Phenotype and genotype of 23 patients with hypopituitarism and pathogenic GLI2 variants

OBJECTIVE

To analyze the phenotype and genotype of patients with congenital hypopituitarism (CH) and pathogenic (P) GLI2 variants.

METHODS

A large cohort of patients with hypopituitarism was screened for GLI2 variants using a next-generation sequencing panel. Genotype-phenotype correlations were then assessed using GENHYPOPIT phenotypic data.

RESULTS

Of the 39 GLI2 variants identified in 717 index cases, 17 were classified as pathogenic and likely pathogenic. All these GLI2 variants were identified in 23 patients (17 index cases and 6 relatives) with associated pituitary stalk interruption syndrome or extrapituitary manifestations. GLI2 variants were the most frequently identified genetic cause in patients with syndromic hypopituitarism (68%): 88% (15/17) of mutations were truncating variants, and 45% were de novo. Most patients with a GLI2 variant (21/23, 91%) had hypopituitarism, including 21.7% (5/23) presenting isolated growth hormone deficiency. Two patients had Kallmann syndrome. Pituitary morphological abnormalities were present in 84% of the patients with P GLI2 variants (index cases and affected relatives). The remaining signs included neurocognitive disorders (38%), hexadactyly (27%), cardiac septal defects, and renal/vesical abnormalities. A possible digenic origin (GLI2/HESX1) is proposed in one family.

CONCLUSION

In this large multicentric international cohort, GLI2 was the most frequently identified genetic cause of syndromic CH with constant association of pituitary stalk interruption syndrome or extrapituitary clinical features. In addition to polydactyly and neurocognitive disorders, cardiac and renal abnormalities were also frequently observed and should be investigated further. The variable expression of GLI2-associated phenotypes justifies further research in this area.

Identification of disease-relevant modulators of the SHH pathway in the developing brain

Pathogenic gene variants in humans that affect the sonic hedgehog (SHH) pathway lead to severe brain malformations with variable penetrance due to unknown modifier genes. To identify such modifiers, we established novel congenic mouse models. LRP2-deficient C57BL/6N mice suffer from heart outflow tract defects and holoprosencephaly caused by impaired SHH activity. These defects are fully rescued on a FVB/N background, indicating a strong influence of modifier genes. Applying comparative transcriptomics, we identified Pttg1 and Ulk4 as candidate modifiers upregulated in the rescue strain. Functional analyses showed that ULK4 and PTTG1, both microtubule-associated proteins, are positive regulators of SHH signaling, rendering the pathway more resilient to disturbances. In addition, we characterized ULK4 and PTTG1 as previously unidentified components of primary cilia in the neuroepithelium. The identification of genes that powerfully modulate the penetrance of genetic disturbances affecting the brain and heart is likely relevant to understanding the variability in human congenital disorders.