BackgroundPhenylketonuria (PKU) is an autosomal recessive disorder caused by the deficiency of phenylalanine hydroxylase that catalyzes the conversion of phenylalanine to tyrosine, using tetrahydrobiopterin (BH4) as coenzyme. Besides dietary phenylalanine restriction, new therapeutic options are emerging, such as the treatment with BH4 in subgroups of PKU patients responding to a loading test with BH4.MethodsA no-profit open-label interventional trial with long-term oral BH4 therapy, sponsored by the Italian Medicines Agency (AIFA), was performed in a group of 17 PKU patients resulted as BH4 responders among 46 subjects analyzed for BH4-responsiveness (prot. FARM5MATC7). We report on efficacy and safety data of BH4 therapy and analyze factors predicting BH4-responsiveness and long-term response to BH4. A BH4-withdrawal test was used as a proof of the efficacy of long-term therapy with BH4.ResultsForty-four percent of the patients responded to the 48 h-long loading test with BH4. All the phenotypic classes were represented. Genotype was the best predictor of responsiveness, along with lower phenylalanine levels at diagnosis, higher tolerance and lower phenylalanine/tyrosine ratio before the test. In BH4 responder patients, long-term BH4 therapy resulted safe and effective in increasing tolerance while maintaining a good metabolic control. The BH4 withdrawal test, performed in a subset of patients, showed that improved tolerance was directly dependent on BH4 assumption. Tolerance to phenylalanine was re-evaluated in 43.5% of patients and was longitudinally analyzed in 5 patients.ConclusionsLong-term treatment with BH4 is safe and effective in increasing tolerance to phenylalanine. There is real need to assess the actual tolerance to phenylalanine in PKU patients to ameliorate quality of life, improve nutritional status, avoiding unnecessarily restricted diets, and interpret the effects of new therapies for PKU.Electronic supplementary materialThe online version of this article (doi:10.1186/s13023-015-0227-8) contains supplementary material, which is available to authorized users.

Hyperphenylalaninemia (Online Mendelian Inheritance in Man ®database: 261600) is an autosomal recessive disorder mainly due to mutations in the gene for phenylalanine hydroxylase; the most severe form of hyperphenylalaninemia is classic phenylketonuria. We sequenced the entire gene for phenylalanine hydroxylase in 51 unrelated hyperphenylalaninemia patients from Southern Italy. The entire locus was genotyped in 46 out of 51 hyperphenylalaninemia patients, and 32 different disease‐causing mutations were identified. The pathologic nature of two novel gene variants, namely, c.707‐2delA and p.Q301P, was demonstrated by in vitro studies. c.707‐2delA is a splicing mutation that involves the accepting site of exon 7; it causes the complete skipping of exon 7 and results in the truncated p.T236MfsX60 protein. The second gene variant, p.Q301P, has very low residual enzymatic activity (∼ 4.4%), which may be ascribed, in part, to a low expression level (8–10%). Both the decreased enzyme activity and the low expression level are supported by analysis of the 3D structure of the molecule. The putative structural alterations induced by p.Q301P are compatible with protein instability and perturbance of monomer interactions within dimers and tetramers, although they do not affect the catalytic site. In vivo studies showed tetrahydrobiopterin responsiveness in the p.Q301P carrier but not in the c.707‐2delA carrier. We next investigated genotype–phenotype correlations and found that genotype was a good predictor of phenotype in 76% of patients. However, genotype–phenotype discordance occurred in approximately 25% of our patients, mainly those bearing mutations p.L48S, p.R158Q, p.R261Q and p.P281L.

Autoimmune polyendocrinopathy candidiasis ectodermal dystrophy (APECED), formerly known as autoimmune polyendocrine syndrome type 1, is a paradigm of a monogenic autoimmune disease caused by mutations of a gene, named autoimmune regulator (AIRE). AIRE acts as a transcription regulator that promotes immunological central tolerance by inducing the ectopic thymic expression of many tissue-specific antigens. Although the syndrome is a monogenic disease, it is characterized by a wide variability of the clinical expression with no significant correlation between genotype and phenotype. Indeed, many aspects regarding the exact role of AIRE and APECED pathogenesis still remain unraveled. In the last decades, several studies in APECED and in its mouse experimental counterpart have revealed new insights on how immune system learns self-tolerance. Moreover, novel interesting findings have extended our understanding of AIRE’s function and regulation thus improving our knowledge on the pathogenesis of APECED. In this review, we will summarize recent novelties on molecular mechanisms underlying the development of APECED and their clinical implications.

Mucopolysaccharidosis (MPS) IIIB (Sanfilippo syndrome, OMIM 252920) is a lysosomal storage disorder caused by the deficiency of a-N-acetylglucosaminidase (NAGLU), a lysosomal hydrolase involved in the degradation of heparan sulphate (HS) (1). MPS IIIB is characterized by multisystem involvement and a complex phenotype. The most debilitating manifestations of the disease are those related to central nervous system disease, with severe and progressive mental retardation, hyperactivity, and behavioral problems. Skeletal and visceral manifestations are less prominent, as compared with other MPS.Gastrointestinal manifestations, including diarrhea and constipation, have occasionally been described in patients with MPS IIIB, but they have been poorly characterized and their pathophysiology is not known.Although gastrointestinal symptoms are often overshadowed by the severe neurological phenotype, they may affect the quality of life of patients and of their families.We describe a case of MPS IIIB, referred to our hospital because of chronic diarrhea, in which abnormalities of intestinal endoscopy, histology, and scintigraphy with Tc-99m-labeled human serum albumin were found, partially overlapping with the features of intestinal lymphangiectasia. In this patient, a low-fat diet and supplementation of medium-chain triglycerides were started, leading to persisting improvement of diarrhea. These results add information on the pathophysiology of intestinal manifestations in MPS IIIB patients and possibly in other MPS patients with a history of chronic diarrhea. CASE REPORTWe describe a case of MPS IIIB, an 11-year-old Italian boy, born to healthy consanguineous parents, referred to our hospital at the age of 9 years because of developmental delay and severe chronic diarrhea. Besides parental consanguinity, family history was noncontributory. The first years of life were uneventful. Developmental delay was initially noticed at the age of 3 years. Gastrointestinal manifestations started at the age of 8 years.

We report on a female patient affected by galactosemia in whom the diagnosis was obscured by the concomitant presence of manifestations suggesting a cow’s milk intolerance. This case exemplifies the problems in reaching a correct diagnosis in patients with metabolic diseases.