Margherita Lerone

Frequency of Ret mutations in long- and short-segment Hirschsprung disease

Hirschsprung disease, or congenital aganglionic megacolon, is a genetic disorder of neural crest development affecting 1:5,000 newborns. Mutations in the RET proto‐oncogene, repeatedly identified in the heterozygous state in both long‐ and short‐segment Hirschsprung patients, lead to loss of both transforming and differentiating capacities of the activated RET through a dominant negative effect when expressed in appropriate cellular systems. The approach of single‐strand conformational polymorphism analysis established for all the 20 exons of the RET proto‐oncogene, and previously used to screen for point mutations in Hirschsprung patients allowed us to identify seven additional mutations among 39 sporadic and familial cases of Hirschsprung disease (detection rate 18%). This relatively low efficiency in detecting mutations of RET in Hirschsprung patients cannot be accounted by the hypothesis of genetic heterogeneity, which is not supported by the results of linkage analysis in the pedigrees analyzed so far. Almost 74% of the point mutations in our series, as well as in other patient series, were identified among long segment patients, who represented only 25% of our patient population. The finding of a C620R substitution in a patient affected with total colonic aganglionosis confirms the involvement of this mutation in the pathogenesis of different phenotypes (i.e., medullary thyroid carcinoma and Hirschsprung). Finally the R313Q mutation identified for the first time in homozygosity in a child born of consanguineous parents is associated with the most severe Hirschsprung phenotype (total colonic aganglionosis with small bowel involvement). Hum Mutat 9:243–249, 1997.

Ectodermal dysplasias: not only ‘skin’ deep

The ectodermal dysplasias (EDs) are a large and complex nosologic group of diseases; more than 170 different pathologic clinical conditions have been identified. Despite the great number of EDs described so far, few causative genes have been identified. We review EDs in the light of the most recent molecular findings and propose a new classification of EDs integrating both molecular‐genetic data and corresponding clinical findings of related diseases.

Genetic Mapping to 10q23.3-q24.2, in a Large Italian Pedigree, of a New Syndrome Showing Bilateral Cataracts, Gastroesophageal Reflux, and Spastic Paraparesis with Amyotrophy

We have recently observed a large pedigree with a new rare autosomal dominant spastic paraparesis. In three subsequent generations, 13 affected individuals presented with bilateral cataracts, gastroesophageal reflux with persistent vomiting, and spastic paraparesis with amyotrophy. Bilateral cataracts occurred in all affected individuals, with the exception of one patient who presented with a chorioretinal dystrophy, whereas clinical signs of spastic paraparesis showed a variable expressivity. Using a genomewide mapping approach, we mapped the disorder to the long arm of chromosome 10 on band q23.3-q24.2, in a 12-cM chromosomal region where additional neurologic disorders have been localized. The spectrum of phenotypic manifestations in this family is reminiscent of a smaller pedigree, reported recently, confirming the possibility of a new syndrome. Finally, the anticipation of symptoms suggests that an unstable trinucleotide repeat may be responsible for the condition.

Heterogeneity and low detection rate of RET mutations in Hirschsprung disease.

Mutations in some exons of the RET proto-oncogene were recently observed in Hirschsprung patients. Using DNA polymorphisms and single-strand conformation polymorphism analysis for the whole coding sequence of the RET proto-oncogene, 82 unrelated Hirschsprung patients were screened systematically. A total of 4 complete deletions of RET and 12 point mutations were identified, each present in no more than one patient and distributed along the whole gene. De novo mutations could be documented in 4 patients. Southern blot and fluorescence in situ hybridization analysis carried out in a restricted number of patients did not reveal any deletion of RET. The low efficiency in detecting mutations of RET in Hirschsprung patients (20%) may originate mainly from genetic heterogeneity.

Single nucleotide polymorphic alleles in the 5′ region of the RET proto-oncogene define a risk haplotype in Hirschsprung’s disease

Hirschsprung’s disease is a congenital disorder characterised by intestinal obstruction caused by the absence of parasympathetic intrinsic ganglion cells along variable lengths of the colon.1 The high proportion of sporadic cases (80–90%), the variable expressivity, the incomplete sex dependent penetrance, and the involvement of several genes, most of which are yet to be identified, show a complex pattern of inheritance for this disorder.2–4 The RET proto-oncogene is the major gene involved in Hirschsprung’s disease, accounting for a high proportion of both familial (about 50%) and sporadic cases (10–15%). Five to ten per cent of patients show alterations in other genes such as the glial cell line derived neurotrophic factor ( GDNF ), neurturin ( NTN ), endothelin 3 ( EDN3 ), endothelin B receptor ( EDNRB ), endothelin converting enzyme 1 ( ECE1 ), transcriptional factor SOX10 , and Smad interacting protein 1 ( SIP1 ).1,5 The small number of affected patients with known mutations confirms the involvement of modifier genes or additional genetic risk factors, some of which are already mapped,3,4,6 in the aetiology of the disease. According to what was expected for a complex inheritance pattern, several common polymorphisms of the RET proto-oncogene have been associated with a variable risk of developing Hirschsprung’s disease. Moreover, specific RET haplotypes have been found to have either protective or predisposing effects, or to modulate the severity of the resulting phenotype.6–12 In particular, specific haplotypes comprising the rarer allele of a single nucleotide polymorphism (SNP) of exon 2 (A45A) have been strongly associated with Hirschsprung’s disease, whereas the haplotype including the rarer allele of exon 14 SNP (S836S) has shown a low penetrant protective effect against the disease.11,12 Recently, Borrego et al have extended the genetic analysis of the SNP2 associated predisposing haplotype for Hirschsprung’s disease, hypothesising the existence of a …

