Stringent delineation of Pallister-Hall syndrome in two long surviving patients: importance of radiological anomalies of the hands

Clinical and molecular heterogeneity of syndromic hypothalamic hamartoma

Two children are presented who have a distinct syndrome of multiple buccolingual frenula, a stiff and short fifth finger with small nails, a hypothalamic hamartoma, mild to moderate neurological impairment, and mild endocrinological symptoms. No variant assessed to be pathogenic or likely pathogenic was detected in the GLI3 gene in either child. This syndrome appears to be distinct from the inherited Pallister-Hall syndrome associated with GLI3 variants, which is characterized by hypothalamic hamartoma, mesoaxial polydactyly, and other anomalies. In the individuals described here, manifestations outside of the central nervous system were milder and the mesoaxial polydactyly, which is common in individuals with Pallister-Hall syndrome, was absent. Instead, these children had multiple buccolingual frenula together with the unusual appearance of the fifth digit. It remains unclear whether these two individuals represent a separate nosologic entity or if they represent a milder manifestation of one of the more severe syndromes associated with a hypothalamic hamartoma.

A GLI3 variant leading to polydactyly in heterozygotes and Pallister-Hall-like syndrome in a homozygote

Variants in transcriptional activator Gli Kruppel Family Member 3 (GLI3) have been reported to be associated with several phenotypes including Greig cephalopolysyndactyly syndrome (MIM #175700), Pallister-Hall syndrome (PHS) (MIM #146510), postaxial polydactyly types A1 (PAPA1) and B (PAPB) (MIM #174200), and preaxial polydactyly type 4 (MIM #174700). All these disorders follow an autosomal dominant pattern of inheritance. Hypothalamic hamartomas (MIM 241800) is associated with somatic variants in GLI3. We report a related couple with parents having PAPA1 and PAPB, who had a fetus with a phenotype most compatible with PHS. Molecular analyses demonstrated homozygosity for a pathogenic GLI3 variant (c.1927C > T; p. Arg643*) in the fetus and heterozygosity in the parents. The genetic analysis in this family demonstrates that heterozygosity and homozygosity for the same GLI3 variant can cause a different phenotype. Furthermore, the occurrence of Pallister-Hall-like syndrome in a homozygous patient should be taken into account in genetic counseling of families with PAPA1/PAPB.

Pallister-Hall syndrome with orofacial narrowing and tethered cord: a case report

Background

Pallister–Hall syndrome is a rare, autosomal dominant, genetic disorder characterized by different congenital abnormalities: hypothalamic hamartoblastoma, bifid or shortened epiglottis, polydactyly, renal anomalies, and imperforate anus.

Case presentation

In this case report, we describe the case of a 13-year-old Lebanese-Armenian boy born with Pallister–Hall syndrome showing newly associated manifestations (orofacial narrowing and tethered cord), and currently showing a spontaneous puberty with normal growth pattern following management with growth hormones.

Conclusions

This case report shows a practical approach to this very rare syndrome, mainly with testosterone and growth hormones, and its follow-up in the long term. Being familiar with such cases may allow improvement of our knowledge for better management in the future.

GLI3-related polydactyly: a review

GLI3 mutations are known to be associated with nine syndromes/conditions in which polydactyly is a feature. In this review, the embryology, pathogenesis, and animal models of GLI3-related polydactyly are discussed first. This is followed by a detailed review of the genotype-phenotype correlations. Based on our review of the literature and our clinical experiences, we recommend viewing GLI3-related syndromes/conditions as four separate entities; each characterized by a specific pattern of polydactyly. These four entities are: the preaxial polydactyly type IV-Greig-acrocallosal spectrum, postaxial polydactyly types A/B, Pallister-Hall syndrome (PHS), and oral-facial-digital overlap syndrome. We also provide illustrative clinical examples from our practice including a family with a novel GLI3 mutation causing PHS. The review also introduces the term 'Forme Fruste' preaxial polydactyly and gives several conclusions/recommendations including the recommendation to revise the current criteria for the clinical diagnosis of PHS.

