Clinical Description
GLI3-related Pallister-Hall syndrome (GLI3-PHS) displays a wide range of severity. The literature frequently reflects the assumption that GLI3-PHS is severe and Greig cephalopolysyndactyly syndrome (GCPS) is mild. This assumption is incorrect, as a minority of individuals with GLI3-PHS show multiple severe anomalies and most individuals with GLI3-PHS are mildly affected with polydactyly, asymptomatic bifid epiglottis, and hypothalamic hamartoma. Without careful clinical evaluation, these individuals may be incorrectly diagnosed with postaxial polydactyly type A (PAP-A).
Hypothalamic hamartoma. Hypothalamic hamartoma is a malformation, not a tumor. Hypothalamic hamartomas grow at the rate of – or more slowly than – the surrounding brain tissue. Hypothalamic hamartomas may be large (≤4 cm in greatest dimension); little correlation exists between the size of the hypothalamic hamartoma and presence or severity of symptoms. Individuals with hypothalamic hamartomas may have neurologic symptoms, although most are asymptomatic. Removal of the hypothalamic hamartoma is not indicated and often results in iatrogenic pituitary insufficiency or other complications.
Endocrine manifestations. The endocrine manifestations of a hypothalamic hamartoma range from isolated growth hormone deficiency or isolated precocious puberty to panhypopituitarism, which can be life threatening. Cortisol deficiency can occur in individuals with nonfamilial GLI3-PHS but appears to be rare in those with familial GLI3-PHS.
Neurologic findings. The best-described neurologic complication of hypothalamic hamartoma is gelastic epilepsy, a partial complex seizure manifest by clonic movements of the chest and diaphragm that simulate laughing. Other types of seizures may be caused by hypothalamic hamartoma. Seizures associated with hypothalamic hamartoma in individuals with GLI3-PHS are generally milder and are responsive to treatment, in contrast to individuals with nonsyndromic hypothalamic hamartoma, who often have refractory seizures [Boudreau et al 2005]. No individual with GLI3-PHS has been shown to have visual field loss even with a hypothalamic hamartoma near the optic chiasm.
Polydactyly. Postaxial polydactyly may be more common than mesoaxial polydactyly in individuals with GLI3-PHS. Postaxial polydactyly (PAP) type A is the presence of a well-formed digit on the ulnar or fibular aspect of the limb. PAP type B is the presence of a rudimentary digit or nubbin in the same location. Mesoaxial (i.e., insertional or central) polydactyly is the presence of six or more well-formed digits with a Y-shaped metacarpal or metatarsal.
Note: The nonspecificity of postaxial polydactyly and the high frequency of PAP type B in persons of central African descent require caution in its use as a diagnostic feature.
Epiglottic abnormalities. Bifid epiglottis is nearly always asymptomatic; however, the more severe clefts of the larynx reported in individuals with GLI3-PHS can cause severe airway symptoms. Posterior laryngeal clefts can be fatal.
Psychiatric and neuropsychological findings. Some individuals with GLI3-PHS have behavioral manifestations, including a few with severe intellectual disability and behavioral disturbances [Ng et al 2004]. A larger study of behavioral manifestations of this disorder was inconclusive, reflecting the difficulty of assessing mild behavioral phenotypes in rare disorders [Azzam et al 2005].
Genitourinary anomalies. Renal abnormalities include cystic malformations, small kidneys, and ectopic ureteral implantation; genitourinary anomalies include hydrometrocolpos. The pathogenetic mechanism of the genitourinary anomalies has been delineated [Blake et al 2016].
Other findings include imperforate anus, pulmonary segmentation anomalies including bilateral bilobed lungs, and nonpolydactyly skeletal anomalies including short limbs.
Prognosis for an individual with GLI3-PHS and no known family history of GLI3-PHS is based on the malformations present in the individual. Literature surveys are not useful for the purpose of establishing the prognosis because there is a large degree of inter-individual heterogeneity and publications tend to show bias of ascertainment to more severe involvement. Although GLI3-PHS has been categorized as a member of the CAVE (cerebroacrovisceral early lethality) group of disorders, few affected individuals have an early lethality phenotype. The CAVE descriptor should be discouraged. Early lethality in GLI3-PHS is most likely attributable to panhypopituitarism that is caused by pituitary or hypothalamic dysplasia or severe airway malformations such as laryngotracheal clefts. In addition, imperforate anus can cause serious complications if not recognized promptly. Thus, in the absence of life-threatening malformations, the prognosis should be assumed to be good for individuals with the nonfamilial occurrence of GLI3-PHS. For individuals with a family history of affected family members, the prognosis is based on the degree of severity present in the family.
Mosaicism. Several individuals with nonsyndromic hypothalamic hamartomas and somatic mosaicism for a GLI3 pathogenic variant in the hamartoma have been reported [Wallace et al 2008]. While these individuals do not meet the clinical diagnostic criteria for GLI3-PHS sensu stricto, they may be considered to have a partial form of GLI3-PHS, and consideration should be given to evaluating such individuals for other manifestations of the disorder.
Sub-PHS. A previous publication suggested the term sub-PHS as a descriptor for those individuals who did not meet the above-specified clinical diagnostic criteria for GLI3-PHS but had some overlapping features and a pathogenic GLI3 variant consistent with the PHS pathogenetic mechanism (see Nomenclature).