Holoprosencephaly and polydactyly: a possible expression of the hydrolethalus syndrome

Modeling Rare Human Disorders in Mice: The Finnish Disease Heritage

The modification of genes in animal models has evidently and comprehensively improved our knowledge on proteins and signaling pathways in human physiology and pathology. In this review, we discuss almost 40 monogenic rare diseases that are enriched in the Finnish population and defined as the Finnish disease heritage (FDH). We will highlight how gene-modified mouse models have greatly facilitated the understanding of the pathological manifestations of these diseases and how some of the diseases still lack proper models. We urge the establishment of subsequent international consortiums to cooperatively plan and carry out future human disease modeling strategies. Detailed information on disease mechanisms brings along broader understanding of the molecular pathways they act along both parallel and transverse to the proteins affected in rare diseases, therefore also aiding understanding of common disease pathologies.

Syndromes associated with holoprosencephaly

Holoprosencephaly (HPE) is partial or complete failure of the forebrain to divide into hemispheres and can be an isolated finding or associated with a syndrome. Most cases of HPE are associated with a syndrome and roughly 40%-60% of fetuses with HPE have trisomy 13 which is the most common etiology of HPE. Other syndromes associated with HPE include additional aneuploidies like trisomy 18 and single gene disorders such as Smith-Lemli-Opitz syndrome. There are a number of syndromes such as pseudotrisomy 13 which do not have a known molecular etiology; therefore, this review has two parts: syndromes with a molecular diagnosis and syndromes where the etiology is yet to be found. As most HPE is syndromic, this review provides a comprehensive list and description of syndromes associated with HPE that may be used as a differential diagnosis and starting point for evaluating individuals with HPE.

Holoprosencephaly-polydactyly (pseudotrisomy 13) syndrome: case report and diagnostic criteria

We report a new case of a fetus with holoprosencephaly-polydactyly syndrome, also known as pseudo-trisomy 13 syndrome, and no other apparent abnormalities except for septal agenesis of the left lung. The fetal karyotype was normal. Mutational analysis of five genes (SHH, SIX3, TGIF, ZIC2, and GLI3), which are major genes associated with holoprosencephaly, did not disclose any mutational findings. We therefore propose that the abnormalities of our fetus support the demarcation of this syndrome as an autonomous phenotype. Specific diagnostic criteria for holoprosencephaly-polydactyly syndrome need to be complemented by the absence of mutations in the major holoprosencephaly genes.

Hydrocephalus with cleft lip and palate: an overlap between midline malformation syndromes

We present a male infant with hydrocephalus, cleft lip/palate, micrognathia, club foot, laryngeal stenosis and ostium secundum type atrial septal defect. The karyotype was 46 XY. The combination of malformations observed overlaps with the characteristic findings of hydrolethalus syndrome, Meckel syndrome, Smith-Lemli-Opitz syndrome and pseudotrisomy 13. We discussed the differential diagnosis of the case.

Cortical thinning and hydrocephalus in mice lacking the immunoglobulin superfamily member CDO

CDO is a cell surface immunoglobulin superfamily member that positively regulates myogenic differentiation in vitro and in vivo and signals to posttranslationally activate myogenic basic helix-loop-helix (bHLH) transcription factors. The Cdo gene is also expressed in the dorsal aspect and midline structures of the developing central nervous system, and mice lacking CDO on the C57BL/6 background display holoprosencephaly with approximately 80% penetrance, resulting in perinatal lethality. We report here that a fraction of Cdo-/- mice from this background have additional defects in brain development, including hydrocephalus and cortical thinning. Primary neural progenitor cultures from E14.5 Cdo-/- mutants display reduced proliferation, which may underlie the thinning. The cortical preplate and cortices of mutant animals also show reduced staining for beta-tubulin III, indicating defective neuronal differentiation. CDO levels are strongly increased in cultured C17.2 neuronal precursor cells stimulated to differentiate; modulation of CDO levels in these cells by overexpression or interfering RNA approaches enhances or diminishes differentiation, respectively. Cotransfection of CDO enhances the activity of the neurogenic bHLH factor, neurogenin1, in reporter assays and enhances heterodimerization of neurogenin1 and E47. These results indicate that CDO promotes neuronal differentiation and support the hypothesis that CDO coordinates differentiation of multiple cell lineages by regulating the activity of tissue-specific bHLH factors.