Total colonic aganglionosis and imperforate anus in a severely affected infant with Pallister-Hall syndrome

Pallister-Hall syndrome is a complex malformation syndrome characterized by a wide range of anomalies including hypothalamic hamartoma, polydactyly, bifid epiglottis, and genitourinary abnormalities. It is usually caused by truncating frameshift/nonsense and splicing mutations in the middle third of GLI3. The clinical course ranges from mild to lethal in the neonatal period. We present the first patient with Pallister-Hall syndrome reported with total colonic aganglionosis, a rare form of Hirschsprung disease with poor long-term outcome. The patient also had an imperforate anus, which is the third individual with Pallister-Hall syndrome reported with both Hirschsprung disease and an imperforate anus. Molecular testing via amniocentesis showed an apparently de novo novel nonsense mutation c.2641 C>T (p.Gln881*). His overall medical course was difficult and was complicated by respiratory failure and pan-hypopituitarism. Invasive care was ultimately withdrawn, and the patient expired at three months of age. This patient's phenotype was complex with unusual gastrointestinal features ultimately leading to a unfavorable prognosis and outcome, highlighting the range of clinical severity in patients with Pallister-Hall syndrome.

New insights into genotype-phenotype correlation for GLI3 mutations

The phenotypic spectrum of GLI3 mutations includes autosomal dominant Greig cephalopolysyndactyly syndrome (GCPS) and Pallister-Hall syndrome (PHS). PHS was first described as a lethal condition associating hypothalamic hamartoma, postaxial or central polydactyly, anal atresia and bifid epiglottis. Typical GCPS combines polysyndactyly of hands and feet and craniofacial features. Genotype-phenotype correlations have been found both for the location and the nature of GLI3 mutations, highlighting the bifunctional nature of GLI3 during development. Here we report on the molecular and clinical study of 76 cases from 55 families with either a GLI3 mutation (49 GCPS and 21 PHS), or a large deletion encompassing the GLI3 gene (6 GCPS cases). Most of mutations are novel and consistent with the previously reported genotype-phenotype correlation. Our results also show a correlation between the location of the mutation and abnormal corpus callosum observed in some patients with GCPS. Fetal PHS observations emphasize on the possible lethality of GLI3 mutations and extend the phenotypic spectrum of malformations such as agnathia and reductional limbs defects. GLI3 expression studied by in situ hybridization during human development confirms its early expression in target tissues.

Cis-regulatory underpinnings of human GLI3 expression in embryonic craniofacial structures and internal organs

The zinc finger transcription factor Gli3 is an important mediator of Sonic hedgehog (Shh) signaling. During early embryonic development Gli3 participates in patterning and growth of the central nervous system, face, skeleton, limb, tooth and gut. Precise regulation of the temporal and spatial expression of Gli3 is crucial for the proper specification of these structures in mammals and other vertebrates. Previously we reported a set of human intronic cis-regulators controlling almost the entire known repertoire of endogenous Gli3 expression in mouse neural tube and limbs. However, the genetic underpinning of GLI3 expression in other embryonic domains such as craniofacial structures and internal organs remain elusive. Here we demonstrate in a transgenic mice assay the potential of a subset of human/fish conserved non-coding sequences (CNEs) residing within GLI3 intronic intervals to induce reporter gene expression at known regions of endogenous Gli3 transcription in embryonic domains other than central nervous system (CNS) and limbs. Highly specific reporter expression was observed in craniofacial structures, eye, gut, and genitourinary system. Moreover, the comparison of expression patterns directed by these intronic cis-acting regulatory elements in mouse and zebrafish embryos suggests that in accordance with sequence conservation, the target site specificity of a subset of these elements remains preserved among these two lineages. Taken together with our recent investigations, it is proposed here that during vertebrate evolution the Gli3 expression control acquired multiple, independently acting, intronic enhancers for spatiotemporal patterning of CNS, limbs, craniofacial structures and internal organs.

Evidence that FGFR1 loss-of-function mutations may cause variable skeletal malformations in patients with Kallmann syndrome

PURPOSE

Loss-of-function mutations in FGFR1 have been identified in approximately 10% of the Kallmann syndrome (KS) patients. Previous reports have focused mainly on olfactory, reproductive, and some other features such as cleft lip/palate and dental agenesis. Given the ubiquitous expression of FGFR1 during development, other abnormal phenotypes might, however, have been overlooked in these patients. Here, we demonstrate skeletal phenotypic characterization of patients presented with KS and FGFR1 mutations.

MATERIAL AND METHODS

Using the Sanger DNA sequencing technique a cohort of 29 KS patients was screened.

RESULTS

Here, we report on 5 KS patients who carry FGFR1 mutations (Gly270Asp, Gly97Ser, Met161Thr, Ser685Phe and Ala167Ser/Ala167Ser). Three patients presented with skeletal abnormalities, i.e. spine (hemivertebra and butterfly vertebra) and limb (oligodactyly of the feet, fusion of the 4th and 5th metacarpal bones) malformations in two patients and one patient, respectively. The hand phenotype found in the patient cannot be thought of as a counter-type of the hand phenotype resulting from FGFR1 gain-of-function mutations. The skeletal anomalies identified in the 3 KS patients are close to those observed in Fgfr1 conditional knockout mice.

