chr1-21575777-G-A

Position:

• chr1-21575777-G-A

Variant summary

Our verdict is Likely pathogenic. Variant got 9 ACMG points: 9P and 0B. PM1 PM2 PP3_Strong PP5

The ENST00000374840.8(ALPL):​c.1042G>A​(p.Ala348Thr) variant causes a missense change involving the alteration of a conserved nucleotide. The variant was absent in control chromosomes in GnomAD project. In-silico tool predicts a pathogenic outcome for this variant. Variant has been reported in ClinVar as Conflicting classifications of pathogenicity (no stars).

• Frequency: Genomes: not found (cov: 32)
• Consequence: ALPL ENST00000374840.8 missense
• Clinical Significance: Conflicting classifications of pathogenicity criteria provided, conflicting classifications P:2 U:3
• Conservation: PhyloP100: 10.0

Genes affected

ALPL (HGNC:438): (alkaline phosphatase, biomineralization associated) This gene encodes a member of the alkaline phosphatase family of proteins. There are at least four distinct but related alkaline phosphatases: intestinal, placental, placental-like, and liver/bone/kidney (tissue non-specific). The first three are located together on chromosome 2, while the tissue non-specific form is located on chromosome 1. The product of this gene is a membrane bound glycosylated enzyme that is not expressed in any particular tissue and is, therefore, referred to as the tissue-nonspecific form of the enzyme. Alternative splicing results in multiple transcript variants, at least one of which encodes a preproprotein that is proteolytically processed to generate the mature enzyme. This enzyme may play a role in bone mineralization. Mutations in this gene have been linked to hypophosphatasia, a disorder that is characterized by hypercalcemia and skeletal defects. [provided by RefSeq, Oct 2015]

ACMG classification

Verdict is Likely_pathogenic. Variant got 9 ACMG points.

• PM1: In a hotspot region, there are 3 aminoacids with missense pathogenic changes in the window of +-8 aminoacids around while only 0 benign, 8 uncertain in ENST00000374840.8
• PM2: Very rare variant in population databases, with high coverage
• PP3: MetaRNN computational evidence supports a deleterious effect, 0.99
• PP5: Variant 1-21575777-G-A is Pathogenic according to our data. Variant chr1-21575777-G-A is described in ClinVar as [Conflicting_classifications_of_pathogenicity]. Clinvar id is 555880.We mark this variant Likely_pathogenic, oryginal submissions are: {Likely_pathogenic=1, Pathogenic=1, Uncertain_significance=2}. Variant chr1-21575777-G-A is described in Lovd as [Pathogenic].

Transcripts

RefSeq

Gene	Transcript	HGVSc	HGVSp	Effect	#exon/exons	MANE	Protein	UniProt
ALPL	NM_000478.6	c.1042G>A	p.Ala348Thr	missense_variant	10/12	ENST00000374840.8	NP_000469.3

Ensembl

Gene	Transcript	HGVSc	HGVSp	Effect	#exon/exons	TSL	MANE	Protein	Appris	UniProt
ALPL	ENST00000374840.8	c.1042G>A	p.Ala348Thr	missense_variant	10/12	1	NM_000478.6	ENSP00000363973	P1

Frequencies

GnomAD3 genomes Cov.: 32

GnomAD4 exome Cov.: 32

GnomAD4 genome Cov.: 32

ClinVar

Significance: Conflicting classifications of pathogenicity

Submissions summary: Pathogenic:2 Uncertain:3

Revision: criteria provided, conflicting classifications

Submissions by phenotype

Adult hypophosphatasia Pathogenic:1

Likely pathogenic, criteria provided, single submitter

clinical testing

Baylor Genetics

Jun 01, 2023

- -

not provided Pathogenic:1

Pathogenic, criteria provided, single submitter

clinical testing

Labcorp Genetics (formerly Invitae), Labcorp

Jan 25, 2024

This sequence change replaces alanine, which is neutral and non-polar, with threonine, which is neutral and polar, at codon 348 of the ALPL protein (p.Ala348Thr). This variant is not present in population databases (gnomAD no frequency). This missense change has been observed in individual(s) with autosomal recessive hypophosphatasia (PMID: 10679946, 11855933, 32160374). This variant is also known as A331T. ClinVar contains an entry for this variant (Variation ID: 555880). Advanced modeling of protein sequence and biophysical properties (such as structural, functional, and spatial information, amino acid conservation, physicochemical variation, residue mobility, and thermodynamic stability) performed at Invitae indicates that this missense variant is expected to disrupt ALPL protein function with a positive predictive value of 95%. Experimental studies have shown that this missense change affects ALPL function (PMID: 10679946). For these reasons, this variant has been classified as Pathogenic. -