Pseudotrisomy 13 syndrome: a case with left ventricular hypoplasia and duodenal stenosis

We report a case of a female child born at 32 weeks of gestation. Birth weight was 1200 g (<3rd centile), length 40 cm (10th-50th centile) and head circumference 23.5 cm (<3rd centile). Clinical examination revealed microcephaly, hypotelorism, microphthalmia, a flat rudimentary nose with a single nasal cavity, high palate, thick dysplastic low-set ears, a short neck, postaxial polydactyly of the upper limbs, and single palmar creases. Investigations showed alobar holoprosencephaly, absence of the third ventricle and midline structures of the brain, microphthalmia, hypotelorism, left ventricular hypoplasia, a large atrial septal defect, and duodenal stenosis. The karyotype was 46,XX. A hypoplastic left ventricle and duodenal stenosis have not been previously reported in pseudotrisomy 13 and this case might aid in the further delineation of this syndrome.

An Asian girl with a 'milder' form of the Hydrolethalus syndrome

Hydrolethalus syndrome is an autosomal recessive disorder characterized by hydrocephalus, micrognathia, limb anomalies and several other abnormalities, mostly in the midline structures. The syndrome was first described in Finland, where the incidence is approximately 1 in 20000. All of the Finnish patients were stillborn or died during the first day of life. Only three non-Finnish cases have survived beyond the neonatal period. Here, we report the first Oriental girl with a 'milder' form of hydrolethalus syndrome. The patient died at age 44 days making her the fourth reported case surviving beyond the neonatal period. The case supports the concept of a 'milder' form of the syndrome. Whether this spectrum is due to allelism or locus heterogeneity awaits molecular analysis.

Hydrolethalus syndrome in a non-Finnish family: confirmation of the entity and early prenatal diagnosis

We present a family in which the first affected child presented with a 'milder' form of the hydrolethalus syndrome and survived to seven months, and two subsequent pregnancies with typical features detected early by ultrasound evaluation. We propose that the 'milder' cases are indeed true cases of the hydrolethalus syndrome and that allelic variability may be responsible for these 'non-typically Finnish' findings. We also demonstrate that, especially in families where there has been a previously affected fetus, echographic diagnosis can be made in the first trimester, as early as the 11th week of gestation.

Acrocallosal syndrome in an Algerian boy born to consanguineous parents: review of the literature and further delineation of the syndrome

We present a 17-month-old boy with the acrocallosal syndrome. He was born to consanguineous parents. Abnormal findings included agenesis of the corpus callosum, a ventricular septal defect (VSD), postaxial polydactyly of fingers, cleft soft palate, intestinal malrotation, large anterior fontanelle, prominent forehead, hypertelorism, epicanthic folds, short nose and mandible and preauricular skin tags, mixed hearing loss, laryngomalacia, and growth and severe motor and mental retardation. A review of previous reports on the acrocallosal syndrome shows considerable clinical variability; minimal diagnostic criteria are proposed. A developmental field defect with disturbance of midline development is suggested.

Dandy-Walker malformation and polydactyly: a possible expression of hydrolethalus syndrome

Hydrolethalus syndrome consists of hydrocephalus, polydactyly, micrognathia, midcranial malformations, visceral abnormalities and perinatal lethality. It was first described in Finland, and only a few other cases outside Scandinavia are known. We report the first Hungarian patient who displayed many signs of the syndrome but had no cleft lip and visceral abnormalities. This observation suggests the existence of oligosymptomic hydrolethalus syndrome, and suggests that Dandy-Walker malformation with polydactyly may be a manifestation of the hydrolethalus syndrome.

