Xia-Gibbs syndrome (XGS) is a recently described neurodevelopmental disorder due to heterozygous loss-of-function AHDC1 mutations. XGS is characterized by global developmental delay, intellectual disability, hypotonia, and sleep abnormalities. Here we report the clinical phenotype of five of six individuals with XGS identified prospectively at the Children's Hospital of Philadelphia, a tertiary children's hospital in the USA. Although all five patients demonstrated common clinical features characterized by developmental delay and characteristic facial features, each of our patients showed unique clinical manifestations. Patient one had craniosynostosis; patient two had sensorineural hearing loss and bicuspid aortic valve; patient three had cutis aplasia; patient four had soft, loose skin; and patient five had a lipoma. Differential diagnoses considered for each patient were quite broad, and included craniosynostosis syndromes, connective tissue disorders, and mitochondrial disorders. Exome sequencing identified a heterozygous, de novo AHDC1 loss-of-function mutation in four of five patients; the remaining patient has a 357kb interstitial deletion of 1p36.11p35.3 including AHDC1. Although it remains unknown whether these unique clinical manifestations are rare symptoms of XGS, our findings indicate that the diagnosis of XGS should be considered even in individuals with additional non-neurological symptoms, as the clinical spectrum of XGS may involve such non-neurological manifestations. Adding to the growing literature on XGS, continued cohort studies are warranted in order to both characterize the clinical spectrum of XGS as well as determine standard of care for patients with this diagnosis.

Kaufman oculocerebrofacial syndrome (KOS) is a recessive neurodevelopmental disorder characterized by intellectual disability and lack of speech. KOS is caused by inactivating mutations in UBE3B, but the underlying biological mechanisms are completely unknown. We found that loss of Ube3b in mice resulted in growth retardation, decreased grip strength, and loss of vocalization. The brains of Ube3b−/− mice had hypoplasia of the corpus callosum, enlarged ventricles, and decreased thickness of the somatosensory cortex. Ube3b−/− cortical neurons had abnormal dendritic morphology and synapses. We identified 22 UBE3B interactors and found that branched-chain α-ketoacid dehydrogenase kinase (BCKDK) is an in vivo UBE3B substrate. Since BCKDK targets several metabolic pathways, we profiled plasma and cortical metabolomes from Ube3b−/− mice. Nucleotide metabolism and the tricarboxylic acid cycle were among the pathways perturbed. Substrate-induced mitochondrial respiration was reduced in skeletal muscle but not in liver of Ube3b−/− mice. To assess the relevance of these findings to humans, we identified three KOS patients who had compound heterozygous UBE3B mutations. We discovered changes in metabolites from similar pathways in plasma from these patients. Collectively, our results implicate a disease mechanism in KOS, suggest that it is a metabolic encephalomyopathy, and provide an entry to targeted therapies.

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Tyrosinaemia I (fumarylacetoacetate hydrolase deficiency) is an autosomal recessive inborn error of tyrosine metabolism that produces liver failure in infancy or a more chronic course of liver disease with cirrhosis, often complicated by hepatocellular carcinoma, in childhood or early adolescence. We studied a 37-year-old woman with tyrosinaemia I whose severe liver disease in infancy and rickets during childhood resolved with dietary therapy. From 14 years of age she resumed an unrestricted diet with the continued presence of the biochemical features of tyrosinaemia, yet maintained normal liver function. In adult years she accumulated only small amounts of succinylacetone. Despite this evolution to a mild biochemical and clinical phenotype, she eventually developed hepatocellular carcinoma. Her fumarylacetoacetate hydrolase genotype consists of a splice mutation, IVS6-1g>t, and a novel missense mutation, Q279R. Studies of resected liver demonstrated the absence of hydrolytic activity and of immunological expression of fumarylacetoacetate hydrolase in liver tumour. In nontumoral areas, however, 53% of normal hydrolytic activity and immunologically present fumarylacetoacetate hydrolase was found. This case demonstrates the high risk of liver cancer in tyrosinaemia I even in a seemingly favourable biological environment.