Familial hyperprolinemia and mental retardation. A second metabolic type

Psychiatric phenotypes associated with hyperprolinemia: A systematic review

Hyperprolinemia Type I and II are genetic metabolic disorders caused by disrupted proline degradation. It has been suggested that hyperprolinemia is associated with increased risk of developmental and mental disorders but detailed information on the psychiatric phenotype in hyperprolinemic patients is limited. Following PRISMA guidelines, we carried out a systematic review to clarify psychiatric phenotypes in patients with hyperprolinemia. We screened 1753 studies and included 35 for analysis, including 20 case reports and 15 case-control and cohort studies. From these studies, a common psychiatric phenotype is observed with a high prevalence of developmental delay, intellectual disability, autism spectrum disorders, and psychosis spectrum disorders. In most cases, a genetic cause of hyperprolinemia was known, these included mutations in the PRODH and ALDH4A1 genes and deletions of chromosome 22q11.2. No evidence for a biochemical phenotype-clinical phenotype correlation was found; that is, no association between higher proline levels and specific psychiatric phenotypes was observed. This suggests that genomic and environmental factors are likely to contribute to clinical outcomes. More studies are needed to clarify whether hyperprolinemia is a primary causal factor underlying the increased risk of developing psychiatric disorders seen in patients with hyperprolinemia, or whether hyperprolinemia and psychiatric disorders are both consequences of a shared underlying mechanism.

Early neurological phenotype in 4 children with biallelic PRODH mutations

Hyperprolinemia type I (HPI) results from a deficiency of proline oxidase (POX), involved in the first step in the conversion of proline to glutamate. Diverse phenotypes were described in patients with HPI, prior to the identification of the POX gene (PRODH): whereas various patients were asymptomatic, others had neurological and extraneurological defects. The PRODH gene is located in the region deleted in velocardiofacial syndrome (VCFS). Heterozygous and homozygous mutations have been identified in patients with variable hyperprolinemia and various features (patients with schizophrenia, chromosome 22q11 microdeletions and/or neurological defects). A functional study has divided the PRODH missense mutations into three groups: those leading to mild, moderate, or severe reduction of POX activity. In this study, we report four unrelated children with HPI and a homogeneous severe neurological phenotype. We identified biallelic abnormalities in PRODH in these patients that led to severe reduction of POX activity. These included missense and non-sense mutations, deletions of PRODH and a 22q11 microdeletion. Four other children have been reported with severe biallelic PRODH mutations. The phenotype of these eight patients associates early psychomotor development delay with predominant cognitive defects, autistic features and epilepsy. Their values of hyperprolinemia ranged from 400 to 2200 micromol/L. Patients with biallelic PRODH alterations resulting in severely impaired POX activity had an early onset and severe neurological features. Thus, children with this phenotype and those with a microdeletion in chromosome 22q11, especially those with mental retardation and autistic features, should be tested for hyperprolinemia. Hyperprolinemic patients should be screened for PRODH mutations.

Lysosomal amino acid transporter LYAAT-1 in the rat central nervous system: an in situ hybridization and immunohistochemical study

A first mammalian lysosomal transporter (LYAAT-1) was recently identified and functionally characterized. Preliminary immunocytochemical data revealed that LYAAT-1 localizes to lysosomes in some neurons. In order to determine whether it is expressed in specific neuron populations and other cell types, and to confirm whether it is localized at the membrane of lysosomes, we used in situ hybridization and immunohistochemistry methods in adult rat central nervous system (CNS). We found that LYAAT-1 is expressed in most areas of the CNS, specifically in neurons, but also in choroid plexus and ependymal epithelium cells. LYAAT-1-IR (immunoreactivity) levels varied among different neuroanatomical structures but were present in neurons independently of the neurotransmitter used (glutamate, GABA, acetylcholine, noradrenaline, serotonin, or glycine). Light and confocal microscopy demonstrated that LYAAT-1 and the lysosomal marker cathepsin D colocalized throughout the brain and electron microscopy showed that LYAAT-1-IR was associated with lysosomal membranes. In addition, LYAAT-1-IR was also found associated with other membranes belonging to the Golgi apparatus and lateral saccules and less frequently with multivesicular bodies, endoplasmic reticulum, and occasionally with the plasma membrane. The localization of LYAAT-1 at the lysosomal membrane is consistent with the view that it mediates amino acid efflux from lysosomes. Furthermore, its cell expression pattern suggests that it may contribute to specialized cellular function in the rat CNS such as neuronal metabolism, neurotransmission, and control of brain amino acid homeostasis.

