Introduction
We report a non-consanguineous couple, both carriers of pathogenic variants for hypophosphatasia, with 5 pregnancy losses.

Case Presentation
A 30-year-old woman and a 33-year-old man, with 5 pregnancy losses. The man has a history of childhood radius, ulna fractures, and normal height.

The first pregnancy loss occurred at 16.2 weeks. At first trimester ultrasound reported a short femur length and a crown-rump length of 73.5 mm with a decreased skull ossification. Skeletal dysplasia was suspected, but she had a miscarriage. The second and third pregnancies were lost 7 weeks, none of these losses were studied.

A diagnosis approach for recurrent pregnancy loss was initiated, and GTG-banding karyotype was performed on peripheral blood from both parents to rule out any balanced chromosomal rearrangement. The karyotypes were both reported as normal. She was homozygous for the MTHFR:c.1298G>A variant and, also had a uterine fibroid, which was removed.

The fourth and fifth pregnancies were lost at the 5th week, despite treatment with low-dose aspirin, enoxaparin, and progesterone, and the products of abortion were not studied either. She was examined by chromosomal microarray analysis and showed a single copy number increase of 476.56 kb in 16p12.2 (arr[GRCh37] 16p12.2(21964664_22441223)x3). This duplication was classified as a variant of uncertain significance and has not been reported in association with pregnancy loss or fetal death.

Diagnostic Workup
Due to the history of the first pregnancy with suspected skeletal dysplasia, a carrier screening was conducted to study some lethal autosomal recessive skeletal dysplasia that could recur in multiple pregnancies. A total of 302 genes were analyzed, and it was identified that she was a carrier of a pathogenic variant in ALPL:c.931G>A (NM_000478.5), and he was a carrier of a likely pathogenic variant in ALPL:c.1010A>G (NM_000478.5). These results are compatible with carrier status for hypophosphatasia, and a recurrence risk of 25% was established. Additionally, serum alkaline phosphatase was decreased in both individuals, while serum calcium and phosphorus levels were normal.

 

Treatment and Management
Three months later, two cycles of ovarian stimulation and follicular aspiration were performed, and after in vitro fertilization, six embryos were obtained. A trophectoderm biopsy was taken from each embryo for preimplantation genetic testing for monogenic diseases and aneuploidies (PGT-M/A).

 

Outcome and Follow-Up
Five of the six embryos were carriers, and one was affected; only two of the carrier embryos showed no chromosomal abnormalities, and those were the only ones that could be transferred.

Discussion
We believe that this result of carriers for hypophosphatasia could suggest that the first pregnancy was affected, though molecular confirmation was not possible. The other products were not studied either, as the losses occurred in the first trimester without prenatal findings consistent with hypophosphatasia. Therefore, we cannot be certain that they were affected or that this was the cause of the miscarriage. Both identified variants have been previously reported, ALPL:c.931G>A variant was found in a perinatal case involving a baby who died at birth with severe skeletal dysplasia, diagnosed via X-rays;  ALPL:c.1010A>G variant was associated with severe childhood hypophosphatasia. These variants have not been described as compound heterozygotes together.

 

Conclusion
In this case, it was of special interest to have a clue of fetal skeletal dysplasia in the first pregnancy; there are reports in which it has been shown that decreased levels of alkaline phosphatase prevent adequate implantation due to defective placentation. Which may explain the other losses. Having a confirmatory molecular test for hypophosphatasia made it possible to provide adequate genetic counseling and offer a reproductive option for the family.