Roentgen findings in homocystinuria

Enzyme replacement therapy prevents loss of bone and fat mass in murine homocystinuria

Skeletal and connective tissue defects are the most striking symptoms in patients suffering from classical homocystinuria (HCU). Here, we determined body composition and bone mass in three mouse models of HCU and assessed whether a long-term administration of enzyme replacement therapy (ERT) corrected the phenotype. The mouse models of HCU were analyzed using dual-energy X-ray absorptiometry and the data were complemented by plasma biochemical profiles. Both the mouse model lacking CBS (KO) and the one expressing human CBS mutant transgene on a mouse CBS null background (I278T) showed marked bone loss and decreased weight mostly due to a lower fat content compared with negative controls. In contrast, the HO mouse expressing the human CBS WT transgene on a mouse CBS null background showed no such phenotype despite similar plasma biochemical profile to the KO and I278T mice. More importantly, administration of ERT rescued bone mass and changes in body composition in the KO mice treated since birth and reversed bone loss and improved fat content in the I278T mice injected after the development of clinical symptoms. Our study suggests that ERT for HCU may represent an effective way of preventing the skeletal problems in patients without a restricted dietary regime.

Guidelines for the diagnosis and management of cystathionine beta-synthase deficiency

Cystathionine beta-synthase (CBS) deficiency is a rare inherited disorder in the methionine catabolic pathway, in which the impaired synthesis of cystathionine leads to accumulation of homocysteine. Patients can present to many different specialists and diagnosis is often delayed. Severely affected patients usually present in childhood with ectopia lentis, learning difficulties and skeletal abnormalities. These patients generally require treatment with a low-methionine diet and/or betaine. In contrast, mildly affected patients are likely to present as adults with thromboembolism and to respond to treatment with pyridoxine. In this article, we present recommendations for the diagnosis and management of CBS deficiency, based on a systematic review of the literature. Unfortunately, the quality of the evidence is poor, as it often is for rare diseases. We strongly recommend measuring the plasma total homocysteine concentrations in any patient whose clinical features suggest the diagnosis. Our recommendations may help to standardise testing for pyridoxine responsiveness. Current evidence suggests that patients are unlikely to develop complications if the plasma total homocysteine concentration is maintained below 120 μmol/L. Nevertheless, we recommend keeping the concentration below 100 μmol/L because levels fluctuate and the complications associated with high levels are so serious.

Bony changes of PKU neonates unrelated to phenylalanine levels

In 1962 bone abnormalities were described radiographically in phenylketonuria patients. Later, observations were made on PKU infants during the neonatal period, which allowed differentiation between inherited alterations in bone development from those changes due to dietary restriction. Similar changes have been described in other aminoacidurias. Wrist radiographs and serum phenylalanine levels were obtained on 73 patients first seen between 1965 and 1990. All radiographs were taken on the day of referral, when the patient was between 6 and 57 days old. Forty-nine patients were less than 28 days old. Bone abnormalities were present in 56 of 73 (77%) of the children, as compared to 0 of 16 in a control group. The presence or absence of bone abnormality is unrelated to serum phenylalanine level, and to the age of the children at referral. This finding suggests that the cause of these mesodermal changes is not a deviation of a single amino acid in the infant, but that they are caused by an intrauterine amino acid imbalance.

Angiographic findings in homocystinuria

Homocystinuria (HC) is an inborn error of amino acid metabolism characterized by ectopia lentis, mental retardation, and skeletal abnormalities. Vascular disorders may also occur in HC, although they are less common. Arteriographic studies of two sisters with HC are described. The younger woman's renal arteries showed wall irregularities and aneurysms, narrowing of the celiac and superior mesenteric arteries, and some aneurysmatic changes. In the older patient, irregular right carotid and splenic arteries were seen and a splenic aneurysm was present.