Pitfalls in the Diagnosis of Hereditary Fructose Intolerance

Establishing the diagnosis of hereditary fructose intolerance (HFI) remains difficult despite the availability of specific molecular genetic testing of the ALDOB gene. This is attributable, at least in part, to the lack of a specific and practical biomarker. We report the incidental diagnosis of HFI as a consequence of nontargeted genetic testing ordered for alternative indications in 5 patients, including 3 children and 2 adults. Two of the children were diagnosed with HFI after extensive evaluations that ultimately involved clinical or research exome sequencing. The third child was diagnosed with HFI during subsequent genetic testing of at-risk family members. Both adults learned to avoid fructose and remained asymptomatic of HFI before diagnosis. One was diagnosed with HFI during preconception, nontargeted expanded carrier screening. For the other, concern for HFI was initially raised by indeterminate direct-to-consumer genetic testing results. None of these patients presented with infantile acute liver failure or other acute decompensation. Our findings suggest that the emphasis of classic teaching on infantile liver failure after first exposure to fructose may be inadvertently increasing the likelihood of missing cases of HFI characterized by other manifestations. HFI is likely underdiagnosed and should be considered for patients with nonspecific findings as well as for individuals with significant aversion to sweets.

Relapsing-remitting clinical course expands the phenotype of Aicardi-Goutières syndrome

Aicardi-Goutières syndrome (AGS) is a rare and likely underdiagnosed genetic leukoencephalopathy, typically presenting in infancy with encephalopathy and characteristic neuroimaging features, with residual static neurological deficits. We describe a patient who, following an initial presentation at the age of 12 months in keeping with AGS, exhibited a highly atypical relapsing course of neurological symptoms in adulthood with essentially normal neuroimaging. Whole-exome sequencing confirmed a pathogenic RNASEH2B gene variant consistent with AGS. This case highlights the expanding phenotypes associated with AGS and the potential role of whole-exome sequencing in facilitating an increase in the rate of diagnosis.

Xia-Gibbs syndrome in adulthood: a case report with insight into the natural history of the condition

A 55-yr-old male with severe intellectual disability, behavioral problems, kyphoscoliosis, and dysmorphic features was referred for a genetic evaluation. Chromosomal microarray, RASopathy gene panel, mitochondrial sequencing, and fragile X testing were all negative. Subsequent whole-exome sequencing revealed a heterozygous, truncating variant in the AHDC1 gene, consistent with a diagnosis of Xia-Gibbs syndrome (XGS). Review of his clinical history showed many classic dysmorphic and clinical features of XGS, but no major health issues in adulthood other than intellectual disability. This individual is the oldest published XGS case to date, demonstrates the wide phenotypic spectrum of the disorder, and provides information on the condition's natural history. As more adults undergo genomic studies, we will continue to learn about the adult phenotypes of genetic conditions typically diagnosed in the pediatric setting.

Genetic variants in the KDM6B gene are associated with neurodevelopmental delays and dysmorphic features

Lysine-specific demethylase 6B (KDM6B) demethylates trimethylated lysine-27 on histone H3. The methylation and demethylation of histone proteins affects gene expression during development. Pathogenic alterations in histone lysine methylation and demethylation genes have been associated with multiple neurodevelopmental disorders. We have identified a number of de novo alterations in the KDM6B gene via whole exome sequencing (WES) in a cohort of 12 unrelated patients with developmental delay, intellectual disability, dysmorphic facial features, and other clinical findings. Our findings will allow for further investigation in to the role of the KDM6B gene in human neurodevelopmental disorders.

Growth hormone deficiency, aortic dilation, and neurocognitive issues in Feingold syndrome 2

We report three patients with Feingold 2 syndrome with the novel features of growth hormone deficiency associated with adenohypophyseal compression, aortic dilation, phalangeal joint contractures, memory, and sleep problems in addition to the typical features of microcephaly, brachymesophalangy, toe syndactyly, short stature, and cardiac anomalies. Microdeletions of chromosome 13q that include the MIR17HG gene were found in all three. One of the patients was treated successfully with growth hormone. In addition to expanding the phenotype of Feingold 2 syndrome, we suggest management of patients with Feingold 2 syndrome include echocardiography at the time of diagnosis in all patients and consideration of evaluation for growth hormone deficiency in patients with short stature.