Neu-Laxova syndrome

[2014 seems to have been a good year for Neu-Laxova syndrome]

Shaheen R, Rahbeeni Z, Alhashem A, Faqeih E, Zhao Q, Xiong Y, Almoisheer A, Al-Qattan SM, Almadani HA, Al-Onazi N, Al-Baqawi BS, Saleh MA, Alkuraya FS. Neu-Laxova syndrome, an inborn error of serine metabolism, is caused by mutations in PHGDH. Am J Hum Genet. 2014 Jun 5;94(6):898-904.

Abstract

Neu-Laxova syndrome (NLS) is a rare autosomal-recessive disorder characterized by severe fetal growth restriction, microcephaly, a distinct facial appearance, ichthyosis, skeletal anomalies, and perinatal lethality. The pathogenesis of NLS remains unclear despite extensive clinical and pathological phenotyping of the >70 affected individuals reported to date, emphasizing the need to identify the underlying genetic etiology, which remains unknown. In order to identify the cause of NLS, we conducted a positional-mapping study combining autozygosity mapping and whole-exome sequencing in three consanguineous families affected by NLS. Surprisingly, the NLS-associated locus identified in this study was solved at the gene level to reveal mutations in PHGDH, which is known to be mutated in individuals with microcephaly and developmental delay. PHGDH encodes the first enzyme in the phosphorylated pathway of de novo serine synthesis, and complete deficiency of its mouse ortholog recapitulates many of the key features of NLS. This study shows that NLS represents the extreme end of a known inborn error of serine metabolism and highlights the power of genomic sequencing in revealing the unsuspected allelic nature of apparently distinct clinical entities.

Acuna-Hidalgo R, Schanze D, Kariminejad A, Nordgren A, Kariminejad MH, Conner P, Grigelioniene G, Nilsson D, Nordenskjöld M, Wedell A, Freyer C, Wredenberg A, Wieczorek D, Gillessen-Kaesbach G, Kayserili H, Elcioglu N, Ghaderi-Sohi S, Goodarzi P, Setayesh H, van de Vorst M, Steehouwer M, Pfundt R, Krabichler B, Curry C, MacKenzie MG, Boycott KM, Gilissen C, Janecke AR, Hoischen A, Zenker M. Neu-Laxova syndrome is a heterogeneous metabolic disorder caused by defects in enzymes of the L-serine biosynthesis pathway. Am J Hum Genet. 2014 Sep 4;95(3):285-93.

Abstract

Neu-Laxova syndrome (NLS) is a rare autosomal-recessive disorder characterized by a recognizable pattern of severe malformations leading to prenatal or early postnatal lethality. Homozygous mutations in PHGDH, a gene involved in the first and limiting step in L-serine biosynthesis, were recently identified as the cause of the disease in three families. By studying a cohort of 12 unrelated families affected by NLS, we provide evidence that NLS is genetically heterogeneous and can be caused by mutations in all three genes encoding enzymes of the L-serine biosynthesis pathway. Consistent with recently reported findings, we could identify PHGDH missense mutations in three unrelated families of our cohort. Furthermore, we mapped an overlapping homozygous chromosome 9 region containing PSAT1 in four consanguineous families. This gene encodes phosphoserine aminotransferase, the enzyme for the second step in L-serine biosynthesis. We identified six families with three different missense and frameshift PSAT1 mutations fully segregating with the disease. In another family, we discovered a homozygous frameshift mutation in PSPH, the gene encoding phosphoserine phosphatase, which catalyzes the last step of L-serine biosynthesis. Interestingly, all three identified genes have been previously implicated in serine-deficiency disorders, characterized by variable neurological manifestations. Our findings expand our understanding of NLS as a disorder of the L-serine biosynthesis pathway and suggest that NLS represents the severe end of serine-deficiency disorders, demonstrating that certain complex syndromes characterized by early lethality could indeed be the extreme end of the phenotypic spectrum of already known disorders.

El-Hattab AW, Shaheen R, Hertecant J, Galadari HI, Albaqawi BS, Nabil A, Alkuraya FS. On the phenotypic spectrum of serine biosynthesis defects. J Inherit Metab Dis. 2016 May;39(3):373-81.

Abstract

L-serine is a non-essential amino acid that is de novo synthesized via the enzymes phosphoglycerate dehydrogenase (PGDH), phosphoserine aminotransferase (PSAT), and phosphoserine phosphatase (PSP). Besides its role in protein synthesis, L-serine is a precursor of a number of important compounds. Serine biosynthesis defects result from deficiencies in PGDH, PSAT, or PSP and have a broad phenotypic spectrum ranging from Neu-Laxova syndrome, a lethal multiple congenital anomaly disease at the severe end to a childhood disease with intellectual disability at the mild end, with infantile growth deficiency, and severe neurological manifestations as an intermediate phenotype. In this report, we present three subjects with serine biosynthesis effects. The first was a stillbirth with Neu-Laxova syndrome and a homozygous mutation in PHGDH. The second was a neonate with growth deficiency, microcephaly, ichthyotic skin lesions, seizures, contractures, hypertonia, distinctive facial features, and a homozygous mutation in PSAT1. The third subject was an infant with growth deficiency, microcephaly, ichthyotic skin lesions, anemia, hypertonia, distinctive facial features, low serine and glycine in plasma and CSF, and a novel homozygous mutation in PHGDH gene. Herein, we also review previous reports of serine biosynthesis defects and mutations in the PHGDH, PSAT1, and PSPH genes, discuss the variability in the phenotypes associated with serine biosynthesis defects, and elaborate on the vital roles of serine and the potential consequences of its deficiency.