Multiple congenital malformations in two sibs reminiscent of hydrolethalus and pseudotrisomy 13 syndromes

We report on two sibs, born to consanguineous parents, with defects of the midline including cleft lip and palate, flat nose, hypotelorism, and dysgenesis of corpus callosum, in addition to short limbs, radiolucent tibial notch, digital anomalies, ambiguous genitalia, and hypopituitarism. In spite of the similarities between this condition and the hydrolethalus and pseudotrisomy 13 syndromes, our patients had neither preaxial nor postaxial polydactyly, but had previously undescribed bilateral radiolucent tibial notch, which is not known to be part of those two syndromes. The cases presented here may very well represent a new autosomal recessive syndrome.

Numerical syndromology: a mathematical approach to the nosology of complex phenotypes

Numerical taxonomy is defined by Sneath and Sokal as the grouping of taxonomic units on the basis of their character states by numerical methods of multivariate data analysis, and syndromology as the study of multiple congenital anomaly (MCA) syndromes and of their nosology. We present here an application of those methods to the analysis of overlapping syndromes. The main advantage of numerical taxonomy is that it allows simultaneous objective and unweighted analysis of multiple traits, giving the possibility to test mathematically the clinical hypotheses about the heterogeneity between closely resembling syndromes and uncovering objective patterns of anomalies, to be compared with the subjective pattern recognition process which characterizes most of the diagnostic approach in syndromology. In this paper, we explored 5 syndromes whose most severe expression belongs to the cerebroacrovisceral early lethality (CAVE) phenotype: hydrolethalus, severe Smith-Lemli-Opitz, orofaciodigital type VI (Varadi-Papp), holoprosencephaly-polydactyly, and Pallister-Hall syndromes. Fifty-five published cases, including many overlapping cases, were submitted to principal factor analysis followed by hierarchical clustering and graphical scaling. Results show that the 5 syndromes clearly constitute independent phenotypic entities, that some of the original diagnoses have to be reconsidered, and that many of the overlapping cases may be unambiguously set in one category. Hypothalamic hamartoblastoma appears to be a nonspecific dysplasia occurring in any of the 5 disorders.

Further delineation of pseudotrisomy 13 syndrome: a case without polydactyly

We report on a baby with holoprosencephaly, median cleft lip, cardiac and genital anomalies, normal upper limbs, and a 46,XX karyotype. We also reviewed 22 karyotypically normal cases whose clinical features resembled trisomy 13 syndrome and compared them with the case we present. The problem of variable expression of the pseudotrisomy 13 syndrome versus genetic heterogeneity is illustrated.

Pseudotrisomy 13 and autosomal recessive holoprosencephaly

Two sibs, diagnosed prenatally, had holoprosencephaly, midface hypoplasia, and normal chromosomes. The first fetus also had polydactyly. This sibship may represent an example of autosomal recessive pseudotrisomy 13.

"Holoprosencephaly-polydactyly" (pseudotrisomy 13) syndrome: expansion of the phenotypic spectrum

Analysis of familial cases of the so called "holoprosencephaly-polydactyly" ("pseudotrisomy 13") syndrome shows that neither holoprosencephaly, nor polydactyly are obligatory manifestations of this condition. This review of previous case reports shows that each of these anomalies is only found in approximately 60% of affected sibs, and therefore these sentinel abnormalities are not required for diagnosis. We propose a widening of the phenotypic spectrum of this syndrome and consideration of the use of an eponomic name, such as the Cohen-Gorlin syndrome, or clear recognition that the sentinel findings of holoprosencephaly and polydactyly are not essential for diagnosis. We propose the following diagnostic criteria for the syndrome. The diagnostic criteria for sporadic cases would include a normal karyotype and either (1) a combination of holoprosencephaly and post-axial polydactyly with or without other characteristics, or (2) a combination of holoprosencephaly with other characteristics but without polydactyly, or (3) a combination of postaxial polydactyly, brain defects (microcephaly, hydrocephaly, agenesis of corpus callosum) and other characteristics. The diagnostic criteria for the familial cases would be the same, except that, as long as the other sibs have no abnormalities contradicting the diagnosis, a normal karyotype would be required in only one affected sib.