CONCLUSIONS

This study demonstrates that FGFR1 loss-of-function mutations can be associated with skeletal abnormalities also in humans. Further investigations in KS patients who carry FGFR1 mutations are needed to evaluate the prevalence of skeletal defects in this genetic form of KS. Conversely, the presence of bone malformations in a KS patient should direct the geneticist towards a search for mutations in FGFR1.

Genital abnormalities in Pallister-Hall syndrome: Report of two patients and review of the literature

We describe two patients with Pallister-Hall syndrome (PHS) with genital abnormalities: a female with hydrometrocolpos secondary to vaginal atresia and a male with micropenis, hypoplastic scrotum, and bilateral cryptorchidism. Nonsense mutations in GLI3 were identified in both patients. Clinical and molecular findings of 12 previously reported patients who had GLI3 mutations and genital abnormalities were reviewed. Genital features in the male patients included hypospadias, micropenis, and bifid or hypoplastic scrotum, whereas all the females had hydrometrocolpos and/or vaginal atresia. No hotspot for GLI3 mutations has been found. The urogenital and anorectal abnormalities associated with PHS might be related to dysregulation of SHH signaling caused by GLI3 mutations rather than hormonal aberrations. We recommend that clinical investigations of genital abnormalities are considered in patients with PHS, even those without hypopituitarism.

Congenital anomalies of the esophagus

Congenital malformations of the esophagus are frequently encountered by pediatric surgeons, especially esophageal atresia with or without tracheo-esophageal fistula. However, the molecular mechanisms underlying the development of these various anomalies are not clear. Here we present a brief overview of the embryologic development of the tracheoesophageal tube, along with some of the genetic controls which, when defective can lead to abnormal separation of this tube.

Genetic and environmental factors in the etiology of esophageal atresia and/or tracheoesophageal fistula: an overview of the current concepts

Esophageal atresia and/or tracheoesophageal fistula (EA/TEF) are severe congenital anomalies. Although recent years have brought significant improvement in clinical treatment, our understanding of the etiology of these defects is lagging. Many genes and genetic pathways have been implicated in the development of EA/TEF, but only a few genes have been shown to be involved in humans, in animals, or in both. Extrapolating data from animal models to humans is not always straightforward. Environmental factors may also carry a risk, but the mechanisms are yet to be elucidated. This review gives an overview of the current state of knowledge about both genetic and environmental risk factors in the etiology of EA/TEF.

Genitourinary malformations as a feature of the Pallister-Hall syndrome

Pallister-Hall and McKusick-Kaufman syndromes are developmental disorders with well defined phenotypes, distinct loci and different patterns of inheritance. The clinical features can overlap and may cause diagnostic difficulty, particularly if complex genitourinary malformations are present. A case is presented with features of both syndromes but in which a GLI3 mutation has been identified. A literature review of similar cases is presented and it is proposed that these cases probably represent the Pallister-Hall syndrome. A detailed abdominal and perineal examination should be considered in all female patients with the Pallister-Hall syndrome, looking for associated genitourinary anomalies. Conversely, all girls with features suggestive of McKusick-Kaufman syndrome require neuroimaging to look for features of the Pallister-Hall syndrome. The correct diagnosis is important so that the patient and the family may receive appropriate management. It also allows provision for an accurate recurrence risk.

Pallister-Hall syndrome: Unreported skeletal features of aGLI3mutation

We describe two patients with Pallister-Hall syndrome (PHS), both with evidence of a generalized skeletal dysplasia as typified by upper and lower acromesomelic limb shortening and the previously unreported fibular hypoplasia, radio-ulnar bowing, and proximal epiphyseal hypoplasia. Genomic DNA was only available for sequencing analysis in patient 2 and the mutation, c.3386_3387delTT was detected in exon 14 of the GL13 gene. It is also possible that the findings in patient 1 represent the phenotypic expression of a novel GLI3 mutation. This report further expands the PHS phenotype and raises the possibility of specific GLI3 mutations resulting in more severe skeletal features. It also suggests that PHS should be included in the differential diagnosis of antenatally ascertained acromesomelic limb shortening and bowing with fibular hypoplasia particularly in the presence of polysyndactyly.