Proline in the cerebrospinal fluid of normal subjects and Alzheimer's-disease patients, as determined with a new double-labeling assay technique

Past studies have implicated proline involvement in the function of memory and learning. A new micromethod has been developed that is suitable for measuring proline accurately in as little as 0.1 ml of CSF. In normal human CSF, the average proline level was found to be consistently about 1.3 microM. In the CSF of patients with Alzheimer's disease and mixed dementias, the levels of proline showed no statistically significant difference from proline levels in the CSF of normal controls. Furthermore, the proline levels in the CSF of the Alzheimer's disease patients did not reflect, consistently, the cognitive deficits or the symptomatic severity of the disease. Proline levels in CSF showed no statistically significant change with the age of individuals tested.

The transport and metabolism of L-proline-14C in the rat in vivo

The physiologic disposition, metabolic fate, and renal clearance of intravenously injected 14C-L-proline was determined in the rat. The disappearance of radioactivity from plasma occurred with a biphasic curve, the initial high levels reaching a nadir about 30 min after injection with subsequent increasing amounts of radioactivity. Examination of the 14C components in plasma revealed that 14C-proline disappeared rapidly during the first 30 min. At this time, the labeling of circulating plasma proteins ensued and continued to increase during the following 45 min of observations. Plasma glucose became labeled 10 min after injection and, thereafter, increased its 14C content. The extensive labeling of plasma proteins and glucose accounted for the increasing 14C found in plasma 30 min after injection. The course of radioactive labeling of brain, kidney, diaphragm, and liver was assessed. The greatest number of cpm/mg of tissue was found in the kidney. Determination of the distribution ratio, the ratio of cpm/ml intracellular nonprotein 14C to that in plasma in kidney revealed a peak of 3.9 within 15 min, a value comparable to that found in vitro. Twelve percent of the administered radioactivity was excreted as 14CO2 within 180 min. The oxidation was inhibited by known transport and metabolic inhibitors, the greatest effect observed with hydroxyproline, followed in order by thioproline, 3,4-dihydroproline, and glycine. The fractional urinary excretion of proline, Cproline/Cinulin, was determined and found to be 1% or less. This was increased by inhibitors, the greatest effect due to hydroxyproline followed in order by dehydroproline and glycine, a result similar to the observed extent of inhibition of proline oxidation to 14C O2. The physiologic disposition of proline was not altered by ligation of the renal vasculature.

Type II hyperprolinemia. Delta1-pyrroline-5-carboxylic acid dehydrogenase deficiency in cultured skin fibroblasts and circulating lymphocytes

Type II hyperprolinemia is an inherited abnormality in amino acid metabolism characterized by elevated plasma proline concentrations, iminoglycinuria, and the urinary excretion of delta1-pyrroline compounds. To define the enzymologic defect of this biochemical disorder, we developed a specific, sensitive radioisotopic assay for the proline degradative enzyme delta1-pyrroline-5-carboxylic acid dehydrogenase. Using this assay, we have shown an absence of delta1-pyrroline-5-carboxylic acid dehydrogenase activity in the cultured fibroblasts from three patients with type II hyperprolinemia. We confirmed this result on cultured cells by demonstrating a similar absence of delta1-pyrroline-5-carboxylic acid dehydrogenase activity in extracts prepared from the peripheral leukocytes of these patients. Additionally, we found significantly decreased levels of delta1-pyrroline-5-carboxylic acid dehydrogenase activity in the leukocyte extracts from five obligate heterozygotes for type II hyperprolinemia. We also demonstrated a reduction in leukocyte delta1-pyrroline-5-carboxylic acid dehydrogenase activity in three successive generations of a family. These results prove that an absence of delta1-pyrroline-5-carboxylic acid dehydrogenase is the enzymologic defect in type II hyperprolinemia and that this defect is inherited in an autosomal recessive fashion.

Hyperprolinaemia: a disease which does not need treatment?

The authors observed two cases of hyperprolinaemia (one of type I and the other of type II) which were asymptomatic. The anomalies described up to the present time in association with hyperprolinaemia are inconstant, nonspecific, and extremely heterogeneous. This suggests that the relationship between hyperprolinaemia and other anomalies is purely coincidental, and that a therapeutic approach by diet is unjustified.

Asymptomatic type II hyperprolinaemia associated with hyperglycinaemia in three sibs

Three clinically normal sibs were discovered to have type II hyperprolinaemia in a routine serum amino acid screening programme in Sicily. In addition to the basic biochemical features of type II hyperprolinaemia, all 3 children had marked hyperglycinaemia, whereas their parents had both normal blood proline and glycine concentrations. Clinical normality in individuals with hyperprolinaemia may suggest that these two metabolic disorders (types I and II) are benign entities. Furthermore, the absence of clinical abnormality in these sibs, despite the presence of marked hyperprolinaemia and hyperglycinaemia, may suggest that neither of these findings alone causes brain damage. The hyperglycinaemia in these sibs is unexplained and is an unusual if not unique finding in association with hyperprolinaemia.