Lethal perinatal hypophosphatasia caused by a novel compound heterozygous mutation: a case report

A male infant was referred to our hospital due to tachypnea for 2 h after birth. He was a full-term infant of a G2P1 mother who had hypothyroidism and took euthyrox orally during pregnancy. His weight was 3560 g. Apger scores were 10 points and patient had no asphyxia after birth. Amniotic fluid was clear. Fetal heart monitoring suggested early deceleration, but there were no abnormality in umbilical cord and placenta. Prenatal B-scan ultrasonography at 25 weeks suggested that one side of the 2–4 vertebrae in fetal thoracic spine was small. However, complete fetal magnetic resonance imaging (MRI) showed no abnormality. Prenatal B-scan ultrasonography at 32 weeks suggested that the femurs were shorter than those at approximately 3 weeks gestation. The echoes on both sides of the thoracic spine were asymmetrical, and the corresponding parts of the spinal canal were thin. However, no more attention was paid to abnormal phenomena.

The infant gradually developed dyspnea 10 min after birth which was characterized by shortness of breath and cyanosis and accompanied by suction and sputum, and was then transferred to neonatal treatment. Physical examination results were as follows: his breath rate was 60 times / min, heart rate was 130 beats / min, length was 47 cm, head circumference was 34 cm, chest circumference was 31 cm. The symptoms of the patient were sobriety, poor response, convulsions, positive signs of three concaves, cyanosis of the lips. He had a short limbs, soft skull, narrow chest and soft abdomen. His bilateral lung breath sounds was rough without moist rale, heart sounds was strong and firm without pathologic murmur. His bowel sounds were normal, muscle force of the limbs was low, and the original reflection was incomplete. Blood test findings were as follows: PH 7.261, PO₂ 38mmhg, PCO₂ 55mmhg, Base excess 5 mmol/L, HCO₃ 22.6 mmol/L, Haemachrome 18.4 g/dl, suggesting type II respiratory failure.

Non-invasive ventilator was given immediately after admission, the dyspnea was relieved, and blood gas returned to normal. However, the children suffered from recurrent dyspnea after withdrawal, which was aggravated after activities or crying. Oxygen delivery could not be stopped and needs to be used repeatedly because of the dynamic increase of partial pressure of CO₂ in patients. On the 6th day after admission, epilepsies occurred, characterized by involuntary sucking movements, or systemic ankylosis, and the effect of anti-convulsant drugs was poor. Repeated dyspnea was a breakthrough point, the patient underwent chest X-ray, skull CT, long bone X-ray and laboratory examination. The chest and abdomen X-ray demonstrated thickened lung texture, visible ground-glass shadow, bell–shaped thoracic cage, thin ribs, and the absence of multiple attachments of the thoracolumbar spine (Fig. 1a). The X-ray of limb long bone demonstrated the bone characteristics on bilateral humerus, ulnar and radial bones, tibiofibula proximal and distal was irregular with multiple low-density lines. Bone fragments were seen on the distal femur (Fig. 1b). Head computed tomography (CT) demonstrated significantly reduced bone density and multiple skull osteogenesis imperfecta (Fig. 1c). Ophthalmologic consultation showed sclera was light blue. Serum biochemical test revealed that ALP was less than 5 IU/L in both measurements (normal range 45-125 IU/L). The level of blood calcium and phosphorus were normal. Based on the clinical and biochemical findings, the male infant was diagnosed as having HPP. Tracing the family history, his parents were asymptomatic, married and nonconsanguineous. To identify the underlying genetic defect, we performed molecular genetic testing for the ALPL gene. Parents were informed of the purpose of the study and signed the informed consent. The Ethics Committee of The First Hospital of Tsinghua University approved this study.

Genomic DNA was isolated from peripheral blood leukocytes using the DNA purifcation kit (Omega Bio-tek, Inc., Norcross, USA) according to the manufacturer’s instructions. All coding exons and their flanking intronic sequences of the ALPL gene were amplified by polymerase chain reaction (PCR) using primers (Shanghai biological engineering co. LTD, Shanghai, China) on a thermal cycler (Biosystems, Foster City, CA, USA). Direct sequencing was performed using the same primer sets and ABIBigDye3.1 kit (Biosystems, Rotkreuz, Switzerland) on the ABI313OXI genetic analyzer (Biosystems, Foster City, CA, USA). To identify any sequence variants, the sequences were compared with reference sequences for the ALPL gene (GRCh37/hg19) using chromas sequencher software (Technelysium, Australia). Two heterozygous missense variants were found in both alleles of this patient; they were separately from his parents. The father’s mutation was c.406C > T (p.R136C) and mother’s mutation was c.461C > T (p.A154V). The father and mother of the infant were confirmed to be heterozygous carriers of each variant (Fig. 2). Genetic testing confirmed the diagnosis of HPP.