Molecular and clinical analyses of Greig cephalopolysyndactyly and Pallister-Hall syndromes: robust phenotype prediction from the type and position of GLI3 mutations

Mutations in the GLI3 zinc-finger transcription factor gene cause Greig cephalopolysyndactyly syndrome (GCPS) and Pallister-Hall syndrome (PHS), which are variable but distinct clinical entities. We hypothesized that GLI3 mutations that predict a truncated functional repressor protein cause PHS and that functional haploinsufficiency of GLI3 causes GCPS. To test these hypotheses, we screened patients with PHS and GCPS for GLI3 mutations. The patient group consisted of 135 individuals: 89 patients with GCPS and 46 patients with PHS. We detected 47 pathological mutations (among 60 probands); when these were combined with previously published mutations, two genotype-phenotype correlations were evident. First, GCPS was caused by many types of alterations, including translocations, large deletions, exonic deletions and duplications, small in-frame deletions, and missense, frameshift/nonsense, and splicing mutations. In contrast, PHS was caused only by frameshift/nonsense and splicing mutations. Second, among the frameshift/nonsense mutations, there was a clear genotype-phenotype correlation. Mutations in the first third of the gene (from open reading frame [ORF] nucleotides [nt] 1-1997) caused GCPS, and mutations in the second third of the gene (from ORF nt 1998-3481) caused primarily PHS. Surprisingly, there were 12 mutations in patients with GCPS in the 3' third of the gene (after ORF nt 3481), and no patients with PHS had mutations in this region. These results demonstrate a robust correlation of genotype and phenotype for GLI3 mutations and strongly support the hypothesis that these two allelic disorders have distinct modes of pathogenesis.

Hypothalamic Hamartoma

The incidence of hypothalamic hamartomas (HHs) has increased since the introduction of magnetic resonance (MR) imaging. The etiology of this anomaly and the pathogenesis of its peculiar symptoms remain unclear, but recent electrophysiological, neuroimaging, and clinical studies have yielded important data. Categorizing HHs by the degree of hypothalamic involvement has contributed to the accurate prediction of their prognosis and to improved treatment strategies. Rather than undergoing corticectomy, HH patients with medically intractable seizures are now treated with surgery that targets the HH per se, e.g. HH removal, disconnection from the hypothalamus, stereotactic irradiation, and radiofrequency lesioning. Although surgical intervention carries risks, total eradication or disconnection of the lesion leads to cessation or reduction of seizures and improves the cognitive and behavioral status of these patients. Precocious puberty in HH patients is safely controlled by long-acting gonadotropin-releasing hormone agonists. The accumulation of knowledge regarding the pathogenesis of symptoms and the development of safe, effective treatment modalities may lead to earlier intervention in young HH patients and prevent the decline in their cognitive abilities and quality of life. This review of hypothalamic hamartomas presents current classifications, pathophysiologies, and treatment modalities.

Genetics and developmental biology of oesophageal atresia and tracheo-oesophageal fistula: lessons from mice relevant for paediatric surgeons

Oesophageal atresia and tracheo-oesophageal fistula are relatively frequently occurring foregut malformations of which the aetiology and pathogenesis are poorly understood. Recent results of molecular genetic studies, in particular the use of single and compound mutant mice, have yielded a tremendous increase in the understanding of the molecular mechanisms involved in normal and abnormal foregut morphogenesis. In the introduction of this paper, we review the very early stages of normal and abnormal embryology of the foregut derivatives and the separation of the foregut into a ventral respiratory part and a dorsal digestive part. After that, we describe the genes that have been demonstrated to play an important role in these processes.

Bifid epiglottis associated with Joubert's syndrome

This report presents the case of a 2-year-old boy who had a bifid epiglottis associated with Joubert's syndrome. He had episodic tachypnea and apnea, inspiratory stridor, aspiration, and growth and mental retardation. Direct laryngoscopy demonstrated agenesis of the right half of the epiglottis and hypertrophied mucosa over the arytenoid cartilage. After the hypertrophied mucosa was partially vaporized with a CO2 laser, the inspiratory stridor soon improved and the aspiration was alleviated. Brain magnetic resonance imaging showed cerebellar vermian agenesis and enlargement of the fourth ventricle.

Pallister-Hall syndrome: clinical and MR features

A 4-month-old boy with polydactyly and bifid epiglottis was found to have a large sellar and suprasellar mass. When the diagnosis of Pallister-Hall syndrome was made, conservative management was elected. When the patient was 2 years old, the tumor had grown proportionally with the patient, and he was developing appropriately. Although rare, this entity is important to recognize not only for clinical diagnosis but also for appropriate management and genetic counseling.