Poland syndrome with bilateral features: Case description with review of the literature†

Poland syndrome (PS) has been described as unilateral pectoral muscle deficiency variably associated with ipsilateral thoracic and upper limb anomalies. Bilateral hypoplasia/aplasia of the pectoralis muscle and upper limb defects in association with variable thoracic muscles, chest wall deformities and lower limb defects have been infrequently reported in the literature. We report on a 3½‐year‐old girl with clinical features consisting in bilateral asymmetric pectoral muscle defects (complete agenesis on the left side and agenesis of the sternocostal head on the right side), nipple hypoplasia, left rib defect, and right hand symbrachydactyly. In this study, we reviewed the bilateral features present in our patient and those described in the literature. Hypotheses explaining bilateral features in PS are reviewed.

Severe end of Opitz trigonocephaly (C) syndrome or new syndrome

We report on four unrelated cases of an Opitz trigonocephaly (C)-like syndrome with a highly characteristic combination of facial anomalies including prominent metopic suture, exophthalmos, hypertelorism, cleft lip and palate, flexion deformities of the upper limbs and multiple other anomalies. We also review two very similar published cases formerly considered to have the C syndrome. Although there is overlap, a clinical distinction from the Opitz trigonocephaly and other syndromes seems possible, and thus a specific causal entity may be postulated.

Ectodermal abnormalities in Kabuki syndrome.

We describe a girl with Niikawa-Kuroki (Kabuki) syndrome (NKS) with conical incisors, hypodontia, hypoplastic nails, and brittle hair. Abnormal teeth are common in NKS and support a hypothesis of autosomal dominant inheritance of the syndrome [Halal et al., 1989; Silengo et al., 1996]. Hair abnormalities have never been investigated in NKS. The ectodermal involvement in NKS could represent an important clue for the understanding of the pathogenesis of this syndrome.

ICF syndrome with variable expression in sibs.

We describe a new familial case of ICF syndrome (immunodeficiency, centromeric instability, facial anomalies) in a woman of 29 years and in her brother of 30 years. The proband showed mental retardation, facial anomalies, recurrent respiratory infections, combined deficit of IgM and IgE immunoglobulin classes, and paracentromeric heterochromatin instability of chromosomes 1, 9, and 16. The brother had minor signs of the syndrome and had an apparently normal phenotype. Their parents were healthy and non-consanguineous. Chromosome anomalies consisted of homologous and non-homologous associations, chromatid and isochromatid breaks, deletions of whole arms, interchanges in the paracentromeric region, and multibranched configurations of chromosomes 1, 9, and 16. CD bands and fluorescence in situ hybridisation with alphoid DNA sequence probes specific for the centromeres of chromosomes 1 and 16 showed that the centromere was not directly implicated in the formation of multibranched configurations. These cases indicate the autosomal recessive mode of inheritance and the variable expressivity of the ICF syndrome.

Microarray based analysis of an inherited terminal 3p26.3 deletion, containing only the CHL1 gene, from a normal father to his two affected children

Backgroundterminal deletions of the distal portion of the short arm of chromosome 3 cause a rare contiguous gene disorder characterized by growth retardation, developmental delay, mental retardation, dysmorphisms, microcephaly and ptosis. The phenotype of individuals with deletions varies from normal to severe. It was suggested that a 1,5 Mb minimal terminal deletion including the two genes CRBN and CNTN4 is sufficient to cause the syndrome.In addition the CHL1 gene, mapping at 3p26.3 distally to CRBN and CNTN4, was proposed as candidate gene for a non specific mental retardation because of its high level of expression in the brain.Methods and Resultswe describe two affected siblings in which array-CGH analysis disclosed an identical discontinuous terminal 3p26.3 deletion spanning less than 1 Mb. The deletion was transmitted from their normal father and included only the CHL1 gene. The two brothers present microcephaly, light mental retardation, learning and language difficulties but not the typical phenotype manifestations described in 3p- syndrome.Conclusiona terminal 3p26.3 deletion including only the CHL1 gene is a very rare finding previously reported only in one family. The phenotype of the affected individuals in the two families is very similar and the deletion has been inherited from an apparently normal parent. As already described for others recurrent syndromes with variable phenotype, these findings are challenging in genetic counselling because of an evident variable penetrance.