Intra-familiar discordant PKU phenotype explained by mutation analysis in three pedigrees

Phenylalanine hydroxylase genotype-phenotype associations in the United States: A single center study

Phenylketonuria (PKU) is an autosomal recessive inborn error of metabolism caused by pathogenic variants in the phenylalanine hydroxylase gene (PAH). The correlation between genotype and phenotype can be complex and sometimes variable but often very useful for categorizing and predicting dietary tolerance and potential outcome. We reviewed medical records for 367 patients diagnosed with PKU or persistent mild hyperphenylalaninemia (MHP) between 1950 and 2015 who had PAH genotyping. In 351 we had the full PAH genotype as well as phenotypic characteristics such as phenylalanine (Phe) concentrations (at newborn screening, confirmation, and highest known), and dietary Phe tolerance. On 716 mutant chromosomes, including 14 in genotypes with only one identified variant, we identified 114 different pathogenic variants. The most frequent, p.R408W, was present in 15.4% of the alleles; other frequent variants were c.1315 + 1G > A (6.1%), p.I65T (5.7%), and p.R261Q (5.7%). Three variants, c.142 T > G (p.L48 V), c.615G > C (p.E205D), and c.1342_1345delCTCC, were novel. We used the phenotypic parameters of variants paired with null alleles (functional hemizygotes) to assign the variants as classic PKU, moderate PKU, mild PKU, MHP-gray zone, or MHP. We also included the phenotype association(s) for all of the full genotypes. In 103 patients, we also could assign sapropterin dihydrochloride responsiveness, which is a synthetic form of the tetrahydrobiopterin (BH4) PAH cofactor. This compilation from a single metabolic center provides further information on PAH variants in the United States and the correlations between genotype and phenotype.

Prospective evaluation of pregnancy outcome in an Italian woman with late-onset combined homocystinuria and methylmalonic aciduria

BACKGROUND

Cobalamin metabolism disorders are rare, inherited diseases which cause megaloblastic anaemia and other clinical manifestations. Early diagnosis of these conditions is essential, in order to allow appropriate treatment as early as possible.

CASE PRESENTATION

Here we report the case of a patient who was apparently healthy until the age of 20, when she presented with impaired renal function and normocytic anaemia. At the age of 34, when her first pregnancy resulted in an intrauterine death of a morphologically normal growth-restricted foetus, she was diagnosed with homocystinuria and methylmalonic aciduria due to cyanocobalamin C (cblC) defect, which was confirmed by molecular investigation. Consequently, hydroxocobalamin was administered to correct homocysteine plasma levels. This treatment was efficacious in lowering homocysteine plasma levels and restored anaemia and renal function. During a second pregnancy, the patient was also administered a prophylactic dose of low molecular -weight heparin. The pregnancy concluded with a full-term delivery of a healthy male.

CONCLUSIONS

This case emphasises the importance of awareness and appropriate management of rare metabolic diseases during pregnancy. We suggest that women with late-onset cblC defect can have a positive pregnancy outcome if this metabolic disease is treated adequately.