The phenotypic spectrum of GLI3 morphopathies includes autosomal dominant preaxial polydactyly type-IV and postaxial polydactyly type-A/B; No phenotype prediction from the position of GLI3 mutations

Functional characterization of a gene often requires the discovery of the full spectrum of its associated phenotypes. Mutations in the human GLI3 gene have been identified in Greig cepalopolysyndactyly, Pallister-Hall syndrome (PHS), and postaxial polydactyly type-A (PAP-A). We studied the involvement of GLI3 in additional phenotypes of digital abnormalities in one family (UR003) with preaxial polydactyly type-IV (PPD-IV), three families (UR014, UR015, and UR016) with dominant PAP-A/B (with PPD-A and -B in the same family), and one family with PHS. Linkage analysis showed no recombination with GLI3-linked polymorphisms. Family UR003 had a 1-nt frameshift insertion, resulting in a truncated protein of 1,245 amino acids. A frameshift mutation due to a 1-nt deletion was found in family UR014, resulting in a truncated protein of 1,280 amino acids. Family UR015 had a nonsense mutation, R643X, and family UR016 had a missense mutation, G727R, in a highly conserved amino acid of domain 3. The patient with PHS had a nonsense mutation, E1147X. These results add two phenotypes to the phenotypic spectrum caused by GLI3 mutations: the combined PAP-A/B and PPD-IV. These mutations do not support the suggested association between the mutations in GLI3 and the resulting phenotypes. We propose that all phenotypes associated with GLI3 mutations be called "GLI3 morphopathies," since the phenotypic borders of the resulting syndromes are not well defined and there is no apparent genotype-phenotype correlation.

Bifid epiglottis

Bifid epiglottis is a rare congenital defect that is often associated with other congenital annomalies. The most common defect associated with a bifid epiglottis are anomalies of the hands and/or feet (90%) while the most dangerous and potentially lethal anomaly if not recognized and treated are hypothalamic hamartomas and hypopituitarism (50%). A bifid epiglottis will often result in severe respiratory distress secondary to laxity of the cartilage and chronic aspirations, which may require surgical intervention. We present the case of a 10-week-old child who was sent for evaluation of stridor and aspiration. Office laryngoscopy demonstrated a true bifid epiglottis and further evaluation demonstrated a hypothalamic hamartoma consistent with Pallister-Hall syndrome. Management of our case as well as those previously presented in the literature are reviewed.

Essential function of Gli2 and Gli3 in the formation of lung, trachea and oesophagus

Foregut malformations (oesophageal atresia, tracheo-oesophageal fistula, lung anomalies and congenital stenosis of the oesophagus and trachea) are relatively common anomalies occurring in 1 in 2,000-5,000 live births, although their aetiology is poorly understood. The secreted glycoprotein Sonic hedgehog (Shh) has been suggested to act as an endodermal signal that controls hindgut patterning and lung growth. In mice, three zinc-finger transcription factors, Gli1, Gli2 and Gli3, have been implicated in the transduction of Shh signal. We report here that mutant mice lacking Gli2 function exhibit foregut defects, including stenosis of the oesophagus and trachea, as well as hypoplasia and lobulation defects of the lung. A reduction of 50% in the gene dosage of Gli3 in a Gli2-/- background resulted in oesophageal atresia with tracheo-oesophageal fistula and a severe lung phenotype. Mutant mice lacking both Gli2 and Gli3 function did not form oesophagus, trachea and lung. These results indicate that Gli2 and Gli3 possess specific and overlapping functions in Shh signalling during foregut development, and suggest that mutations in GLI genes may be involved in human foregut malformations.

Evidence for the involvement of the Gli gene family in embryonic mouse lung development

Murine Gli, Gli2, and Gli3 are zinc finger genes related to Drosophila cubitus interuptus, a component of the hedgehog signal transduction pathway. In the embryonic lung, all three Gli genes are strongly expressed at the pseudoglandular stage, in distinct but overlapping domains of the mesoderm. Expression of Gli and Gli3, but not of Gli2, is subsequently downregulated at the canalicular stage, coincident with a decline in the expression of sonic hedgehog (Shh) and the hedgehog receptor gene, patched (Ptc). Overexpression of Shh in the lung results in increased levels of Ptc mRNA. Gli, but not Gli2, is also upregulated, suggesting a differential involvement of the Gli genes in the regulation of Ptc by SHH during lung development. Gli3 is not upregulated by Shh overexpression. However, its importance for lung development is shown by the finding that Gli3XtJ embryos, homozygous for a mutation involving a deletion of the Gli3 gene, have a stereotypic pattern of abnormalities in lung morphogenesis. The pulmonary defects in these embryos, consisting of localized shape changes and size reductions, correlate with normal Gli3 expression. Thus, our data indicate that one of the Gli genes, Gli3, is essential for normal lung development, and that another, Gli, can be placed downstream of Shh signaling in the lung.

