ALAD

Chr 9AR

aminolevulinate dehydratase

Also known as: ALADH, PBGS

NCBI Gene: 210 ENSG00000148218 UniProt: P13716

The ALAD enzyme is composed of 8 identical subunits and catalyzes the condensation of 2 molecules of delta-aminolevulinate to form porphobilinogen (a precursor of heme, cytochromes and other hemoproteins). ALAD catalyzes the second step in the porphyrin and heme biosynthetic pathway; zinc is essential for enzymatic activity. ALAD enzymatic activity is inhibited by lead and a defect in the ALAD structural gene can cause increased sensitivity to lead poisoning and acute hepatic porphyria. Alternative splicing of this gene results in multiple transcript variants encoding different isoforms. [provided by RefSeq, Dec 2015]

Primary Disease Associations & Inheritance

{Lead poisoning, susceptibility to}MIM #612740

Porphyria, acute hepaticMIM #612740

UniProtAcute hepatic porphyria

Active trials

Pathogenic / LP

ClinVar variants

Pubs (1 yr)

1.2

Missense Z

0.87

LOEUF

Clinical Summary— ALAD

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Gene-Disease Validity (ClinGen)

porphyria due to ALA dehydratase deficiency · ARModerate

Moderate evidence — consider for supplementary testing

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Population Constraint (gnomAD)

Low constraint (pLI 0.00) — loss-of-function variants are relatively tolerated in the population.

Population Genetics & Constraint

gnomAD v4 — loss-of-function & missense intolerance

gnomAD

Tolerant — LoF & missense variants common in population

LoF Constraint?LOEUF (Loss-of-function Observed/Expected Upper bound Fraction) is the upper bound of the 90% CI for LoF OE — the preferred gnomAD v4 metric. Lower = more intolerant to LoF. LOEUF < 0.35 = highly constrained.

0.87LOEUF

pLI 0.000

Z-score 2.00

OE 0.51 (0.32–0.87)

Tolerant

Typical tolerance to LoF variation

Missense Constraint?Missense Z-score: standard deviations fewer missense variants observed vs. expected. Z > 3.09 (p < 0.001) = gene does not tolerate missense variation. OE missense < 0.6 is also considered constrained.

1.23Z-score

OE missense 0.76 (0.67–0.87)

157 obs / 206.8 exp

Tolerant

Mild missense constraint

Observed / Expected Ratios?Shaded band = 90% confidence interval. Vertical tick = point estimate. Grey threshold line = gnomAD constraint cutoff for that variant class.

LoF OE?Ratio of observed to expected LoF variants. Upper CI bound (LOEUF) ≤ 0.35 = strong LoF constraint signal.0.51 (0.32–0.87)

0≤0.351.4

Missense OE?Ratio of observed to expected missense variants. OE ≤ 0.6 = fewer missense variants than expected by chance.0.76 (0.67–0.87)

0≤0.61.4

Synonymous OE?Control metric — synonymous variants are largely neutral and expected near OE = 1.0. Significant deviation may indicate annotation issues.0.98

0≤1.21.6

LoF obs/exp: 10 / 19.5Missense obs/exp: 157 / 206.8Syn Z: 0.14

0.76top 25%

GOF

0.4677th %ile

LOF

0.2582th %ile

The highest-scoring mechanism for this gene is dominant-negative.

DNprediction above median

Note: In-silico variant effect predictors (SIFT, PolyPhen, REVEL, CADD) may underestimate pathogenicity of missense variants in genes with GOF or DN mechanisms. Consider functional evidence and clinical context.

Predictions from Badonyi M, Marsh JA. PLoS ONE. 2024;19(8):e0307312.