A point mutation (c.323C>T) in the ALPL gene leading to a proline to leucine substitution at position 108 of TNSALP was first reported in a patient diagnosed with odonto-HPP (M Herasse et al., J Med Genet 2003;40:605-609), although the effects of this mutation on the TNSALP molecule have not been elucidated.
In vitro testing showed that one mutation, T117H, produced an ALP protein with almost no enzyme activity; the second, G438S, produced a protein with normal activity, but its activity was inhibited by raising the media phosphate concentration, suggesting that phosphate retention (attributable to uremia) could have contributed to the phenotypic change, although a pathogenic effect of bisphosphonate treatment is also likely.
In vitro testing showed that one mutation, T117H, produced an ALP protein with almost no enzyme activity; the second, G438S, produced a protein with normal activity, but its activity was inhibited by raising the media phosphate concentration, suggesting that phosphate retention (attributable to uremia) could have contributed to the phenotypic change, although a pathogenic effect of bisphosphonate treatment is also likely.
Patients with the p.F327L compound heterozygous mutation had the different non-lethal type with short stature and a gradual improvement in ALP level and bone mineralisation.
The SNV c.1190-65C>A (rs1780329, minor allele frequency (MAF) patients: 0.17; controls: 0.11; P=0.04) in the ALP gene was significantly more frequent in PXE patients.
A point mutation (c.1250A>G), which leads to replacement of an asparagine at position 417 of TNSALP with serine [TNSALP (N417S)], has been reported in a patient diagnosed with perinatal HPP (Sergi C. et al.Am, J. Med.Genet.103, 235-240, 2001).
Nevertheless, the probands (compound heterozygous: p.[N440del];[R152C]) feature early-onset and severe odonto-HPP phenotype, whereas the father (p.[N440del];[=]) has only moderate symptoms, suggesting p.R152C may contribute or predispose to a more severe dental phenotype in combination with the deletion.
Our study shows that the novel de novo splicing mutation c.298-1G>A in intron 4 and the missense mutation c.1271T>C in exon 11 of the ALPL gene are responsible for hypophosphatasia in some Chinese patients.
Missense mutations at position 420 of TNSALP (standard nomenclature), which convert glycine to serine [TNSALP (G420S)] or alanine [TNSALP (G420A)], have been reported in perinatal and childhood HPP, respectively.
Our results indicate that the TNAP haplotype rs3767155 (G)/rs3738099 (G)/rs1780329 (T) is a novel genetic marker in men that is significantly associated with AS in multiplex families containing affected individuals of both sexes.
Our results indicate that the TNAP haplotype rs3767155 (G)/rs3738099 (G)/rs1780329 (T) is a novel genetic marker in men that is significantly associated with AS in multiplex families containing affected individuals of both sexes.
Our results indicate that the TNAP haplotype rs3767155 (G)/rs3738099 (G)/rs1780329 (T) is a novel genetic marker in men that is significantly associated with AS in multiplex families containing affected individuals of both sexes.
Thus, loss of function resulting from the interchain disulfide bridge is the molecular basis for the lethal hypophosphatasia associated with TNSALP(R433C).
Homozygosity for TNSALP mutation 1348c>T (Arg433Cys) causes infantile hypophosphatasia manifesting transient disease correction and variably lethal outcome in a kindred of black ancestry.
Substitution of an arginine at position 433 with a histidine [TNSALP(R433H)] or a cysteine [TNSALP(R433C)] was reported in patients diagnosed with the mild or severe form of hypophosphatasia, respectively.
This study indicated that the mutant (A115V) TNSALP gene produced the defective ALP enzyme and it could be recessively transmitted and be a disease-causing mutation of the adult-type hypophosphatasia.
Phenotype/genotype correlation indicates that G309R is a deleterious mutation that can lead to seizures and a lethal outcome, as was demonstrated in our patient.