Isolation of a full-length human WNT7A gene implicated in limb development and cell transformation, and mapping to chromosome 3p25

The Wnt gene family has a role in development as well as tumourigenesis. One mouse member, Wnt7a, is vital for limb development in vivo and also possesses transforming ability in vitro. This study reports the isolation of a full length of human homologue of mouse Wnt7a gene by library screening. Yeast artificial chromosome-fluorescence in situ hybridisation (YAC-FISH) mapped the WNT7A gene to chromosome 3p25. Human WNT7A had an ORF encoding a deduced protein of 349 aa that exhibited 97% and 92% identity to mouse Wnt7a at the aa and nucleic acid levels, respectively. It possessed the 22 conserved cysteine residues and 3 more at the amino terminus, and a putative poly A tail. This is the fifth human WNT gene in which a complete cDNA sequence had been determined.

GLI3 frameshift mutations cause autosomal dominant Pallister-Hall syndrome

Pallister-Hall syndrome (PHS, M146510) was first described in 1980 in six newborns. It is a pleiotropic disorder of human development that comprises hypothalamic hamartoma, central polydactyly, and other malformations. This disorder is inherited as an autosomal dominant trait and has been mapped to 7p13 (S. Kang et al. Autosomal dominant Pallister-Hall syndrome maps to 7p13. Am. J. Hum. Genet. 59, A81 (1996)), co-localizing the PHS locus and the GLI3 zinc finger transcription factor gene. Large deletions or translocations resulting in haploinsufficiency of the GLI3 gene have been associated with Greig cephalopolysyndactyly syndrome (GCPS; M175700) although no mutations have been identified in GCPS patients with normal karyotypes. Both PHS and GCPS have polysyndactyly, abnormal craniofacial features and are inherited in an autosomal dominant pattern, but they are clinically distinct. The polydactyly of GCPS is commonly preaxial and that of PHS is typically central or postaxial. No reported cases of GCPS have hypothalamic hamartoma and PHS does not cause hypertelorism or broadening of the nasal root or forehead. The co-localization of the loci for PHS and GCPS led us to investigate GLI3 as a candidate gene for PHS. Herein we report two PHS families with frameshift mutations in GLI3 that are 3' of the zinc finger-encoding domains, including one family with a de novo mutation. These data implicate mutations in GLI3 as the cause of autosomal dominant PHS, and suggest that frameshift mutations of the GLI3 transcription factor gene can alter the development of multiple organ systems in vertebrates.

Exclusion of candidate loci and cholesterol biosynthetic abnormalities in familial Pallister-Hall syndrome

Pallister-Hall syndrome (PHS) was originally described in 1980 in six sporadic cases of children with structural anomalies including hypothalamic hamartoma, polydactyly, imperforate anus, and renal and pulmonary anomalies. In 1993, the first familial cases were reported, including affected sibs and vertical transmission. Three of these families are sufficiently large to allow initial evaluation by linkage studies to candidate genes or loci. We have evaluated candidate loci for PHS based on three clinical observations. The first is a patient with PHS-like malformations, including a hypothalamic hamartoma, and an unbalanced translocation involving 7q and 3p. The second is a family with familial PHS where the founder's father had an autosomal dominant hand malformation previously mapped to 17q. The third is the phenotypic overlap of PHS and Smith-Lemli-Opitz syndrome. In this report, we exclude these loci as candidates for linkage to the PHS phenotype on the basis of lod scores of less than-2.0. We conclude that hypothalamic hamartoma is not specific to PHS and that the dominant hand malformation in one of the families was a coincidence. To evaluate the relationship of PHS to Smith-Lemli-Opitz syndrome, we analysed levels of cholesterol and intermediate metabolites of the later stages of cholesterol biosynthesis. There is no evidence of a generalised disorder of cholesterol biosynthesis in patients with familial PHS. On genetic and biochemical grounds, we conclude that PHS and Smith-Lemli-Opitz syndrome are not allelic variants of a single locus.

Pallister-Hall syndrome

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