of genotype-phenotype correlation, the sex-dependent effect of RET mutations and the variable clinical expression of the disease support the existence of one or more modifier genes in familial HSCR.

[Conjoined omphalopagous twins separated at fifteen days of age]

BACKGROUND

Conjoined (siamese) twins represent a rare situation which may occur in 1 of every 50,000 births. A prenatal diagnosis usually leads to stopping pregnancy. We report a case with successful surgical separation at the age of 15 days.

CASE REPORT

Ultrasonographic examination at 20 weeks of gestation showed omphalopagus siamese joined at the abdomen from the xiphoid process to the umbilicus. Conjoined structures included liver. There was a multicystic right kidney in one twin, without other malformation. Karyotype was normal, 46XX. The mother refused interruption of her pregnancy. Both girls were born by cesarean section. Angiography, magnetic resonance imaging and intravenous urography confirmed the ultrasound examination. There was no cross circulation into the liver and the gastrointestinal tract was not conjoined. The twins were separated at 15 days of age with right heminephrectomy of the multicystic kidney. The girls are now 16 months old and are in very good health.

CONCLUSION

Prognosis of siamese twins depends on the nature of joined structures and presence of malformations. Ultrasonographic examination during pregnancy shows the possibility of surgical separation, which is performed by a double anesthetic and surgical pediatric team. Preoperative investigations must include MRI.

True hermaphroditism: genetic variants and clinical management

The diagnosis and management of 22 patients with true hermaphroditism are described. Sixteen of them were first seen before the age of 4 months. The initial manifestations were ambiguous genitalia in 20 cases (two of them identified prenatally by ultrasound examination), isolated clitoromegaly in one, and penile hypospadias plus unilateral cryptorchidism in one. All patients but one had at least one palpable gonad. Eleven of the twelve patients examined before the age of 6 months had basal plasma testosterone levels > 0.4 ng/ml. In older patients the stimulation test was necessary to demonstrate male testosterone secretion. The most common peripheral karyotype was 46,XX (17 cases); the other karyotypes were 47,XXY (1 case) and mosaicism 46,XX/46,XY (2 cases) or 46,XX/47,XXY (2 cases). One of the patients with the 46,XX karyotype had 46,XX/46,XY on fibroblast culture; four had the SRY gene in their leukocytes and one in the tissue taken at gonadal biopsy. A vagina was found in all patients at laparotomy, and a uterus was found in 17 cases (as a hemiuterus in 9). Genitography failed to demonstrate a uterus in only one case. The testicular tissue was dysgenetic but the ovarian tissue was normal. Sex assignment was male in 8 patients (reoriented by us in 2) and female in 14 patients (reoriented by us in 3). Spontaneous pubertal development occurred in the 4 patients (2 boys, 2 girls) with gonadal tissue who reached pubertal age. We conclude that true hermaphroditism is a heterogeneous condition in terms of its genetic background, with a prevalence of the 46,XX karyotype. There may be mosaicism with a Y-bearing cell line limited to the gonad (its frequency is probably underestimated), a paternal meiotic exchange between X and Y occurring in 46,XX cases with SRY, or a lack of the SRY gene, suggesting that other genes working independently of SRY may also determine testicular differentiation.

Mutations of the RET proto-oncogene in Hirschsprung's disease

Hirschsprung's disease (HSCR) is a common condition (1 in 5,000 live births) resulting in intestinal obstruction in neonates and megacolon in infants and adults. This disease has been ascribed to the absence of autonomic ganglion cells, which are derived from the neural crest, in the terminal hindgut. Segregation analyses have suggested incompletely penetrant dominant inheritance in familial HSCR. Recently, a gene for HSCR has been mapped to chromosome 10q11.2 (refs 6, 7). No recombination was observed between the disease locus and the locus for the RET proto-oncogene, a protein tyrosine kinase gene expressed in the cells derived from the neural crest. Here we report nonsense and missense mutations in the extracellular domain of RET protein (exons 2, 3, 5 and 6) in six unrelated probands and show that the mutant genotypes segregate with the disease in HSCR families. Mutations of RET have been previously reported in multiple endocrine neoplasia type 2A (MEN 2A). Thus, germ-line mutations of the RET gene may contribute either to developmental anomalies in HSCR or to inherited predisposition to cancer in MEN 2A.