Two consecutive hydrolethalus syndrome-affected pregnancies in a nonconsanguinous black couple: discussion of problems in prenatal differential diagnosis of midline malformation syndromes

Hydrolethalus syndrome is a rare autosomal recessive (AR) disorder characterized by polyhydramnios, CNS abnormalities, cleft lip/palate, micrognathia, and polydactyly. Its molecular basis is unknown and prenatal diagnosis is challenging due to phenotypic overlap with several other midline malformation syndromes. A 34-year-old G3P2, nonconsanguinous, married, African-American woman was referred at 19 weeks of gestation after ultrasound findings of "multiple congenital anomalies." A previous pregnancy had been terminated following ultrasound findings of polyhydramnios, cleft lip/palate, polydactyly, severe hydrocephalus, and a Dandy-Walker malformation (DWM). Level II ultrasound evaluation of the current pregnancy demonstrated all of the anomalies which had been present in her previous pregnancy. Karyotype of amniocytes was 46,XX. Autopsy following pregnancy termination confirmed ultrasound findings. The pedigree, sonographic, and autopsy findings in this case were most consistent with hydrolethalus syndrome, although other AR multiple midline malformation syndromes were considered. Our case was detected by 19 weeks. Confident differential diagnosis is difficult for the geneticist and even more so for the sonologist given the technical limitations of ultrasound. It is uncertain whether these mendelian midline malformation syndromes represent slightly different phenotypic expressions of a common genetic defect or are manifestations of allelic and or locus heterogeneity. We suggest that for prenatal diagnostic purposes, in the absence of knowledge of the molecular basis of these disorders, the fine distinctions are not crucial as long as their mendelian inheritance is recognized and presence or absence of manifestations which make them severe are ascertained.

On lumping and splitting: a fetus with clinical findings of the oral-facial-digital syndrome type VI, the hydrolethalus syndrome, and the Pallister-Hall syndrome

The three midline malformation complexes, the oral-facial-digital syndrome type VI (OFDS VI) or Váradi syndrome, the hydrolethalus syndrome (HS), and the Pallister-Hall syndrome (PHS) have been described as distinct genetic entities. Here, we report a fetus with a combination of clinical findings of all 3 syndromes similar to the twin fetuses described in the accompanying paper (Hingorani et al., 1991). The phenotypic overlap in these fetuses with the OFDS VI, HS, and PHS raises the question as to whether or not they indeed represent separate genetic entities as previously assumed.

Familial holoprosencephaly, heart defects, and polydactyly

We describe a pair of sibs with microcephaly, hypoplastic nose, cleft lip/palate, a complicated Fallot-like cardiac defect, and holoprosencephaly and polydactyly. One sib appeared to have normal chromosomes. The healthy parents were second cousins. This constellation of signs has been described before in at least 14 other patients, and was possibly present in several others. Although there is overlap with a number of similar conditions, especially hydrolethalus syndrome, this probably represents a separate entity. Three pairs of sibs and consanguinity in 3 families point to autosomal recessive pattern of inheritance.

Pseudo-trisomy 13 syndrome

We have coined the term "pseudo-trisomy 13 syndrome" to designate cases of holoprosencephaly, severe facial anomalies, postaxial polydactyly, various other congenital defects, and normal chromosomes. Eleven instances are summarized. Two pairs of sibs and two other cases with consanguinity suggest autosomal recessive inheritance. Autosomal recessive inheritance is possible. Alternately, an undetected microdeletion and etiologic heterogeneity (some cases possibly representing dominant new mutations) must be considered. Further delineation is necessary. It is hoped that this paper will serve as a focus for further discussion of the problem.

Holoprosencephaly-polydactyly ('pseudotrisomy 13') syndrome: a syndrome with features of hydrolethalus and Smith-Lemli-Opitz syndromes. A collaborative multicentre study

A syndrome of holoprosencephaly and postaxial polydactyly, associated with hydrocephalus, heart defect, adrenal hypoplasia, and other visceral malformations, has been observed in five unrelated children with normal chromosomes. Clinical overlap with lethal acrodysgenital dwarfism (Smith-Lemli-Opitz syndrome type II) and hydrolethalus syndrome is discussed. Recessive inheritance seems likely.