Primary hyperoxaluria type 1 (PH1) is caused by deficiency of the liver peroxisomal enzyme alanine-glyoxylate aminotransferase (AGT), which catalyzes the conversion of glyoxylate to glycine. When AGT activity is reduced or absent, glyoxylate is converted to oxalate, which cannot be metabolized and must be excreted by the kidneys. Insoluble calcium oxalate crystals form due to high urinary oxalate concentration. Urinary crystals aggregate, leading to nephrolithiasis (i.e., calcium oxalate kidney stones) in the renal pelvis / urinary tract; often the crystals deposit in kidney parenchyma (nephrocalcinosis). The age at presentation of PH1 ranges from infancy (age <12 months) in 10% of individuals, childhood/adolescence (age 1-17 years) in 70%, and adulthood (age =18 years) in 20%. The natural history of untreated PH1 is (1) progressive decline in kidney function due to complications of nephrolithiasis (e.g., urinary obstruction, infection) and nephrocalcinosis, and (2) in persons with advanced chronic kidney disease (CKD), high plasma oxalate concentrations result in other organ and tissue damage from calcium oxalate deposition (i.e., "oxalosis"), most commonly in the bones, heart, and retina. In the absence of treatment, progression of oxalosis results in death from kidney failure and/or other organ involvement.

Primary hyperoxaluria type 2 (PH2), caused by deficiency of the enzyme glyoxylate reductase/hydroxypyruvate reductase (GR/HPR), is characterized by recurrent nephrolithiasis (deposition of calcium oxalate in the renal pelvis / urinary tract), nephrocalcinosis (deposition of calcium oxalate in the renal parenchyma), and end-stage kidney disease (ESKD). After ESKD, oxalosis (widespread tissue deposition of calcium oxalate) usually develops. Symptom onset is typically in childhood.

5-Oxoprolinuria can be caused by genetic defects in either of 2 enzymes involved in the gamma-glutamyl cycle of glutathione metabolism: glutathione synthetase (GSS; 601002) or 5-oxoprolinase (OPLAH; 614243). GSS deficiency (266130) is best characterized as an inborn error of glutathione metabolism, but there is debate as to whether OPLAH deficiency represents a disorder or simply a biochemical condition with no adverse clinical effects because patients lack a consistent clinical picture apart from 5-oxoprolinuria (summary by Calpena et al., 2013).

The imino acids, proline and hydroxyproline, share a renal tubular reabsorptive mechanism with glycine. Iminoglycinuria (IG; 242600), a benign inborn error of amino acid transport, is also a normal finding in neonates and infants under 6 months of age (Chesney, 2001). Early studies of families with iminoglycinuria suggested genetic complexity, with homozygotes developing IG and heterozygotes manifesting only hyperglycinuria (HG) (summary by Broer et al., 2008). A phenotype of combined glucosuria and glycinuria has been described (see 138070).

Primary hyperoxaluria is an autosomal recessive disorder of glyoxylate metabolism that results in excessive endogenous oxalate synthesis and the formation of calcium oxalate kidney stones. Progressive renal inflammation and interstitial fibrosis from advanced nephrocalcinosis, recurrent urolithiasis, and urinary tract infections can cause reduced renal function, systemic oxalate deposition, and end-stage renal failure. Compared to hyperoxaluria type I (HP1; 259900) and type II (HP2; 260000), HP3 appears to be the least severe, with good preservation of kidney function in most patients. The typical clinical characteristic is early onset of recurrent urolithiasis, but less active stone formation later (summary by Wang et al., 2015). For a discussion of genetic heterogeneity of primary hyperoxaluria, see 259900.

Macrocephaly refers to an abnormally enlarged head inclusive of the scalp, cranial bones, and intracranial contents. Macrocephaly may be due to megalencephaly (true enlargement of the brain parenchyma), and the 2 terms are often used interchangeably in the genetic literature (reviews by Olney, 2007 and Williams et al., 2008). Autosomal recessive macrocephaly/megalencephaly syndrome is characterized by an enlarged cranium apparent at birth or in early childhood. Affected individuals have intellectual disability and may have dysmorphic facial features resulting from the macrocephaly (summary by Alfaiz et al., 2014).