not specified Uncertain:1

Uncertain significance, criteria provided, single submitter

clinical testing

Women's Health and Genetics/Laboratory Corporation of America, LabCorp

May 16, 2023

Variant summary: ALPL c.1042G>A (p.Ala348Thr) results in a non-conservative amino acid change in the encoded protein sequence. Five of five in-silico tools predict a damaging effect of the variant on protein function. The variant was absent in 251440 control chromosomes (gnomAD). c.1042G>A has been reported in the literature in compound heterozygous individuals affected with Hypophosphatasia (Taillandier_2000, Mumm_2002, Del Angel_2020). These data indicate that the variant may be associated with disease. The variant was found impacting protein function by reducing enzymatic activity to 33% compared to wild-type (Taillandier_2000). The following publications have been ascertained in the context of this evaluation (PMID: 32160374, 11855933, 10679946). Two ClinVar submitters have assessed the variant since 2014: one classified the variant as uncertain significance, and one as likely pathogenic. Based on the evidence outlined above, the variant was classified as VUS-possibly pathogenic. -

ALPL-related disorder Uncertain:1

Uncertain significance, no assertion criteria provided

clinical testing

PreventionGenetics, part of Exact Sciences

Jan 11, 2024

The ALPL c.1042G>A variant is predicted to result in the amino acid substitution p.Ala348Thr. This variant in the compound heterozygous condition along with a second variant in this gene was reported in several individuals with hypophosphatasia (reported as Ala331Thr, Taillandier et al. 2000. PubMed ID: 10679946, Mumm. 2002. PubMed ID: 11855933, Table S2, Del Angel. 2020. PubMed ID: 32160374). In vitro functional studies demonstrate that this variant led to reduced enzyme activity compared to wildtype (Taillandier et al. 2000. PubMed ID: 10679946). This variant has not been reported in a large population database, indicating this variant is rare. Tis variant is interpreted as likely pathogenic. -

Infantile hypophosphatasia Uncertain:1

Uncertain significance, criteria provided, single submitter

clinical testing

Counsyl

Jan 02, 2018

- -

Computational scores

Source: dbNSFP v4.3

Name	Calibrated prediction	Score	Prediction
AlphaMissense	Pathogenic	0.89
BayesDel_addAF	Pathogenic	0.54	D
BayesDel_noAF	Pathogenic	0.54
CADD	Pathogenic	32
DANN	Uncertain	1.0
DEOGEN2	Pathogenic	0.95	D;.;.;D
Eigen	Pathogenic	0.75
Eigen_PC	Uncertain	0.65
FATHMM_MKL	Pathogenic	0.99	D
LIST_S2	Uncertain	0.95	.;D;D;D
M_CAP	Pathogenic	0.40	D
MetaRNN	Pathogenic	0.99	D;D;D;D
MetaSVM	Pathogenic	1.1	D
MutationAssessor	Uncertain	2.7	M;.;.;M
MutationTaster	Benign	1.0	D;D;D;D;D;D;D
PrimateAI	Uncertain	0.77	T
PROVEAN	Uncertain	-3.5	D;D;D;D
REVEL	Pathogenic	0.85
Sift	Uncertain	0.0010	D;D;D;D
Sift4G	Pathogenic	0.0010	D;D;D;D
Polyphen		1.0	D;.;.;D
Vest4		0.97
MutPred		0.93		Gain of methylation at K346 (P = 0.1912);.;.;Gain of methylation at K346 (P = 0.1912);
MVP		0.99
MPC		1.2
ClinPred		0.99	D
GERP RS		4.9
Varity_R		0.81
gMVP		0.86

Splicing

Name	Calibrated prediction	Score	Prediction
SpliceAI score (max)		0.010		Details are displayed if max score is > 0.2

Find out detailed SpliceAI scores and Pangolin per-transcript scores at spliceailookup.broadinstitute.org

Publications

LitVar

Other links and lift over

dbSNP: rs1553414563; hg19: chr1-21902270;